Progress 10/01/99 to 09/30/04
Outputs
In the final year of this project we concluded a series of experiments: We identified a mechanism to measure the longevity of oospores in soil when those soils are also contaminated with sporangia of this organism. That technique enabled us to learn that soils naturally contaminated with oospores can survive more than two years in diverse soils. As expected, earliness (in the season) of infection and epidemic severity are related to oospore populations in the soil. We were unable to identify different survival rates in different soils. A sampling of isolates of P. infestans isolates from Brazil confirmed that the population structure of this organism in Brazil is very simple: one genotype is found primarily on potatoes and another genotype is found primarily on tomatoes. There is preliminary evidence for the occurrence of ecological races of P. infestans. In an effort to understand host resistance, we analyzed gene expression in tomatoes that had a susceptible or
partially resistant reaction to P. infestans. Several genes that have been associated with resistance were more highly expressed and expressed earlier in a susceptible interaction (on tomatoes) compared to the partially resistant interaction. Thus it seems likely that these genes are not involved in resistance. It seems likely that there is great diversity in the mechanism by which plants respond to pathogens. In a collaborative research project, the relative resistances in a series of potato breeding lines and cultivars were assessed for stability over geographic location and over diverse genotypes of P. infestans. In large part the cultivars and breeding lines ranked similarly in terms of resistance, regardless of geographic location or genotype of P. infestans. As yet unpublished experiments have revealed that sporangia of P. infestans can survive for months in soils. Thus contamination of soil with sporangia early in the season could still lead to tuber infections later in the
season. We investigated the efficacy of various non traditional fungicides (biopesticides, activators of host plant resistance, biocontrols). These were uniformly ineffective in suppressing potato late blight, but had marginal efficacy in suppressing tomato late blight. The more promising of the approaches are being evaluated in combination with resistant tomatoes. We conducted experiments to produce a predictive model of the numbers of sporangia that might be released from a field of infected potato plants. This information will be linked to our previous data concerning sporangia survival during dispersal so that we can construct a predictive system of the numbers of viable sporangia that will survive aerial transit from one field to another. Also we determined that the dynamics of survival of sporangia on leaves (after transit) is very similar to their survival during transit. These data will be used to further refine the numbers of sporangia that might survive transport from
infected plants in one field to initiate infection in plants in another field.
Impacts
Cultivars with 'general resistance' to late blight have been shown to be stable over time and against different pathogen populations. Thus resistant hosts will contribute to a stable disease management. We are close now to predicting quantitatively how disease in one field of potatoes or tomatoes can affect a neighboring field.
Publications
- Reis, A., C. D. Smart, W. E. Fry, L. A. Maffia and E. S. G. Mizubuti. 2003. Characterization of isolates of Phytophthora infestans from southern and southeastern brazil from 1998-2000. Plant Disease 87: 896-900.
- Flier, W. G., N. J. Grunwald, L. P. N. M. Kroon, A. K. Sturbaum, T. B. M. van den Bosch, E. Garay-Serrano, H. Lozoya-Saldana, W. E. Fry and L. J. Turkensteen. 2003. The population structure of Phytophthora infestans from the Toluca Valley of central Mexico suggests genetic differentiation between populations from cultivated potato and wild Solanum spp. Phytopathology 93: 382-390.
- Fernandez-Pavia, S. P., N. J. Grunwald, M. Diaz-Valasis, M. A. Cadena-Hinojosa and W. E. Fry. 2003. Soil-borne oospores of Phytophthora infestans in central Mexico survive winter fall and infect potato plants in the field. Plant Disease: 88: 29-33.
- Haynes, K. G., B. J. Christ, D. P. Weingartner, D. S. Douches, C. A. Thill, G. Secor, W. E. Fry and D. H. Lambert. 2002. Foliar resistance to late blight in potato clones evaluated in national trials in 1997. American Journal of Potato Research 79(6): 451-457.
- Smart, C. D., K. L. Myers, S. Restrepo, G. B. Martin and W. E. Fry. 2003. Partial resistance of tomato to Phytophthora infestans is not dependent upon ethylene, jasmonic acid or salicyclic acid signalling pathways. Molecular Plant Microbe Interactions: 16: 141-148.
- Grunwald, N. J., S. B. Goodwin, M. G. Milgroom and W. E. Fry. 2003. Analysis of Genotypic Diversity Data for Populations of Microorganisms. Phytopathology 93: 738-746.
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Progress 01/01/02 to 12/31/02
Outputs
We evaluated durability of resistance to potato late blight of a selection of 12 such varieties using data from 1960 to the present. Data were extracted from the field notebooks located in the archives of the Mexican National Potato Program in the John S. Niederhauser Library in Toluca, Mexico. There was no trend to indicate that field resistances to potato late blight of Mexican cultivars released between 1965-1999 are not durable. At least two of the cultivars, namely Sangema and Tollocan, have been grown on at least 4-5 percent of the potato acreage and over long periods of time without decay in levels of field resistance. Pedigrees of the 12 varieties indicate that most of the field resistance was introgressed from Solanum demissum. Field resistance might also be derived from commonly grown land-race varieties such as Amarilla de Puebla and Leona. The genetic control of aggressiveness in Phytophthora infestans to tomatoes was investigated by analyzing hybrid
progeny from five different crosses (four F1 crosses and one F2 cross). The parental isolates were all highly aggressive to potatoes, but some had low and others high aggressiveness to tomatoes. Of 225 single oospore progeny tested, 198 were demonstrated to be recombinants on the basis of mating type, allozyme genotype, and (in some cases) nuclear DNA fingerprint. Trisomy for some parental and progeny strains was suggested from analysis of allozyme data. The recombinants were evaluated for aggressiveness to detached leaflets of both tomato and potato. From these assays we suggest that there is a locus with strong influence on tomato aggressiveness, with low aggressiveness dominant Two extant nomenclature systems were reconciled to relate six mitochondrial DNA (mtDNA) haplotypes of Phytophthora infestans, the oomycete pathogen causing late blight disease on potato and tomato. Carter's haplotypes I-a and I-b were included in Goodwin's haplotype A, while Carter's haplotypes II-a and II-b
were included in Goodwin's haplotype B. In addition, haplotypes E and F were included in Carter's haplotype I-b. The mutational differences separating the various haplotypes were determined, and we propose that either haplotype I-b(A) or haplotype I-a(A) is the putative ancestral mtDNA of P. infestans because either can center all the other haplotypes in a logical stepwise network of mutational changes. The occurrence of the six haplotypes in 548 isolates worldwide was determined. Haplotypes I-a and II-a were associated with diverse genotypes worldwide. As previously suggested, haplotype I-b was found only in the US-1 clonal lineage and its variants (n=99 isolates from 16 countries on 5 continents), and haplotype II-b was limited to the US-6 clonal lineage and its derivatives (n=36). In a confirmation of a previous suggestion, the randomly mating population in the Toluca Valley of central Mexico (n=78) was monomorphic for mtDNA haplotype I-a(A). We hypothesize that selection there may
be driving the dominance of that single mtDNA haplotype.
Impacts
We have demonstrated that resistance to Phytophthora infestans in potatoes can be durable. Thus cultivars with field resistance can be used with confidence. Use of such cultivars in the production system will enable reductions in fungicide useage.
Publications
- Smart, C.D. and Fry, W.E. 2001. Invasions by the late blight pathogen: renewed sex and enhanced fitness. Biological Invasions 3: 235-243 (actual is 2002).
- Grunwald, N.J., Cadena-Hinojosa, M.A., Rubio-Covarrubias, O., Rivera-Pena, A., Niederhauser, J.S. and Fry, W.E. 2002. Potato cultivars from the Mexican national potato program: Sources and durability of resistance against late blight. Phytopathology 92: (688-693)
- Gavino, P.D. and Fry, W.E. 2002. Diversity in and evidence for selection on the mitochondrial genome of Phytophthora infestans. Mycologia 94: 781-793.
- Lee, T.Y., Simko, I. and Fry, W.E. 2002. Genetic control of aggressiveness to tomato in Phytophthora infestans. Canadian Journal of Plant Pathology 24: 471-480.
- Grunwald, N.J., Romero-Montes, G., Lozoya-Saldana, H., Rubio-Covarrubias, O.A. and Fry, W.E. 2002. Potato late blight management in the Toluca Valley: Field validation of SimCast modified for cultivars with high field resistance. Plant Disease 86: 1163-1168. Published Abstracts:
- Grunwald, N.J. and Fry, W.E. 2002. Managing potato late blight at the center of origin: integrating durable resistance with a decision support system. Phytopathology 92: S-32.
- Rathbone, M.C., Smart, C.D. and Fry, W.E. 2002. Isolates of Phytophthora infestans that infect Petunia x hybrida and Nicotiana benthamiana also produce INF1. Phytopathology 92: S-145.
- Smart, C.D. and Fry, W.E. 2002. Identification of quantitative resistance in Lycopersicon pennellii to Phytophthora infestans. Phytopathology 92: S-77.
- Smart, C.D., Hodge, K.T., Haney, C.H. and Fry, W.E. 2002. Comparison of elicitin genes in closely related Phytophthora species. Phytopathology S-92: 77.
- Smart, C.D., Restrepo, S., Hart, A., Buell R. and Fry, W.E. 2002. Genomics of compatibility between potato and Phytophthora infestans. Phytopathology 92: S-77.
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Progress 01/01/01 to 12/31/01
Outputs
Component for sustainable management of potato late blight were investigated. Breeding lines and cultivars were evaluated for resistance to late blight in a large field trial conducted near the Thompson Vegetable Research Laboratory near Freeville, NY. The trial contained accessions from the Cornell Breeding Program and also the USDA. Additionally, novel approaches to inducing were also investigated. For the first time in several years, some of the novel approaches to induce resistance appeared somewhat effective. Breeding lines from the Cornell program and the USDA program contained lines with high levels of resistance, and populations from both programs now contain a much higher level of resistance compared to several years ago. The Cornell clone NY 121 continues to maintain its high level of resistance - even against a different strain of Phytophthora infestans the cause of potato late blight. Various fungicides were evaluated for efficacy in suppressing late
blight on tomato. The evaluations were conducted on the susceptible cultivar Atlantic, and again the use of overhead irrigation facilitated a rapid and severe epidemic on unprotected plants. Disease severity was recorded as Area Under the Disease Progress Curve (AUDPC), a statistic that reflects both the earliness and the severity of disease. Unprotected plants had an AUDPC of ca 1600. Several biological approaches had no detectable effect at suppressing disease (AUDPC = ca 1600). Standard fungicides (such as chlorothalonil and mancozeb) suppressed disease very effectively (AUDPC less than 200). A commercial strobilurin that has particular efficacy against early blight (caused by Alternaria solani) was only partially effective against late blight (AUDPC approx. 950).
Impacts
The integration of host resistance to late blight into the management program for potatoes will have important economic and environmental effects. The adoption of some of the highly resistant clones currently in breeding programs will enable significant reductions (up to 75-90%) in fungicide usage.
Publications
- No publications reported this period
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Progress 01/01/00 to 12/31/00
Outputs
This project started in the summer of 2000 so only a small portion of the proposed experiments have been accomplished. We had previously demonstrated that exposure of sporangia of Phytophthora infestans to direct solar radiation was detrimental. Within 50 minutes, most sporangia had been killed by direct sunlight. Experiments were also conducted at a much higher elevation (much greater intensity of ultraviolet radiation) and the survival of sporangia was demonstrated to be even more severely effected by sunlight. Most sporangia were killed within 30 minutes. In additional experiments during summer 2000, we demonstrated that sporangia on leaf surfaces were similarly affected by solar radiation. While sporangia survived longer on leaf surfaces than they do in the atmosphere, exposure to solar radiation was still detrimental. After two hours on tomato leaves, the majority of sporangia had lost viability. Thus it is now clear that solar radiation is the most significant
environmental factor that limits the survival of sporangia of Phytophthora infestans. The epidemiology and management of potato and tomato late blight was investigated in a variety of experiments. We demonstrated the efficacy of various fungicides and identified their appropriate uses in tomato and potato late blight management. Additionally we identified resistances among breeding populations and cultivars of potatoes. The resistance in New York cultivar NY 121 was demonstrated to be at least as effective as half of the recommended fungicide applied to a susceptible cultivar.
Impacts
The appropriate integration of resistant cultivars and fungicides were documented. Some fungicides are appropriate only as protectants, but others can be used to suppress established infections.
Publications
- Ewing, E.E., Simko, I., Smart, C.D., Bonierbale, M.W., Mizubuti, E.S.G., May, G.D. and Fry, W.E. 2000. Genetic mapping from field tests of qualitative and quantitative resistance to Phytophthora infestans in a population derived from Solanum tuberosum and Solanum berthaultii. Molecular Breeding 6:25-36.
- Fry, W.E., Mayton, H.S., Cianchetti, J. and Jaime-Garcia, R. 2000. Update on new late blight strains and their management. New York State Vegetable/Berry Growers Meeting, Syracuse, NY, Cornell Cooperative Extension.
- Fry, W.E., Smart, C.D. and Grunwald, N.J. 2000. Migrations of Phytophthora infestans awaken plant breeders. Phytopathology 90(6):S94.
- Grunwald, N.J. and Fry, W.E. 2000. Analysis of genotypic diversity in population genetic studies should include richness, evenness and diversity. Phytopathology 90(6):S31.
- Grunwald, N.J. Rubio-Covarrubias, O.A. and Fry, W.E. 2000. Potato late-blight management in the Toluca Valley: Forecasts and resistant cultivars. Plant Disease 84(4):410-416.
- Sanchez, G.M., Smart, C.D., Simko, I., Bonierbale, M., Ewing, E.E., May, G., Greenland, A. and Fry, W.E. 2000. Identification of two new R-genes to Phytophthora infestans from Solanum berthaultii. Phytopathology 90(6):S68.
- Cianchetti, J., Mayton, H., Jaime-Garcia, R. and Fry, W.E. 2000. Examination of fungicides for control of potato late blight, 1999. Fungicide and Nematicide Tests 55:194.
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Progress 01/01/99 to 12/31/99
Outputs
The relative resistances of potato clones in the Cornell Breeding Program were assessed in a field experiment during summer 1999. While most clones were quite susceptible to Phytophthora infestans (US-8 clonal lineage), one clone (New York 121) was quite resistant. The level of resistance in this clone makes it attractive for organic growers and home gardeners. Presumably fungicide needed to suppress late blight on this cultivar would be less than half that required for most commercial cultivars. The need for repeated fungicide sprays relative to a single fungicide spray prior to inoculation by P. infestans was assessed in a field experiment. While fungicide was remarkably effective in suppressing disease, weekly applications initiated at least two weeks before arrival of sporangia of Phytophthora infestans tended to be more effective in suppressing late blight than were weekly applications initiated only 24 hours before the arrival of sporangia of P. infestans.
Impacts
Initial results with a breeding line in Bob Plaisted's potato breeding program indicate that it has very high levels of presumably durable resistance. Predictions include the ability for homeowners and organic growers to be able to use this potato genotype successfully without fungicide.
Publications
- No publications reported this period
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