Progress 07/01/98 to 06/30/05
Outputs
We identified the metabolic intermediates in phytoalexin synthesis. We used MALDI mass spectrometry as a tool to identify phytoalexins at pmol levels. We expanded this to include identification of other complex flavonoids. We plan to continue this work with the goal of identifying the actual intermediates in the biosynthetic pathway. We have been able to get C14 phenylalanine incorporated into the phytoalexin pathway. In the area of the fungal infection process and the fungal extracellular matrix, Dr. Inge Weiergang and I demonstrated the constitutive presence of an ECM from Cochliobolus carbonum.
Impacts
With Dr. Kirsten Nielsen in Denmark, a movie was produced that shows the accumulation of phytoalexins in sorghum by time- lapse photography and new work showed confocal images of the phytoalexins. This has allowed us to hypothesize that the site of accumulation is the endoplasmic reticulum.
Publications
- Osswald, W.; Stangarlin, J.R.; Nicholson, R.L.; Brummer, M.; Wulff, N.A.; Di Piero, R.M.; Piccinin, E.; Di Ciero, L.; Hoto, F.V.; Pascholati, S.F. 2004. The effect of acibenzolar-S-methyl on phytoalexin and PR-production induction on sorghum mesocotyls and on Colletotrichum sublineolum. Summa Phytopathologica 30 (4): 415-420.
- Nielsen KA, Gotfredsen CH, Buch-Pedersen MJ. AmmitzbOll H, Mattsson O, Duus JO, Nicholson RL. 2004. Inclusions of flavonoid 3-deoxyanthocyanidins in Sorghum bicolor self-organize into spherical structures. Physiological and Molecular Plant Pathology. 65:187-196.
- Weiergang I, Wood KV, Dunkle LD, Nicholson RL. 2004. In vivo growth and pathotoxin production by the maize pathogen Cochliobolus carbonum. Physiological and Molecular Plant Pathology. 64:273-279.
- Boddu J, Svabek C, Sekhon R, Gevens A, Nicholson RL, Jones AD, Pedersen JF, Gustine DL, Chopra S. 2004. Expression of a putative flavonoid 3 hydroxylase in sorghum mesocotyls synthesizing 3-deoxyanthocyanidins. Physiological and Molecular Plant Pathology. 65:101-113
- Christine K.Y. Yu, Karin Springob, Jurgen Schmidt, Ralph L. Nicholson, Ivan K. Chu, Wing Kin Yip, and Clive Lo. 2005, A Stilbene Synthase Gene (SbSTS1) Is Involved in Host and Non-host Defense Responses in Sorghum. Plant Physiology 138:393-401.
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Progress 10/01/03 to 09/30/04
Outputs
Sorghum synthesizes specific compounds, phytoalexins, in response to fungal infection. Phytoalexins are low-molecular-weight antimicrobial compounds that accumulate by de novo synthesis in response to infection. The synthesis of anthocyanidins has been well characterized, and genes that encode for their synthesis have been closed. In contrast, little is known of the route of biosynthesis of the deoxyanthocyanidin phytoalexins. Our work deals with physiological and molecular aspects of phytoalexin systhesis in sorghum. We have identified 5 compounds: luteolinidin, apigeninidin, a caffeic acid ester of arabinosyl-5-O-apigeninidin, 5-methoxy luteolinidin, and 7-methoxy apigeninidin. They are all fungitoxic. Toxicity assays demonstrated that the compounds prevent germination by, and kill conidia of Colletotrichum sublineolum, the sorghum anthracnose pathogen, at concentrations of 3uM. Time course profiles were made to determine whether the germination of conidia and
formation of appressoria require special conditions. Upon germination, each fungus produced a sheath of material that surrounded the emerging germ tube. The sheath was easily visualized by light microscopy using Differential Interference Contract (Nomarski) optics. The sheath around Cochliobolus carbonum was at first one layer and eventually became three layers in thickness. To induce appressorium formation the glass surface had to be treated to render it hydrophobic. Spores were induced to germinate witha 10-fold diultion of Fries' medium. Visualization of sheathes was enhanced by application of India ink to the conidia during the emergence of the germ tube and appresorium formation.
Impacts
Work with fungal adhesion affects both plant and animal health. Synthesis of flavonoids and other phenols (especially the deoxyanthocyanidins) is not completely understood
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Research is on the synthesis of phytoalexins by sorghum and characterization of mechanisms that account for resistance in maize and sorghum. Another project is determination of mechanisms of fungal adhesion and composition of the fungal extracellular matrix. The aim is to determine the basis of biochemical resistance in the Poaceae. In maize, genes for phenylpropanoid synthesis and distribution are turned on. In the past we identified the steps in resistance expression and showed they are linked to phenylpropanoid phenolic synthesis. The final expression of resistance is synthesis of cyanidin 3-dimalonyl glucoside, a zwitterion. It removes toxic charged compounds that accumulate in response to infection. In sorghum, phytoalexin synthesis requires genes similar to those essential for normal anthocyanidin synthesis. Both maize and sorghum are investigated for comparison of similarities and differences between pathways for anthocyanidin and deoxyanthocyanidin synthesis.
Results indicate that deoxyanthocyanidin synthesis is under the control of separate regulatory genes from those involved in normal pigment synthesis. Phytoalexin synthesis occurs independent of light. In sorghum, normal anthocyanidin and anthocyanin synthesis is turned off in response to infection and deoxyanthocyanidin synthesis is turned on. In sorghum, we cloned a cDNA of a pathogenesis related protein (PR-10) and demonstrated differential expression of defense-related genes following inoculation with Cochliobolus heterostrophus or Colletotrichum sublineolum. Characterization of the adhesive from Colletotrichum graminicola showed it is a high molecular weight glycoprotein. The extracellular matrix of Cochliobolus heterostrophus was characterized by light microscopy and its production characterized relative to stages in fungal morphogenesis from the onset of germination. The matrix was isolated, chemically characterized, and found to be a glycoprotein complex. The extracellular
matrix of Pestalotia malicola was shown to contain cutinase. In cooperation with colleagues in Wales and Japan we investigated the release of extracellular matrix by Blumeria graminis (the barley powdery mildew pathogen) conidia and Pestalotia and Helminthosporium species. We showed that recognition of the substratum occurs within seconds of contact. This work demonstrated initial events in signal transduction with these fungi. Matrix assisted laser desorption mass spectrometry was used to analyze complex phenols in plant disease extracts as well as flavonoid pigments, all in unpurified mixtures. This work was in collaboration with the Purdue Mass Spectrometry Center.
Impacts
Work with fungal adhesion affects both plant and animal health. Synthesis of flavonoids and other phenols (especially the deoxyanthocyanidins) is not completely understood
Publications
- Aguero, M.E, Gevens, A., and Nicholson, R.L. 2002. Interaction of Cochliobolus heterostrophus with phytoalexin inclusions in Sorghum bicolor. Physiological and Molecular Plant Pathology. 61:267-271
- Lo, C., Coolbaugh, R., Nicholson, RL. 2002. Molecular characterization and in silico expression analysis of a chalcone synthase gene family in Sorghum bicolor. Physiological and Molecular Plant Pathology. 61:179-188. Wright, A.J., Thomas, B.J., Kunoh, H., Nicholson, R. L., and Carver, T.L.W. 2002. Influences of substrata and interface geometry on the release of extracellular material by Blumeria graminis conidia. Physiological and Molecular Plant Pathology. 61:163-178.
- Chopra S, Gevens A, Svabek C, Wood KV, and Nicholson RL. 2002. Excision of the Candyststripe 1 transposon from a hyper-mutable Y1-cs allele shows that the sorghum Y1 gene controls the biosyntbesis of both 3-deoxyanthocyanidin phytoalexins and phobaphene pigments. Physiological and Molecular Plant Pathology. 60:321-330
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Progress 10/01/01 to 09/30/02
Outputs
Research concerns synthesis of phytoalexins by sorghum, characterization of resistance mechanisms in maize and sorghum, determination of mechanisms of fungal adhesion, composition of the fungal extracellular matrix, and events in signal transduction in the fungal/pathogen infection process. The aim is to determine the basis of biochemical resistance expression in the Poaceae. In maize, genes for phenylpropanoid synthesis and distribution are turned on. We have identified the steps in resistance expression and shown they are linked to phenylpropanoid phenolic synthesis. The final expression of resistance is synthesis of the zwitterion cyanidin 3-dimalonyl glucoside. It acts as a sink to remove toxic charged compounds that accumulate in response to infection. In sorghum, phytoalexin synthesis requires genes similar to those essential for normal anthocyanidin synthesis. Both maize and sorghum are investigated for comparison of similarities and differences between
pathways for anthocyanidin and deoxyanthocyanidin synthesis. Results indicate that deoxyanthocyanidin synthesis is under the control of separate regulatory genes from those involved in normal anthocyanidin synthesis. Sorghum phytoalexin synthesis occurs independent of light. Sorghum turns off normal anthocyanidin and anthocyanin synthesis in response to infection and turns on deoxyanthocyanidin synthesis. In sorghum, we cloned a cDNA of a pathogenesis related protein (PR-10) and demonstrated differential expression of defense-related genes following inoculation with Cochliobolus heterostrophus or Colletotrichum sublineolum. Characterization of the adhesive from Colletotrichum graminicola showed it to be a high molecular weight glycoprotein. The extracellular matrix of Cochliobolus heterostrophus was visually characterized by light microscopy and its production characterized relative to stages in fungal morphogenesis from the onset of germination. The matrix was isolated, chemically
characterized, and found to be a complex of glycoproteins. The extracellular matrix of Pestalotia malicola was shown to contain cutinase. In international cooperative work, we investigated the release of extracellular matrix by Blumeria graminis (the barley powdery mildew pathogen) conidia and showed that recognition of the substratum occurs within seconds of contact. This work demonstrated initial events in signal transduction with this obligate pathogen. Matrix assisted laser desorption mass spectrometry was used to analyze complex phenols in plant disease extracts as well as flavonoid pigments, all in unpurified mixtures. This work was in collaboration with the Purdue Mass Spectrometry Center.
Impacts
Work with fungal adhesion affects both plant and animal health. Synthesis of flavonoids of the deoxyanthocyanidin class is not completely understood
Publications
- Chopra S, Gevens A, Svabek C, Wood KV, and Nicholson RL. 2002. Excision of the Candyststripe 1 transposon from a hyper-mutable Y1-cs allele shows that the sorghum Y1 gene controls the biosyntbesis of both 3-deoxyanthocyanidin phytoalexins and phobaphene pigments. Physiological and Molecular Plant Pathology. 60:321-330
- Nicholson, RL, Wood KV. 2001. Phytoalexins and secondary products, Where are they and how can we measure them? Physiological and Molecular Plant Pathology. 59:63-69
- Nicholson, RL. 2001. Phenylalnine ammonia-lyase. 2001 In. Encyclopedia of PLANT Pathology. Maloy and and Murry. Wiley and Sons. 757-759.
- Nicholson, RL. 2001. Phytoalexins. In. Encyclopedia of Plant Patholoogy. Maloy and Murry. Wiley and Sons. 761-762.
- Gevens, AJ, Carver TLW, Thomas BJ, Nicholson RL. 2001. Visualization and partial characterization of the ECM of Pestalotia malicola on artificial and natural substrata. Physiological and Molecular Plant Pathology 58:277-285
- Hammerschmidt, R and Nicholson, RL. 2001. A Survey of Plant Defense Responses to Pathogens. In Inducible plant defenses against pathogens and herbivores: Biochemistry, ecology, and agriculture. pp 57-71. American Phytopathological Society.
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Progress 10/01/00 to 09/30/01
Outputs
Research involves identifying the compounds made by sorghum and corn that protect these plants from disease. These plants are important grains and are essential to our economy as well as food needs. In sorghum, resistance compounds are deoxyanthocyanidins . They function as phytoalexins. Because they are colored, they are 'easy' to work with. They provide a significant tool for learning about how the plant protects itself from fungal pathogens. In corn, the compounds are phenylpropanoid phenols. All of these compounds are toxic to fungi. Other work involves learning how fungi stick to plants. This is important because if a fungus does not stick disease can not occur. Colletotrichum graminicola spores stick to leaves within minutes of contact. The same thing happens with the sorghum anthracnose fungus, Colletotrichum sublineolum. Importantly, spores only stick if the leaf surface is very hydrophobic. Another pathogen that we work with is the fungus, Blumeria graminis
which causes powdery mildew of barley. With each of these fungi we are trying to understand how the extracellular matrix materials are released. Work in collaboration with researchers in Wales, Japan and Denmark has led us to the discovery that some of the components of the matrix function as 'messengers' in signal transduction. It is sort of how the fungi and their plant hosts 'talk' to each other. We seek to determine if plants with less hydrophobic leaves can serve as tools for resistance. We have started to learn what the adhesive molecules are and when they are produced by various fungal pathogens. It's a sticky business that should lead to increased crop production!
Impacts
Once we are able to identify the ways plants protect themselves, we can then use that information to assist the plants to do a better job. This should allow us to decrease the use of environmentally harmful pesticides. The increase in productivity will improve the health and social well being of all of our citizens.
Publications
- Nicholson, R.L., 2001. Phytoalexins: in Encyclopedia of Plant Pathology. Vol 2. ed. Maloy and Murray, John Wiley & Son, Inc.
- Meguro, A., Fujita, K, Kunoh, H., Carver, TLW, and Nicholson, RL. 2001. Release or the extracellular matrix from conidia of Blumeria graminis in relation to germination. Mycoscience 42:201-209.
- Nicholson R.L., 2001. Phenylalanine ammonia lyase: in Encyclopedia of Plant Pathology. Vol. 2. ed. Maloy and Murray, John Wiley & Son. Inc.
- Gevens, A., Carver T.L.W., Thomas, B.J., and Nicholson, R.L. 2001. Visualization and partial characterization of the extracellular matrix of Pestalotia malicola. Physiological and Molecular Plant Pathology. 58: 277-285.
- Gevens, A. and Nicholson, R.L. 2000. Cutin composition: A subtle role for fungal cutinase? Physiological and Molecular Plant Pathology. 57:43-45
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Progress 10/01/99 to 09/30/00
Outputs
> The purpose of this research was to provide cow-calf producers data on the potential merits of using a rotational stocking system with eight paddocks as compared to two paddocks. This research was conducted in 2000 at two sites at the Feldun-Purdue Agricultural Center, Bedford, IN. Stocking rate was similar between the 2-paddock and 8-paddock systems. With the stocking rate utilized, one cow-calf pair per 0.61 hectare, and an exceptional forage production year, dry matter intake was not limited on either system. At weaning, 11 and 12 October, average calf weights were 299 and 289 kg for the 2- and 8-paddock systems, respectively. The 8-paddock system was credited with producing 1 Mg per hectare of hay during the grazing season and 40 more grazing days in the autumn. No hay was harvested on the 2-paddock system. Value of the hay produced and extra grazing days in the autumn with the 8-paddock system is, conservatively, a credit of $45 to each cow. A debit of $20 per
cow in the 8-paddock system occurred, as weaning weight was 10 kg lower as compared to the 2-paddock system. Therefore, $25 more return per cow resulted with the 8-paddock system.
Impacts
A rotational stocking system utilizing eight paddocks instead of 2 paddocks resulted in $25 more return per cow. Expectations of the 8-paddock system, as compared to a 2-paddock system, are hay production from a couple of paddocks and more grazing days in the autumn. Value of the hay produced and extra grazing days in the autumn with the 8-paddock system was at least $45 per cow. A debit of $20 per cow in the 8-paddock system occurred, as weaning weight was slightly lower as compared to the 2-paddock system.
Publications
- Carter, Ben, and Johnson, Keith D. 2000. Performance of alfalfa in Indiana, 1996-1999. Purdue Univ. Bulletin B-792. 21 p.
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Progress 10/01/98 to 09/30/99
Outputs
Research concerns the synthesis of fungitoxic phytoalexins by sorghum, characterization of resistance mechanisms in maize, and determination of mechanisms of fungal adhesion, composition of the fungal extracellular matrix, and events in signal transduction in fungal pathogens during the infection process. The program aims to determine the basis of biochemical resistance expression in the Poaceae. In maize, genes for phenylpropanoid synthesis and distribution are turned on. We identified each of the steps in resistance expression and showed they are specifically linked to phenylpropanopoid phenol synthesis. The final expression of resistance is synthesis of the zwitterionic compound cyanidin 3-dimalonyl glucoside. We proposed that it acts as a sink to remove toxic charged compounds that accumulate in response to infection. In sorghum, phytoalexin synthesis requires genes similar to those essential for normal anthocyanidin synthesis. Both maize and sorghum are
investigated for comparison of similarities and differences between pathways for anthocyanidin and deoxyanthocyanidin synthesis. Results indicate that deoxyanthocyanidin synthesis is under the control of separate regulatory genes from those involved in normal anthocyanidin synthesis. Sorghum phytoalexin synthesis occurs independent of light. In response to infection, sorghum turns off normal anthocyanidin and anthocyanin synthesis and turns on deoxyanthocyanidin synthesis. In sorghum, we cloned a cDNA of a pathogenesis related protein (PR-10) and demonstrated differential expression of defense-related genes following inoculation with Cochliobolus heterostrophus or Colletotrichum sublineolum. Characterization of the adhesive from Colletotrichum graminicola showed it to be a high molecular weight glycoprotein. The extracellular matrix of Cochliobolus heterostrophus was visually characterized by light microscopy and its production characterized temporally relative to changing stages in
fungal morphogenesis from the onset of germination. The matrix was isolated, chemically characterized, and found to be a complex of glycoproteins. The extracellular matrix of Pestalotia malicola was shown to contain cutinase and suggested to be the reason why the fungus grows exclusively on fruit cutin. In international cooperative work, we investigated the release of extracellular matrix by Blumeria graminis (the barley powdery mildew pathogen) conidia and showed that recognition of the substratum occurs withing seconds of contact. This is the first work to demonstrate initial events in signal transduction with this obligate pathogen. Matrix assisted laser desorption mass spectrometry was used to analyze complex phenols in plant disease extracts as well as a variety of flavonoid pigments, all in unpurified mixtures. This work was a collaboration with the Purdue Mass Spectrometry Center.
Impacts
The impact is that we will be able to identify the ways that these plants protect themselves. Then we can use that information to assist the plants to do a better job. This is important because it should allow us to decrease the use of environmentally harmful pesticides. In turn, the increase in food productivity will increase the health and social well being of all of our citizens.
Publications
- Sugui, JA., Wood, KV., Yang, Z., Bonham, CC., and Nicholson, RL. 1999. Matrix-assisted laser desorption ionization mass spectrometry analysis of grape anthocyanins. American J. Enology and Viticulture. 50: 199-203
- Sugui, J.A., Kunoh, H., and Nicholson, R.L. 1999. Detection of protein and carbohydrate in the extracellular matrix released by Cochliobolus heterostrophus during germination. Mycoscience. 40: 11-19
- Lo, Sze-Chung Clive, Hipskind, J. D., and Nicholson, R. L. 1999. cDNA cloning of a sorghum pathogenesis related protein (PR-10) and differential expression of defense-related genes following inoculation with Cochliobolus heterostrophus or Colletotrichum sublineolum. Molecular Plant-Microbe Interactions 12: 479-489.
- Carver, T.L.W., Kunoh, H. Thomas, B.J., and Nicholson, R.L. 1999. Release and Visualization of the Extracellular Matrix of Conidia of Blumeria graminis . Mycological Rearch. 103:547-560..
- Sugui, J.A., Leite, B., and Nicholson, R.L. 1998. Partial characterization of the extracellular matrix released onto hydrophobic surfaces by conidia and conidial germlings of Colletotrichum graminicola. Physiological and Molecular Plant Pathology. 52:411-425.
- Suzuki, Shunji; Komiya, Yukiko; Mitsui, Tomohiro; Tsuyumu Shinji;Kunoh, Hitoshi; Carver, Timothy L. W; and Nicholson, Ralph L. 1998. Release of cell wall degrading enzymes from conidia ofBlumeria graminis on artificial substrata. Annals of the Phytopathological Society of Japan. 64:160-167.
- Sze-Chung Clive Lo and Ralph L. Nicholson, 1998. Reduction of Light-Induced Anthocyanin Accumulation in Inoculated Sorghum Mesocotyls Implications for a Compensatory Role in the Defense Response. Plant Physiology 116:979-989.
- Sugui, J.A., Pascholati, S.F., Kunoh, H., Howard, R.J., and Nicholson, R.L. 1998. Association of Pestalotia malicola with the plant cuticle: Visualization of the pathogen and detection of cutinase and non-specific esterase. Physiological and Molecular Plant Pathology. 52:213-221.
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Progress 10/01/97 to 09/30/98
Outputs
Research concerns the synthesis of the fungitoxic phytoalexins in sorghum, characterization of resistance in maize to disease, and determination of mechanisms of fungal adhesion, composition of the fungal extracellular matrix, and events in signal transduction in fungal pathogens during the infection process. The program aims to determine biochemical steps in resistance expression in the Poaceae. In maize, genes for phenylpropanoid synthesis and distribution are turned on. We identified the final product of resistance expression as the zwitterionic pigment cyanidin 3-dimalonyl glucoside and propose that it acts as a sink to remove toxic charged compounds that accumulate in response to infection. In sorghum, steps in phytoalexin synthesis require genes similar to those essential for normal anthocyanidin synthesis. Both maize and sorghum are being investigated for comparison of similarities and differences between pathways for anthocyanidin and deoxyanthocyanidin
synthesis. Results indicate that deoxyanthocyanidin synthesis is under the control of separate regulatory genes from those involved in normal anthocyanidin synthesis. In sorghum phytoalexin synthesis occurs independent of light. In response to infection, sorghum turns off normal anthocyanidin and anthocyanin synthesis and turns on deoxyanthocyanidin synthesis. Characterization of the adhesive and from Colletotrichum graminicola showed it to be a high molecular weight glycoprotein. The extracellular matrix of Cochliobolus heterostrophus was visually characterized by light microscopy and its production characterized temporally relative to changing stages in fungal morphogenesis from the onset of germination. The matrix was then isolated and chemically characterized and found to be a complex of glycoproteins. The extracellular matrix of Pestalotia malicola was shown to contain cutinase and suggested to be the reason why the fungus is capable of growing exclusively on fruit cutin.
Impacts
(N/A)
Publications
- Sze-Chung Clive Lo and Ralph L. Nicholson, 1998. Reduction of Light-Induced Anthocyanin Accumulation in Inoculated Sorghum Mesocotyls Implications for a Compensatory Role in the Defense Response. Plant Physiology 116:979-989.
- Sugui, J.A., Pascholati, S.F., Kunoh, H., Howard, R.J., and Nicholson, R.L. 1998. Association of Pestalotia malicola with the plant cuticle: Visualization of the pathogen and detection of cutinase and non-specific esterase. Physiological and Molecular Plant Pathology. 52:213-221.
- Suzuki, Shunji; Komiya, Yukiko; Mitsui, Tomohiro; Tsuyumu Shinji;Kunoh, Hitoshi; Carver, Timothy L. W; and Nicholson, Ralph L. 1998. Release of cell wall degrading enzymes from conidia ofBlumeria graminis on artificial substrata. Annals of the Phytopathological Society of Japan. 64:160-167.
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Progress 10/01/96 to 09/30/97
Outputs
Research concerns the synthesis of the fungitoxic phytoalexins in sorghum, characterization of resistance in maize to disease, and determination of mechanisms of fungal adhesion and composition of the fungal extracellular matrix. The program aims to determine the biochemical steps in resistance expression in the Poaceae. In maize, genes for phenylpropanoid synthesis and distribution are turned on. We identified the final product of resistance expression as the zwitterionic pigment cyanidin 3-dimalonyl glucoside that we propose acts as a sink to remove toxic charged compounds that accumulate in response to infection. In sorghum, steps in phytoalexin synthesis require genes similar to those essential for normal anthocyanidin synthesis. Both maize and sorghum are being investigated for comparison of similarities and differences between pathways for anthocyanidin and deoxyanthocyanidin synthesis. Results indicate that deoxyanthocyanidin synthesis is under the control of
separate regulatory genes from those involved in normal anthocyanidin synthesis. In sorghum phytoalexin synthesis occurs independent of light. In response to infection, sorghum turns off anthocyanin synthesis and turns on deoxyanthocyanidin synthesis. Characterization of the adhesive(s) from Colletotrichum graminicola shows that they are high molecular weight glycoproteins. A laccase enzyme was identified in the extracellular conidial matrix of C. graminicola. The extracellular matrix of Pestalotia malicola was shown to contain cutinase.
Impacts
(N/A)
Publications
- Hipskind, J.D., Nicholson, R.L., and Goldsbrough, P.B. 1996. Isolation of a cDNA encoding a novel leucine-rich repeat motif from Sorghum bicolor inoculated with fungi. Molecular Plant Microbe Interactions 9:819-825.
- Weiergang, I., Hipskind, J.D., and Nicholson, R.L. 1996. Synthesis of 3-deoxyanthocyanidin phytoalexins in sorghum occurs independent of light. Physiological and Molecular Plant Pathology. 49: 377-388..
- Anderson, D.W., and Nicholson, R.L. 1996. Characterization of a laccase in the conidial mucilage of Colletotrichum graminicola. Mycologia. 88:996-1002.
- Hipskind, J., Wood, K., and Nicholson, R.L. 1996. Stimulation of anthocyanin accumulation and delineation of pathogen ingress in maize genetically resistant to Bipolaris maydis race O. Physiological and Molecular Plant Pathology. 49:247-256.
- Hipskind, J.D., Goldsbrough, P.B., Urmeev, F., and Nicholson, R.L. 1996. Synthesis of 3-deoxyanthocyanidin phytoalexins in sorghum does not occur via the same pathway as 3-hydroxylated anthocyanidins and phlobaphenes. Maydica 41;155-166.
- Nicholson RL, and Hipskind JD. 1996. Resistance in the Poaceae: Different Roles for Phenolic Compounds. in Proceedings of the Japan-US scientific seminar on Molecular Aspects of Pathogenicity and Host Resistance: Requirements for Signal Transduction. pp. 209-217. D Mills, H. Kunoh, NT Keen, and S. Mayama, eds., APS Press.
- Epstein L, and Nicholson RL. 1997. Adhesion of spores and hyphae to plant surfaces. THE MYCOTA: Carroll G, Tudzynski P (eds.). Vol V, Part A, p. 11-25.
- Lo, S-C C., and Nicholson, R.L. 1997. Reduction of Light-Induced Anthocyanin Accumulation in Inoculated Sorghum Mesocotyls: Implications for a Compensatory Role in the Defense Response. Plant Physiology (in press).
- Sugui, J.A., Pascholati, S.F., Kunoh, H., Howard, R.J., and Nicholson, R.L. 1998. Association of Pestalotia malicola with the plant cuticle: Visualization of the pathogen and detection of cutinase and non-specific esterase. Physiological and Molecular Plant Pathology (in press).
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Progress 10/01/95 to 09/30/96
Outputs
Research concerns the synthesis of the fungitoxic phytoalexins in sorghum, characterization of resistance in maize, and determination of mechanisms of fungal adhesion. The program aims to discover the biochemical steps in resistance expression. In maize, steps include the turning on of genes for phenylpropanoid synthesis and distribution. We identified the final product of resistance expression as the pigment cyanidin 3-dimalonyl glucoside. Evidence suggests that the compound acts as a sink to remove toxic phenols that accumulate in response to infection. In sorghum, steps in phytoalexin synthesis require the same or similar genes that are essential for normal anthocyanidin synthesis. Both maize and sorghum are being investigated for comparison of similarities and differences between pathways for anthocyanidin and deoxyanthocyanidin synthesis. Results indicate that deoxyanthocyanidin synthesis is under the control of separate regulatory genes from those involved in
normal anthocyanidin synthesis. A new sorghum phytoalexin, 5-methoxyluteolinidin was identified by Plasma desorption mass spectrometry. Work on fungal adhesion shows that conidia of Colletotrichum species adhere prior to germination and after germination. Ungerminated conidia only adhere to hydrophobic surfaces. Characterization of the adhesive(s) shows that it is glycoprotein. Conidia of Cochliobolus heterostrophus adhere only after germ tube emergence. Adhesion also results from the release of glycoproteins.
Impacts
(N/A)
Publications
- M. Nicole and V. Gianin Hipskind JD, et al. 1996. Synthesis of 3-deoxyanthocyanidin phytoalexins in sorghum does not occur via the same pathway as 3-hydroxylated anthocyanidins andphlobaphenes. Maydica (in press). Lo S-C, et al. 1996. Phytoalexin accumulation in sorghum: Identification of a methyl ether of luteolinidin. Physiol. Molec. Plant Pathol. 49:21-31.
- Weiergang I, et al. 1996. Morphogenic regulation of pathotoxin synthesis in Cochliobolus carbonum. Fungal Genetics and Biology 20:74-78.
- Orczyk W, et al. 1996. Stimulation of phenylalanine ammonia-lyase in sorghum in response to inoculation with Bipolaris maydis. Physiol. Molec. Plant Pathol. 48.
- Hipskind J, et al. 1996. Stimulation of anthocyanin accumulation and delineationof pathogen ingress in maize genetically resistant to Bipolaris maydis race O. Physiol. Molec. Plant Pathol. (in press).
- Anderson DW, Nicholson RL. 1996. Characterization of a laccase in the conidial mucilage of Colletotrichum graminicola. Mycologia (in press).
- Nicholson RL, Hipskind JD. 1996. Resistance in the Poaceae: Different Roles for Phenolic Compounds. in Proceedings of the Japan-US scientific seminar on Molecular Aspects of Pathogenicity and Host Resistance. APS Press.
- Nicholson, RL. 1996. Adhesion of Fungal Propagules: Significance to the success of the fungal infection process. pages 117-134, in Histology, Ultrastructure andMolecular Cytology of Plant-Microorganism Interactions.
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Progress 10/01/94 to 09/30/95
Outputs
Research concerns the synthesis of the fungitoxic deoxyan-thocyanidin phytoalexins in sorghum and characterization of resistance expression in maize. The program aims to discover each of the steps in the expression of resistance by these plants. In maize, steps include the turning on of genes for phenylpropanoid synthesis and their distribution in the tissue. We identified the final product of resistance expression as the pigment cyanidin 3-dimalonyl glucoside. Evidence suggests that the synthesis of the compound acts as a sink to remove toxic phenols. In sorghum, steps in phytoalexin synthesis seem to require the same or similar genes that are essential for normal anthocyanidin synthesis. Both maize and sorghum are being investigated for comparison of similarities and differences between pathways for anthocyanidin and deoxyanthocyanidin synthesis. Results indicate that deoxyanthocyanidin synthesis is under the control of separate regulatory genes from those involved
in normal anthocyanidin synthesis. Plasma desorption mass spectrometry has been developed as a tool for the rapid identification of phenolic secondary products involved in resistance expression. Other work involves adhesion of conidia of Colletotrichum graminicola. Conidia adhere to hydrophobic surfaces in minutes of contact. Adhesion results from the release by conidia of glycoproteins that bind the spore to the substratum.
Impacts
(N/A)
Publications
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Progress 10/01/93 to 09/30/94
Outputs
Research concerns the regulation of synthesis of the fungitoxic deoxyanthocyanidin phytoalexins in sorghum and the characterization of the expression of resistance in maize. The program aims to discover the final steps in the expression of resistance in maize. These steps appear to include the turning on of chalcone synthase as well as other genes required for flavonoid synthesis. The final product of resistance expression was identified as cyanidin 3-dimalonyl glucoside. In sorghum the steps in phytoalxin synthesis appear to require a unique enzyme for the reduction of a flavanon intermediate in the path to deoxyanthocyanidin synthesis. Both the maize and sorghum responses are being investigated for comparison of similarities and differences between the pathways. Other work involves adhesion of conidia of Colletotrichum graminicola. Conidia adhere to hydrophobic surfaces within minutes of contact. Adhesion results from the release of a glycoprotein from the conidium
that binds the conidium to the substratum. Work with Erysiphe graminis has revealed that the fungus stimulates the barley plant to produce a unique compound as a response to infection. The compound prevents the fungus from forming an haustorium. The molecular weight of the compound is 290 and it resembles a hordatine.
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Progress 10/01/92 to 09/30/93
Outputs
Research concerns the regulation of synthesis of the fugitoxic deoxyanthocyanidin sorghum phytoalexins. Synthesis requires phenylalanine ammonia-lyase and chalcone synthase. The program is aimed at discovering the final steps in phytoalexin synthesis. We found a way to identify deoxyanthocyanidins using mass spectrometry. We showed that compound synthesis is a characteristic that predicts the ability of sorghum cultivars to resist the anthracnose disease. The work gives a basis for understanding flavonoid regulation in plants. In corn we studied 4-hydroxycinnamic acid CoA ligase and evaluated it as a regulator of resistance expression. The enzyme exists as a single isoform in tissue responding to infection indicating that it is not involved in regulation of resistance. Rather, it is a secondary factor necessary for the continued production of phenylpropanoids during resistance expression. Other work involves adhesion and how fungi stick to their host plants. In
Colletotrichum graminicola we found that conidia begin to adhere immediately upon contact with a hydrophobic surface and that the adhesive is a glycoprotein. The work will lead us to understanding the initial factors that regulate the fungal infection process. Work with Erysiphe graminis has shown that this fungus initiates the infection process by altering the surface hydrophobicity of leaves of its barley host. The work answers questions about surface recognition required for the fungal infection process.
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Progress 10/01/91 to 09/30/92
Outputs
My research has involved the characterization of the accumulation of fungitoxic phytoalexins, the deoxyanthocyanidins, in sorghum at the cellular level. We found that these fungitoxic compounds accumulate within single plant cells to levels that are approximately 50,000 times greater than those required to kill fungal pathogens. This work is important since it is the first to demonstrate the specific site of accumulation of plant resistance compounds at the cellular level and since it proves that these compounds accumulate within the plant cells that are under attack. Other work has identified a self-inhibitory compound from the fungus Colletotrichum graminicola. The compound was identified as mycosporine-alanine. Because the compound prevents spore germination we hope to develop its use for the control of plant diseases. Work with several different fungal pathogens has centered on the ability of these organisms to degrade the plant cuticle by the production of
cutinase enzymes. Results have shown that many fungi produce cutinases and that the role of the enzyme is probably associated with adhesion of the fungus to the plant surface rather than with penetration of the plant cuticle. This is significant since it emphasizes the importance of adhesion to the success of pathogenicity and rejects the assumption that the enzyme is required for fungi to penetrate into their host plants.
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Progress 10/01/90 to 09/30/91
Outputs
Research on the importance of hydroxycinnamic acid CoA ligase in maize disease interactions has continued. Monoclonal antibodies have been prepared and we are presently attempting to find the gene(s) for CoA ligase. With the Sorghum/Colletotrichum interaction we are continuing to pursue the route of synthesis of the deoxyanthocyanidins in addition to attempting the purification of the elicitor from the fungus. In the studies of the conidial mucilage from Colletotrichum (the origin of the sorghum phytoalexin elicitor) we have now discovered a naturally produced self inhibitor. We have purified the inhibitor and its chemical identification is underway.
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Progress 10/01/89 to 09/30/90
Outputs
Research has continued on the importance of hydroxycinnamte CoA ligase and potential isozymes of this enzyme in the expression of resistance to fungal infection by maize. We have now isolated the enzyme in a nearly pure form (3 to 4 peptides) and have begun the process of attempting to make monoclonal antibodies for use in future studies. Work with the sorghum-Colletotrichum graminicola interaction has demonstrated that the fungus produces an elicitor of phytoalexin synthesis in sorghum. We have partially characterized the elicitor and found two components with activity. One is a small carbohydrate oligomer and the second is a small peptide (approximately 18 kD). The elicitor active peptide stimulates the synthesis of the deoxyanthocyanidin phytoalexins in sorghum mesocotyls. The compounds accumulate linerly over time and linearly with respect to the dosage of elicitor applied.
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Progress 10/01/88 to 09/30/89
Outputs
Research with resistance has shown that isozymes of hydroxycinnate CoA ligase isozymes are the probable key factors in the first expression of resistance. Work with sorghum resistance has resulted in the identification of a third phytoalexin, a caffeic acid ester of arabinosyl-5-0-apigeninidin. Chalcone synthase activity in the sorghum interaction was found to increase within 6 h of the time of inoculation and was followed 3 h later by the first detection of phytoalexin synthesis. The subcellular location of phytoalexin synthesis has been identified. It occurs in bodies (vesicles) within the cell that is under attack. The bodies coalesce, move to the site of appressorial attachment and deposit their contents into the host cell. The phytoalexins kill the host cell and leach into the attached fungus killing it as well.
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Progress 10/01/87 to 09/30/88
Outputs
In our corn research with the Pathogen Helminthosporium maydis we have demonstrated that the expression of resistance involves the redistribution of phenylpropanoid phenols as an immediate response to fungal infection. First there is an accumulation of two caffeoyl esters (one is a glucose ester, the other is an ester of an organic acid) that begins within 18 h of inoculation. The esters are not fungitoxic and are synthesized in both susceptible and resistant cultivars. Second there is an accumulation of ferulic and p-coumaric acids as products esterified to the host cell wall. This occurs faster and to a greater extent in the resistant cultivar. Third there is deposition of phenylpropanoids into a lignin component that surrounds the lesion. This lignin differs from normal lignin as it contains a high level of syringyl residues. Lignin deposition begins at around 48 h in the resistant host and 72 h in the susceptible host. At 8 h after inoculation there is an increase
in 4-hydroxycinnamic acid CoA ligase and isozymes with differential substrate specificity for the phenylpropanoids have been identified. The isozymes differ in resistant and susceptible cultivars. In sorghum we have shown the synthesis of two phytoalexins of the 3-deoxyanthocyanidin class, apigeninidin and luteolinidin. These occur in leaves and mesocotyls and are synthesized rapidly and in single cells.
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Progress 01/01/87 to 12/30/87
Outputs
Patterns of 4-hydroxycinnamic acid: CoA ligase isozymes in maize cultivars with differential resistance and susceptibility to Helminthosporium maydis race 0 have been identified in mesocotyls and leaves. Activity toward 5-hydroxyferulic acid has been discovered and may explain the means through which sinapyl residues appear in lignin synthesized by maize. Substrate specificity studies shows that changes in isozyme activities parallel changes in phenylpropanoid redirection in response to infection. In resistance ferulic and p-coumaric acids are first esterified to the cell wall and then lignin with a very high sinapyl alcohol content is formed. This constitutes the process of lesion restriction. Similar events occur in the susceptible interaction but at a very much slower rate. Papilla formation in corn epidermis was shown to be nonspecific, that papillae are composed in part of lignin, and that peroxidase isozyme patterns shift to include two additional isozymes at
the time of papilla formation. It is thought that these peroxidases are specific to papilla lignin formation. Phytoallexin synthesis in sorghum has been identified. The phytoalexins are the 3-desoxyanthocyanidins apiginidin and luteolinidin. A family of eight compounds was identified, each exhibiting fungitoxicity. This is only the third report of phytoalexins to be formed in monocots.
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Progress 01/01/86 to 12/30/86
Outputs
Patterns of 4-hydroxycinnamic acid: CoA ligase activities in maize cultivars with differential resistance and susceptibility to Helminthosporium maydis race 0 have been studied. Multiple peaks of CoA ligase activity have been detected in protein extracts separated by column chromatography. Elution profiles differentiated the uninoculated susceptible from the uninoculated resistant cultivars & inoculation changed the elution profiles for the respective cultivars and further differentiated the resistant from the susceptible hosts by their disease interactions indicating the involvement of isozymes in the response to infection. The specific role of the isozymes in the disease interactions is under investigation with the first step being isozyme purification and substrate specificity studies. Work with the anthracnose pathogen, Colletrotrichum graminicola, has shown that the spore mucilage contains specific proline rich glycoproteins with exceptionally high affinity
for binding polyphenols, including those phenylpropanoids which accumulate in the lesion margin at the time of restriction. We have proposed that these glycoproteins function as virulence factors and aid in the spread and development of disease by acting as a fungal defense mechanism against potentially toxic plant phenols.
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Progress 01/01/85 to 12/30/85
Outputs
We continue to use the etiolated maize mesocotyl as a research tool for disease physiology. We have now found that the fungus Helminthosporium maydis induces susceptibility in the corn plant and our evidence shows that this occurs by preventing the expression of phenolic synthesis. This seems to be at the level of phenylalanine ammonia lyase (PAL). We have also found that PAL is not activated above basal levels in response to resistant host-pathogen combinations but is activated above basal levels in response to wounding. Work with the anthracnose disease has shown that the stress of senescence allows for increased susceptibility and senescence itself is induced by the fungus.
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Progress 01/01/84 to 12/30/84
Outputs
We have investigated the flow of phenylpropanoids in etiolated maze mesocotyls inoculated with Helminthosporium maydis or Helminthosporium carbonum. The mesocotyls did not accumulate free or free esterified phenylpropanoids as a result of infection. Base hydorlyzable wall bound phenylpropanoids (primarily ferulic acid) did accumulate but only in the resistant interaction of rhm maize with H. maydis. Resistant plants inoculated with H. maydis also exhibited a shift toward synthesis of pelargonidin and away from cyanidin as the principal aglycone of anthocyanins. There were no new anthocyanin compounds synthesized but there was a shift toward different amounts of specific compounds.
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Progress 01/01/83 to 12/30/83
Outputs
Using etiolated maize mesocotyls we have found that Helminthosporium maydis induces hydroxycinnamate: CoA ligase in both resistant (rhm) and susceptible maize. The increase begins at the time of penetration, between 6 and 9 hr after inoculation. In the resistant interaction the increase is linear over a 48 hr period whereas in the susceptible response activity levels off at 12 hr after inoculation. Levels of activity in uninoculated tissue are typically 2 to 5 nmol p-coumaroyl CoA minEPGgEPGfw and 10 to 25 nmol minEPGgEPGfw in resistance. It was found that when H maydis was inoculated onto plants after H. carbonum that H. maydis blocked the expression of resistance to H. carbonum. The block was not just of symptoms since fungal growth (measured microscopically) increased significantly after the challenge inoculation. Hyphal growth in challenged tissue reached a mean of 75 m by 60 h post challenge as compared to 10 m in unchallenged tissues. The results strongly
suggest that induced susceptibiity occurs in maize in response to H. maydis.
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Progress 01/01/82 to 12/30/82
Outputs
Biosynthesis of the phenolic phenylpropanoids has been investigated using etiolated corn mesocotyls. Enzymes of phenol synthesis which were studied include phenylalanine ammonia lyase (PAL) and 4-coumarate: CoA ligase. When inoculated in either susceptible (Helminthosporium maydis) or resistant (H. carbonum) host-parasite combinations no changes in PAL were observed. However, a three-fold increase in specific activity of the CoA ligase occurred at the time of fungus penetration, 12 hours post-inoculation, in the susceptible disease interaction. A method for the separation of the phenylpropanoids by HPLC was devised.
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Progress 01/01/81 to 12/30/81
Outputs
A system for studying phenolic compound synthesis and disease interactions has been deeloped using the etiolated maize mesocotyl. The technqiue is applicable for differentiation resistance from susceptibility with host differentials to helminthosporium carbonumn, Helminthosporium maydis, helminthosporium turcicum, and Colletotrichum graminicola. Using mesocotyls it was found that H. maydis, in susceptible hosts, blocks the normal expression of resistance. The block occurs up to 100 hr following inoculation with a pathogen which normally induces resistance. The enzyme hydroxycinnamic acid CoA ligase has been identified in maize.
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Progress 01/01/80 to 12/30/80
Outputs
The matrix which protects Colletotrichum graminicola spores form desiccation is a glycoprotein. The matrix invertase and hydrolase are glycoproteins. It is the matrix invertase which offers the greatest protection of spores from loss of viability. Uniform resistance and susceptibility of the corn inbreds 33-16 and Mo940, respectively, has been demonstrated for naturally occuring isolates of C. graminicola and no evidence for the presence of races of the pathogen has been found. The etiolated mesocotyl of corn has been developed for use in studying phenolic compounds synthesized during resistance expression. Anthocyanins serve as markers of resistance expression. In the susceptible response phenol synthesis is blocked (blocking anthocyanins). In resistance anthocyanin synthesis is temporarily and then occurs at an accelerated rate. This indicates that phenol synthesis is redirected in resistance. A new technique has been developed for separation of the
phenylpropanoid phenols by high performance liquid chromatography.
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Progress 01/01/79 to 12/30/79
Outputs
Anthracnose coverage on corn is light dependent. The critical period for illumination was during the day after inoculation. Though lesion coverage was variable host reaction type was not. Data showed that high disease ratings may be obtained when light is limiting (cloudy weather). Colletotrichum graminicola spores are produced with a matrix material. Spore masses stored for up to 4 weeks at 45% relative humidity became dry and powdery but spores retained their viability. When the matrix was removed prior to storage spores lost viability within 24 hr. Addition of partially purified matrix components to washed spores maintained spore viability. Hydrolase and invertase activities in the matrix were not affected by drying of the matrix. In the field spores may survive and be dispersed in dry particulate matter explaining the rapid spread of this disease. Dark grown sorghum seedlings were susceptible to C. graminicola but light grown seedlings were highly
resistant. Plants placed in the light after inoculation showed restricted lesion development and a sharp increase in total phenols. Dhurrin or HCN content was light independent suggesting that the cyanogenic glucoside is not the sole factor in resistance to anthracnose.
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Progress 01/01/78 to 12/30/78
Outputs
At least 13 stress metabolites accumulate in corn in response to fungal infection. The metabolites are phenols and their appearance is directly related to lesion restriction in both resistant and susceptible host-parasite interactions. Both lesion restriction and phenol accumulation are light-dependent. The resistant response of corn to both Colletotrichum graminicola and Helminthosporium carbonum can be reversed to susceptibility by reducing the light intensity under which plants are grown. Similarly, the ability of corn callus to synthesize phenols and to resist fungal infection is directly related to growth of the callus in the light. The matrix of Colletotrichum graminicola contains a non-specific hydrolase complex that is capable of hydrolyzing articifical fatty acid esters of p-nitrophenol, 4-methylumbilliferone and fluorescein. Scanning electron microscopy shows that incubation of the matrix material on the leaf surface results in an etching of the cuticle
surface. The etching factor is heat labile and assumed to be associated with the matrix hydrolase activity.
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Progress 01/01/77 to 12/30/77
Outputs
Ferulic and caffeic acid esters have been shown to accumulate in maize leaves inthe resistance response to Colletotrichum graminicola, Bipolaris maydis, and Helminthosporium carbonum. The non-phenolic portion of the ester has not been identified. The mechanism accounting for compound accumulation is light-dependent. Severity of anthracnose in the field has been correlated with sucrose level in the host tissue. The pathogen, C. graminicola produces unusually high levels of invertase in the acervular spore matrix. The spore matrix also contains a factor which increases anthracnose severity. Spores contain a self-inhibitor. A new bioassay for Bipolaris maydis race T toxin was developed based on inhibition of greening in etiolated primary maize leaves. A positive assay can be made within two hours. KRG-stimulated, MgyRG-dependent ATPase from either T or N cytoplasm corn roots is not affected by B. maydis race T toxin. Maize callus exhibits resistance to C.
graminicola and H. carbonum when grown in the light but not when grown in the dark.
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Progress 01/01/76 to 12/30/76
Outputs
Flavonoid phenolics which accumulate in corn in response to Colletotrichum graminicola have been classified as phytoalexins. Two flavonoids which accumulate are of the flavone class. At least 15 additional phenolics accumulate in response to infection. These include cinnamic acids and complex esters of cinnamic acids. Somatic callus cultures of maize are being used to study cinnamic acid metabolism as a factor of light intensity. Callus is also used for inoculation with Ustilage maydis. Brown midrib mutants of maize were shown to be more susceptible to Fusarium moniliforme than their normal counterparts.
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Progress 01/01/75 to 12/30/75
Outputs
Research has dealt with corn anthracnose caused by Colletotrichum graminicola. Resistance to anthracnose in corn has been determined to result from synthesis of flavonoid phenolic compounds by the resistant host. Two flavonoids accumulate in resistant infected leaf tissue beginning at 40 hours after inoculation. Both compounds are inhibitory to C. graminicola. Flavonoid phenolics do not accumulate in susceptible plants. Extraction of plants for cyclic hydroxamic acids and tests for toxicity of DIMBOA against C. graminicola confirmed that the hydroxamates are not involved in resistance to this pathogen.The synthesis of flavonoids is stimulated by exposure of plants to high light intensity. In addition, high light causes a decrease in lesion size only in resistant plants or in plants termed susceptible but capable of synthesizing phenolics. The rate of this phenolic synthesis is slower than in resistant plants. This information is the first indication that
phenolic resistance compounds are synthesized in corn and will allow us to determine how pathogens "turn on" or "turn off" the ability of a corn plant to accumulate such compounds.
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Progress 01/01/74 to 12/30/74
Outputs
Colletotrichum graminicola which causes corn anthracnose has been found to infect living corn pith tissue as well as leaf tissue. Pith is infected and maceration occurs irrespective of whether the plant exhibits leaf resistance or susceptibility. Hydrolytic pectic enzymes from the fungus account for breakdownof pith from plants with susceptible leaves whereas transeliminative pectic enzymes account for breakdown of pith from plants with leaves resistant to the fungus. Phenolic synthesis after infection is being studied in both resistant and susceptible corns bred. A preformed compound inhibitory to C. graminicola has been found, but not identified, in one anthracnose resistant corn line.
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Progress 01/01/73 to 12/30/73
Outputs
Research has primarily dealt with corn anthracnose caused by Colletotrichum graminicola. More than 200 maize lines have been tested under greenhouse conditions in a search for resistance to the fungus. The response of each host to each of 4 fungal isolates (each isolate from a different geographic location)indicates the presence of races of C. graminicola. The Indiana isolate attacks sweet and dent corn at all stages of host growth and field studies have shown anassociation of disease occurrence with minimum tillage practices. Sweet corn ismore susceptible than dent and is being used in addition to dent to determine the nature of fungal pathogenicity. Although sources of leaf resistance were found in dent corn, no resistance was observed in the sweet corn tested. In addition, experiments have shown that leaf resistance in dent corn can not be used as the only factor for determining total plant resistance since the fungus readily attacks living pith tissue
irrespective of the resistance or susceptibility of leaves. Experiments have shown that the fungus produces at least 5 different enzymes which degrade cell walls and these appear to account for the susceptibility of living pith tissues but appear not to be a major factor in parasitism of leaves. The enzymes are produced both in culture and ininfected corn pith tissue. Studies have also shown that the fungus produces a toxin(s). The specificity of the toxic material is apparently limited to a small group of maize
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