Progress 10/01/03 to 09/30/05
Outputs
Administrative termination, no longer at UCR
Impacts
Administrative termination, no longer at UCR
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
Further progress has been made in isolating and identifying biocontrol agents of P. cinnamomi. The molecular identification of the microorganisms in the suppressive Somis soil, which is the culmination of four years' worth of work, has begun and should be done in six months. Pseudomonas constantinii and P. tolaasii have been identified from New Guinea soil as excellent biocontrol agents of P. cinnamomi. Further evaluation of these organisms will begin pending receipt of USDA permits. Greenhouse evaluation of other potential biocontrol agents, including from commercial sources, has been unsuccessful but is ongoing.
Impacts
Biocontrol may provide an effective, long-term, non-chemical, environmentally acceptable method of controlling Phytophthora root rot of avocado through a combination of cultural methods and application of selected microorganisms. We have provided evidence that excellent control of Phytophtora cinnamomi can be found in suppressive soils and that this suppressiveness can be transferred to other soils. We have developed a method to identify the microorganisms in the soil responsible for the suppressiveness. Several excellent candidates for biocontrol of Phytophtora cinnamomi have been identified.
Publications
- McDonald, V. T. and J. A. Menge. 2004. Microbial suppression of Phytophthora cinnamomi in avocado soils. Phytopathology 94:S68(abst.).
- Menge, J. A. amd McDonald, V. T. 2004. Management of soil microorganisms for the control of Phytphthora root rot. Phytopathology 94: S125(abst.)
- Yin, B., A. J. Scupham, J. A. Menge and J. Borneman. 2004. Identifying microorganisms similar to that of the pathogen: a new investigative approach for discovering biological control organisms. Plant and Soil 259:19-27.
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Progress 01/01/03 to 12/31/03
Outputs
We have identified three sources of soil suppressive toward Phytphthora cinnamomi: 1) Suppressive soils from Southern California, 2) Soils that have experienced an avocado root rot epidemic, and 3) Soils from the region where P. cinnamomi originated, namely Papua New Guinea. Some of these sources are 10-fold more suppressive than the same soils which are fumigated to remove the biocontrol microbes. In some of the soils the microbes and the suppressiveness are transferable to other soils. We are regularly generating new, strong biocontrol candidates such as Rosella sp., Pseudomonas constantinii and Lytobacter mycophilus which are vicious predators of P. cinnamomi in the laboratory. We have created soils with varying level of suppressiveness by heating the Somas CA soil to 21, 45, 60, 75, and 90 degrees. A greenhouse trial was set up with this microbially suppressive soil in which the soil was subjected to this same range of temperatures in order to determine at what
point the suppressive effect disappeared. After takedown, the results showed a gradual decline in the percentage of healthy roots with increasing temperature, which indicated that the suppressiveness was declining with increased temperature. Samples of each soil treatment were taken to the lab, and P. cinnamomi hyphal mats were buried in the soil for one week. One ml of mat suspension was then plated onto various media to check for the predominant fungi and bacteria, which attacked Phytophthora at each temperature. Galactomyces was most common at the lower temperatures, Verticillium and Trichoderma at the higher temperatures and Fusarium was present throughout all temperature treatments. Verticillium, Fusarium and Trichoderma are all known antagonists of Phytophthora but their presence could not be correlated with suppressiveness. According to these results Galactomyces populations correlated well with suppressiveness. Bacterial identification of culture-based organisms and molecular
identification of fungal and bacterial organisms were also done. Molecular examinations of the microbial communities confirmed Galactomyces as a major component of the suppressive soil. Molecular examinations led to the discovery of several other organisms whose populations correlate with suppressiveness. These organisms are related to Chaetomium, Monographella, Fusarium, Tritirachium, Galactomyces, Cryptococcus, Chytridium polysiphoniae and beta-Proteobacteria. Chytridium and Tritirachium are known to parasitize fungi and Chaetomium, Fusarium and Mongraphella are known to suppress Phytophthora. Using new and novel microbial techniques we have identified, isolated and tested our first microbes from suppressive soil. We are now poised to initiate an assembly-line procedure to isolate and test new biocontrol organisms for use against Phytophthora cinnamomi. There probably are several types of soil suppressiveness toward P. cinnamomi and not all of them appear to be of microbial origin.
Pseudomonas putida has been rigorously tested and has proven to be a fair biocontrol agent of Pseudomonas putida.
Impacts
Biocontrol may provide an effective, long-term, non-chemical, environmentally acceptable method of controlling Phytophthora root rot of avocado through a combination of cultural methods and application of selected microorganisms. We have provided evidence that excellent control of Phytophtora cinnamomi can be found in suppressive soils and that this suppressiveness can be transferred to other soils. We have developed a method to identify the microorganisms in the soil responsible for the suppressiveness. Several excellent candidates for biocontrol of Phytophtora cinnamomi have been identified.
Publications
- McDonald V. T., J.A. Menge, E. Pond and M. Crowley. 2003. Suppression of Phytophthora cinnamomi in avocado soils. Phytopathology 93:S129. (Abst.).
- Menge, J.A. and R. C. Ploetz. 2003. Diseases of avocado. P. 35-71. In Diseases of Tropical Fruit crops. R. C. Ploetz ed. CABI Publishng, Wallingford, UK.
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Progress 01/01/02 to 12/31/02
Outputs
We have been testing the EcoSoils field fermentor as a means to continuously apply a biocontrol agent in the irrigation water. The field fermentor which automatically and effectively grows and distributes Pseudomonas putida 06909-rif/nal into the irrigation system at every irrigation. In a mature (50-year-old) commercial citrus orchard covering 2.02 ha, weekly applications of Pseudomonas putida with the field fermentor resulted in soil populations that fluctuated between 2.83 log CFU and 4.35 log CFU/g of soil. Resulting rhizosphere populations of Phytophthora parasitica were significantly reduced in 1999 but not 1997 or 1998. In a newly planted citrus orchard, yearly applications of Pseudomonas putida at the beginning of the irrigation season resulted in high soil populations of Pseudomonas putida that declined rapidly and never reduced the rhizosphere populations of Phytophthora parasitica. When Pseudomonas putida was applied weekly, soil populations increased
throughout the 1997 and 1998 irrigation seasons, reaching a maximum in 1998 and remained high throughout the 1999 irrigation season. Rhizosphere populations of Phytophthora parasitica were significantly reduced in 1998. Yearly applications of the fungicide metalaxyl and the nematicide phenamiphos reduced rhizosphere populations of Phytophthora parasitica in 1997 but not 1998 or 1999. Pseudomonas putida was uniformly distributed throughout the soil profile to a depth of 75 cm in both yearly and weekly applications. When applied through low-volume minisprinklers, Pseudomonas putida was found in aerosols up to 3m away. The effect of repetitive applications of Pseudomonas putida on the resident microbial communities was studied in the newly planted citrus orchard with fatty acid methyl-ester (FAME) profiles and ribosomal intergenic spacer analysis. The data set from FAME was large and very complex, rquiring 23 factors from principle component analysis to explain 91% of the variability in
the data. Effects of field position and season on variation within microbial communities were much greater than the effects of either yearly applications of Pseudomonas putida, weekly applications of Pseudomonas putida or yearly applications of the fungicide metalaxyl and the nematicide phenamiphos. Addition of Pseudomonas putida had only a small but measurable effect on the microbial population. This effect, however, was not correlated well with the populations of Pseudomonas putida. Use of the field fermentor appears to be an effective, safe, cost effective method of disseminating biocontrol agents.
Impacts
The use of the ecosoils field fermentor appears to be a safe effective way to deliver microbial biocontrol agents to the roots of agricultural crops. It dramatically increases the populations and the effectiveness of applying soil-borne biocontrol agents. It overcomes most of the problems surrounding the use of biocontrol agents such as long term survival, presence in an effective state and presence in large numbers.
Publications
- Dirac, M. and J. A. Menge. 2002. High temperatures are not reponsible for lack of infection of citrus roots by Phytophthora citrophthora during the summer, but supressive microorganisms may inhibit infection by P. citrophthora. Plant and Soil 241:243-249.
- Marais. L. J., J. A. Menge, G. S. Bender and B. Faber. 2002. Phytophthora root rot. AvoResearch, California Avocado Commission. 4p. Marais, L. J., J. A. Menge, G. S. Bender and B. Faber. 2002. Avocado stem canker or collar rot. AvoResearch, California Avocado Commission. 4p.
- Menge, J. A., A. J. Downer, K. Steddom and J. Borneman. 2002. Biocontrol of Phytophthora cinnamomi. Proceedings Calif. Conf. Biological Control. Aug15-16. Davis, CA.
- Menge J. A. and L. J. Marais. 2002. Strategies to control Phytophthora cinnamomi root rot of avocado. Subtropical Fruit News 10: 1-3.
- Steddom, K., O. Becker and J. A. Menge. 2002. Repetitive applications of the biocontrol agent Pseudomonas putida 06909-rif/nal and effects on populations of Phytophthora parasitica in citrus orchards. Phytopathology 92:850-856.
- Steddom, K., J. A. Menge, D. Crowley and J. Borneman. 2002. Effect of repetitive application of the biocontrol bacterium Pseudomonas putida 06909-rif/nal on citrus soil microbial communities. Phytopathology 92:857-862.
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Progress 01/01/01 to 12/31/01
Outputs
Two enzyme systems, cellulase (beta-1,4-glucanase) and laminarinase (beta-1,3-glucanase) were added to soil extracts to simulate (in vitro) lytic components found in mulches suppressive to Phytophthora cinnamomi. Concentration ranges of each enzyme were incubated with Phytophthora cinnamomi mycelium, zoospores, zoospore cysts, and zoospore-infected excised roots to evaluate the roles of each enzyme in potential control of avocado root rot disease. Cellulase significantly retarded the development of zoosporangia and chlamydospores when mycelia were incubated in soil extract containing the enzyme at concentrations greater than 10 units/ml. Zoospore production was also reduced by cellulase but not by laminarinase. Laminarinase had little effect on zoosporangia or chlamydospore formation. At high concentrations, laminarinase was consistently more effective at preventing encystment than cellulase. Chlamydospores preformed in root tips were immune to the lytic effects of
all treatments except cellulase at 100 units/ml. Zoospores placed in enzyme solutions and plated on selective media survived high cellulase concentrations and formed colonies, but there were fewer surviving zoospores when laminarinase was present at greater than 10 units/ml. Low concentrations of cellulase stimulated infection of excised roots, however, low concentrations of laminarinase prevented infection. A series of soil samples were taken from mulched and unmulched avocado trees starting at the surface of mulch or soil to a 15cm soil depth, forming a vertical transect. Cellulase and laminarinase enzyme activities were greatest in upper mulch layers and rapidly decreased in soil layers. Enzyme activities against Phytophthora cinnamomi cell walls were significantly greater in mulch than in soil layers. When Phytophthora cinnamomi was incubated in situ at the various transect depths, it was most frequently lysed at the interface between soil and mulch. Roots that grew in mulch
layers were significantly less infected with Phytophthora cinnamomi than roots formed in soil layers. In mulched soil, roots were commonly formed at the mulch-soil interface where Phytophthora populations were reduced, whereas roots in unmulched soil were numerous at the 7.5cm depth where Phytophthora cinnamomi was prevalent. Enzyme activities were significantly and positively correlated with each other, microbial activity, and saprophytic fungal populations, but significantly negatively correlated with Phytophthora recovery. We evaluated a commercial field fermentor as a means of delivering bacterial biocontrol agents through irrigation water. There was no evidence of contamination in 12 hr cultures. It produced 120 liters of inoculum at 500,000,000 CFU/ml after 12 hr fermentations. Ten repetitive applications of Pseudomonas putida yielded soil levels similar to those from a single application at 10-fold greater concentrations. Repetitive applications with a field fermentor may be a
cost-effective method for delivering bacterial biocontrol agents to large acreages.
Impacts
The research above provides answers as to why mulching controls root rot caused by Phytophthora cinnamomi, and allows us to better control this root pathogen. We have also identified a field fermentor machine which produces large amounts of high quality inoculum and delivers it into irrigation water. This machine eliminates many of the problems inherent with the commercial use of fungal and bacterial biocontrol agents and may greatly improve their effectiveness in the field.
Publications
- Marais, L. J., O'Connell, N., Menge, J. A., Adaskaveg, J. E. and Sakovich, N. 2001. A new fungal disease attacking lemons in Tulare, Ventura and Riverside Counties. Citrograph 86:4-5.
- Menge, J. A. 2001. Mulches. P. 650-651. In Encyclopedia of plant pathology. Maloy, O. C. and T. D. Murray. (Eds.). John Wiley and Sons, Inc., New York.
- Menge, J. A. and Marais, L. J. 2001. Soil environmental factors and their relationship to avocado root rot. Subtropical Fruit News 8: 11-14.
- Steddom, K. and Menge, J. A. 2001. Evaluation of continuous application technology for delivery of the biocontrol agent Pseudomonas putida 06909-rif/nal. Plant Dis. 85: 387-392.
- Steddom, K., Menge, J. A. and Borneman J. 2001. The effect of continuous application of a biocontrol bacterium on root rot of citrus and the soil community. Proceedings Biocontrol in a New Millenium: Building for the future on Past Experience. Joint Reg. Biocontrol Conf. Estes Park, Colorado
- Yang, C.-H., Crowley, D. E. and Menge, J. A. 2001. 16S rDNA fingerprinting of rhizosphere bacterial communities associated with healthy and Phytophthora infected avocado roots. FEMS Microbial Ecology 35: 129-136.
- Yin, B., Menge, J. A., Pond, E. and Borneman, J. 2001. An in situ, culture-independent approach to examine substrate competition of soil microorganisms for discovery of biological control agents. Phytopathology 91(6):S98. (Abst.).
- Downer, A. J., Menge, J. A. and Pond, E. 2001. Association of cellulytic enzyme activities in Eucalyptus mulches with biological control of Phytophthora cinnamomi. Phytopathology 91: 847-855.
- Downer, A. J., Menge, J. A. and Pond, E. 2001. Effects of cellulytic enzymes on Phytophthora cinnamomi. Phytopathology 91: 839-846.
- Marais, J., O'Connell, N. V., Menge, J. A. and Adeskaveg, J. E. 2001. Characteristics of Hyphoderma gummosis of lemon trees in California. Phytopathology 91(6):S58. (Abst.)
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Progress 01/02/00 to 12/31/00
Outputs
Infection of avocado seedlings by PHYTOPHTHORA CINNAMOMI in infested soil was decreased by 71% with the addition of gypsum soil amendments in replicated greenhouse experiments. The significant reduction in avocado weight caused by P. CINNAMOMI was largely eliminated by the addition of gypsum. Avocado seedlings grown in gypsum-amended soil were no more resistant to zoospore infection by P. CINNAMOMI than were seedlings grown in unamended sol. Permeability of avocado root membranes, as determined by rubidium exuded from root segments over time, was unaffected by growth in gypsum-amended soil. Drainage was not correlated with root infection of avocados grown in soil infested with P. CINNAMOMI and amended with gypsum. It appears that large reductions in infection of avocado seedlings by P. CINNAMOMI in gypsum-amended soils are not caused by an avocado growth response, increased root resistance, reduced root permeability or improved soil drainage. Sporangial production of
P. CINNAMOMI buried in gypsum-amended soil for two days was reduced by as much as 74% in greenhouse trials. P. CINNAMOMI sporangial volume was reduced an average of 64% in gypsum amended soil. Soil extracts from gypsum amended-soil reduced in vitro sporangial production and volume. Irrigation of buried mycelium with gypsum solutions also reduced sporangial production and volume. Zoospore production and colony-forming units of P. CINNAMOMI were reduced in soil amended with calcium sulfate, calcium nitrate or calcium carbonate. Zoospore encystment or passive movement through soil was not significantly affected by gypsum amendments. We have been testing the EcoSoils field fermentor as a means to continuously apply a biocontrol agent in the irrigation water. The field fermentor effectively, automatically distributes PSEUDOMONAS PUTIDA into the irrigation system at every irrigation. The fermentor automatically produced a clean high-density inoculum in as little as 12 hours. Dilutions of P.
PUTIDA UP TO 1:100,000 effectively colonized soil in greenhouse experiments. In citrus field trials with Phytophthora root rot, P. PUTIDA applied continuously in the irrigation water gave higher populations than single, yearly applications and improved biocontrol of PHYTOPHTHORA PARASITICA comparable to the fungicide metalaxyl. Populations of continuously applied P. PUTIDA increased during the irrigation season, reaching a maximum of nearly 100,000 cfu/g soil. Single applications of P. PUTIDA rapidly declined after each yearly addition. The effects of applications of P. PUTIDA on the resident microbial communities was studied with fatty acid methyl ester profiles (FAME), ribosomal intergenic spacer analysis (RISA), substrate utilization patterns (BIOLOG), and plate counts. With all methods utilized except for plate counts, spatial, seasonal, and yearly effects on variation within microbial communities was much greater than effects of either P. PUTIDA or yearly applications of a
fungicide and a nematicide. Repetitive applications of P. PUTIDA appear to be a safe, cost effective method of controlling Phytophthora root rot of citrus.
Impacts
Gypsum applications act as a weak fungicide and significantly lower the inoculum potential of PHYTOPHTHORA CINNAMOMI in soil. We believe that the EcoSoils field fermenter effectively produced and distributed bacterial biocontrol organisms. Continuous application of biocontrol bacteria have tremendous promise and our bacterial biocontrol agent applied in this way gave increased populations in the soil over the growing season. We have documented reduction in PHYTOPHTHORA PARASITICA populations in the field using this method, while single applications of the biocontrol agent did not reduce P. PARASITICA populations. It appears that the EcoSoils field fermenter is an effective delivery method for biocontrol agents. Furthermore continuous application of biocontrol agents considerably improves their effectiveness.
Publications
- DIRAC, M. F. AND J. A. MENGE. 2000. The effect of carbon source on growth of PHYTOPHTHORA CITROPHTHORA and P. PARASITICA in synthetic media. Phytopathology. 90:S118. (Abst.).
- MENGE, J. A. 2000. PHYTOPHTHORA-induced diseases, BOTRYTIS-induced diseases, Septoria spot, Sclerotinia twig blight. In L. Timmer, S. Garnsey, and J. Graham, eds., Compendium of Citrus Diseases. pg 12-14, 25, 32-33, 35. APS Press, St Paul. MESSENGER, B. J., J. A. MENGE, AND E. POND. 2000. Effects of gypsum on zoospores and sporangia of PHYTOPHTHORA CINNAMOMI in field soil. Plant Dis. 86:617-621.
- MESSENGER, B. J., J. A. MENGE AND E. POND. 2000. Effects of gypsum soil amendments on avocado growth, soil drainage, and resistance to PHYTOPHTHORA CINNAMOMI. Plant Dis. 86: 612-616.
- SINGER, A. C., D. E. CROWLEY AND J. A. MENGE. 1999. Use of an anecic earthworm, PHERETIMA HAWAYANA, as a means for delivery of fungal biocontrol agents. Pedobiologia 43: 771-775.
- STEDDOM, K. C. 2000. The effects of continuous application of the biocontrol bacterium PSEUDOMONAS PUTIDA 06909-rif/nal on Phytophthora root rot of citrus. Ph. D. Diss., University of California, Riverside, CA.
- STEDDOM, K. C. AND J. A. MENGE. 2000. Potential risks associated with inundative bacterial biological control. Phytopathology 90: S74. (Abst.).
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Progress 01/01/99 to 12/31/99
Outputs
Raw yard-trimmings (wood, leaves and grass) were applied to newly planted avocado trees on three different rootstocks at the rate of 0.3 cuM/tree/year in two commercial avocado groves infested with the avocado root rot fungus-PHYTOPHTHORA CINNAMOMI. Mulched trees were compared with unmulched trees in randomized, replicated experiments. Mulch increased yield by 61% and canopy volume by 36% in one orchard. In the second orchard mulch initially reduced yields and canopy volume, but by the end of the experiment yields and canopy volume were no different in mulched trees than in unmulched trees. Root growth was greatly stimulated by mulch in both orchards and was increased as much as 184% compared to the unmulched trees. Mulches were found to change the depth of rooting of avocado trees, since most roots in mulched trees were found in the interface between the mulch and the soil. Effects of the mulch were more dramatic on rootstocks less tolerant to avocado root rot. Root
infections caused by P. CINNAMOMI were very low in the mulch and at the mulch/soil interface but significantly higher in the soil, whether it was mulched or not. Populations of P. CINNAMOMI in the soil were unaffected by mulch applications. Zoospore production by P. CINNAMOMI at the mulch/soil interface was significantly lower than at depths deeper in the soil. Hyphal lysis of P. CINNAMOMI was at a maximum at the mulch/soil interface and it was significantly higher than lysis in unmulched soil. Enzymes, which lysed the hyphae of P. CINNAMOMI, were found to be abundant in mulches but not at 7.5 and 15cm below the mulch or in unmulched soil. Two enzymes which were shown to damage hyphae of P. CINNAMOMI, cellulase and laminarinase, were very abundant in the mulches but were much less abundant in the soil below the mulch and in unmulched soil. We have been testing the EcoSoils Field fermenter, which effectively, automatically grows and distributes microbial agents into the irrigation
system at every irrigation. In an effort to control the citrus root rot pathogen, PHYTOPHTHORA PARASITICA, the biocontrol bacterium, PSEUDOMONAS PUTIDA 06909, was applied once in the spring or continuously with every irrigation. In two field trials continuous application of P. PUTIDA resulted in very high populations of the biocontrol agent (above 104/g of soil). Single yearly applications of P. PUTIDA resulted in high populations immediately following application, but the populations declined precipitously. Populations of P. PARASITICA were significantly reduced 95% by a yearly application of the fungicide metalaxyl and the nematicide fenamiphos compared to the untreated control. At two field locations, continuous application of P. PUTIDA significantly reduced populations of P. PARASITICA. Reductions were as high as 72%. The single yearly applications of P. PUTIDA did not significantly reduce populations of P. PARASITICA. Yields of citrus fruit were unaffected by biocontrol or
chemical treatments.
Impacts
We have shown that applying mulch for controlling avocado root rot is a highly effective process. Nearly all avocado growers who are replanting PHYTOPHTHORA CINNAMOMI infested groves now use this method. We believe that the EcoSoils Field fermenter effectively produced and distributed bacterial biocontrol organisms, which reduced PHYTOPHTHORA PARASITICA populations in the field.
Publications
- Downer, A.J., Menge J. A, Ohr H., Faber B. A., Mckee B. S., Pond E. C., Crowley M. G. and Campbell S. D. 1999. The effect of yard trimmings as a mulch on growth of avocado and avocado root rot caused by Phytophthora cinnamomi. 4th International Avocado Congress, Michoacan, Mexico (Abst.).
- Graham, J. M. and Menge J. A. 1999. Root diseases. In Citrus health management. L. W. Timmer and L. D. Duncan (eds.). APS Press. St Paul MN. 197p.
- Menge, J. A., Faber B. A., Downer J. A. and Crohn D. 1999. Use of yard trimmings and compost on citrus and avocado. California Environmental Protection Agency, Integrated Waste Management Board. Pub. no. 443-99-010.
- Steddom, K.C. and Menge J. A. 1999. Continuous application of the biocontrol bacterium. PSEUDOMONAS PUTIDA 06909, improves biocontrol of PHYTOPHTHORA PARASITICA on citrus. Phytopathology 89(6):S75(Abst.).
- Yang, C. H., Crowley D. E., and Menge, J. A. 1999. Microbial community structure of Phytophthora infected and non-infected avocado roots. Phytopathology 89(6):S87(Abst).
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Progress 01/01/98 to 12/01/98
Outputs
Mulches added around the base of avocado trees infested with PHYTOPHTHORA CINNAMOMI resulted in increased microbial activity. Wood decay organisms which produce cellulose and laminarinase enzymes were prominent among these organisms. Activity of these enzymes in the mulch was positively correlated with microbial activity and fungal populations, but negatively correlated with recovery of PHYTOPHTHORA CINNAMOMI. Cellulase was found to dramatically reduce inoculum of P. CINNAMOMI, while laminarinase blocked infection by zoospores at the root. Rooting by avocado in mulched trees was much greater than in non-mulched trees. The application of gypsum retarded P. CINNAMOMI infection potential, reduced disease symptom frequency and increased avocado growth and rooting, but not yield. Calcium amendments added to an avocado grove can improve soil permeability, root growth, fruit yield and reduce root rot when the soil is poorly drained and infested with P. CINNAMOMI. It appears
that the gypsum acts as a weak fungicide and inhibits the amount of sporangial formation as well as sprorangium size. The EcoSoils Field Biofermenter was used to continuously apply the biocontrol bacterium PSUDOMONAS PUTIDA, to two citrus field sites. The biofermenter produced clean inoculum up to one billion cfu/gm and distributed it in irrigation water to the trees. Soil populations of the bacterium increased to 50,000 cfu/gm when applied continuously (once/week), while populations of the bacterium decreased to near zero when applied only once.
Impacts
(N/A)
Publications
- DOWNER, A.J. 1998. Control of avocado root rot and PHYTOPHTHORA CINNAMOMI Rands in mulched soil. Ph.D. Dissertation, University of California, Riverside, 206 pp.
- LEE, S.-W., J.A. MENGE, and D.A. COOKSEY. 1998. Cloning genes expressed during colonization of fungal hyphae or citrus root tips by PSEUDOMONAS PUTIDA. Phytopathology 88:S52-53 (Abst.).
- STEDDOM, K.C. and J.A. MENGE. 1998. Continuous application of the biocontrol bacterium PSEUDOMONAS PUTIDA 06909, increases soil populations over a single application. Phytopathology 88:S85 (Abst.).
- MESSENGER, B.J., J.A. MENGE, C. AMRHEIN and B. FABER. 1998. The effects of calcium on avocado growth and root health. Calif. Avoc.
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Progress 01/01/97 to 12/01/97
Outputs
Eighteen different types of mulch were investigated for their protective effect against the infection of citrus seedlings by PHYTOPHTHORA PARASITICA and PHYTOPHTHORA CITROPHTHORA in the greenhouse. Most of the mulches were effective in reducing seedling infection. The use of yardwaste mulch bioenhanced with TRICHODERMA HARZIANUM or GLIOCLADIUM VIRENS as a biocontrol agent was more effective in controlling diseases caused by PHYTOPHTHORA than was mulch alone. The propagule densities of PHYTOPHTHORA were significantly decreased when the potting soil in which citrus seedlings were grown was amended with mulch infested with the biocontrol agents. Mulch significantly reduced the number and motility and viability of PHYTOPHTHORA zoospores. The amendment of soil with mulch or with bioenhanced mulch significant increased fresh weight, root fresh weight, plant height, root length and root health. The Ashburner method of suppressing avocado root rot was developed in Australia
and consisted of adding organic matter and dolomite as a thick mulch around the base of avocado trees. The mechanisms by which the Ashburner method suppresses avocado root rot have never been elucidated. The effects of the Ashburner method were found to increase the Deuteromycete population, microbial activity and avocado root growth in the upper layer of soil. PHYTOPHTHORA CINNAMOMI populations were significantly reduced by the Ashburner method. In-situ cellulose and 1,3 B-glucanase produced by wood decay fungi degraded the hyphae of PHYTOPHTHORA CINNAMOMI,.
Impacts
(N/A)
Publications
- MENGE, J.A. and S. NEMEC. 1997. Citrus. IN: Soilborne Diseases of Tropical Crops, R.J. Hollocks and J.M. Waller (eds.), CAB International, Cambridge. Pgs. 185-226.
- DOWNER, A.J. and J.A. MENGE. 1997. An enzymatic method for biological control of PHYTOPHTHORA CINNAMOMI Rands using mulch. Phytopathology
- EL-HAMALAWIZ, A. and J.A. MENGE. 1997. Effect of mulch and biocontrol agents on the control of PHYTOPHTHORA diseases of citrus.
- MENGE, J.A. 1997. Understanding the Ashburner method for suppressing root rot of avocado. Am. Soc. Phytopath., Annual Meeting, Rochester,
- MESSENGER-ROUTH, B.J. 1996. The effects of gypsum soil amendments on Phytophthora root rot of avocado. Ph.D. Dissertation, University of California, Riverside. 106 pgs.
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Progress 01/01/96 to 12/31/96
Outputs
The sugary exudate appearing on bark lesions of avocado after infection with PHYTOPHTHORA CITRICOLA, a canker pathogen of avocado, contained viable oospores and hyphal fragments of the pathogen both in the field and in the greenhouse. This sugary exudate was a source of inoculum and dispersal of the pathogen within and between avocado plants. Spraying water onto lesions moved inoculum from the sugary exudate to wounds below. Water from sprinkler irrigation washed propagules into soil around the plants. Viable propagules of PHYTOPHTHORA CITRICOLA were identified in the feces of snails that had fed on infected bark tissues. When these snails were moved to healthy plants, they made wounds on succulent tissue, and also transmitted infectous propagules to wounds on avocado stems and to the soil. Control strategy for the avocado stem canker disease should consider control of these vectors. In previous studies bioenhanced yardwaste (a mulch colonized with biocontrol agents)
showed the ability to suppress populations of PHYTOPHTHORA CINNAMOMI, resulting tin decreased root rot of avocado trees. Organic matter from the mulches was shown to stop or inhibit zoospore activity of P. CINNAMOMI. Bioenhanced mulches resulted in an average of 20% aborted P. CINNAMOMI sporangia. All mulch treatments enhanced soil microbial activity, some increased CO2 levels, but none could be correlated with increased fungal lysis.
Impacts
(N/A)
Publications
- COSTA, J. L. da S., MENGE, J. A., and CASALE, W. L. 1996. Investigations on some mechanisms by which bioenhanced mulches can suppress PHYTOPHTHORA root rot of avocado. Microbial Res. 151:
- COSTA, J. L. da S., and MENGE, J. A. 1996. Mechanisms of soil suppression to PHYTOPHTHORA CINNAMOMI by using bioenhanced mulches. In : Congresso Latino American de Ciencia do Solo, 13, sessao 3, Aguas de Lindoia, S. P. Brazil, CD ROM 1, BICA Producoes.
- COSTA, J. L. da S. AND MENGE, J. A. 1996. Use of bioenhanced mulch for the control of avocado root rot. Fitopatologia Brasileira 21:
- EL-HAMALAWI, Z. A. and MENGE, J. A. 1996. The role of snails and ants in transmitting the avocado stem canker pathogen, PHYTOPHTHORA CITRICOLA. J. Amer. Soc. Hort. 12: 973-977.
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