|Pavek, J. - RETIRED USDA-ARS|
|Corsini, D. - RETIRED USDA-ARS|
|Lozoya-Saldana, H. - PICTIPAPA UOFMEX CHAPINGO|
|Yilma, S. - OR STATE UNIV CORVALLIS|
|Mosley, A. - OR STATE UNIV CORVALLIS|
Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 27, 2007
Publication Date: July 1, 2007
Citation: Whitworth, J.L., Novy, R.G., Pavek, J.J., Corsini, D.L., Lozoya-Saldana, H., Yilma, S., Mosley, A.R. 2007. Multiple-Site Identification of Potato Parent Clones Conferring High Levels of Late Blight Resistance with a Corresponding Genetic Model for Resistance. American Journal of Potato Research.84: 313-321 Interpretive Summary: Potato seedling minitubers derived from greenhouse crosses have been screened for late blight resistance under heavy disease pressure near Toluca, Mexico. This area is the center of diversity for Phytophthora infestans (Mont) de Bary, the pathogen responsible for late blight. An average of 2500 genetically unique minitubers was planted each year along with cv. Alpha as a susceptible control. Percent defoliation readings were taken on a weekly basis during the growing season in plots without fungicide control. The amount of resistant x susceptible (RxS) and resistant x resistant (RxR) crosses were calculated each year and comparisons on the amount of resistant individuals and families were made across the years. In addition, selection for tuber type was conducted in the same year by planting a replicate of each minituber in Aberdeen, Idaho. At harvest, late blight data collected from Toluca was used to select from these individuals with good agronomics and late blight resistance. Individuals selected at Aberdeen were then screened for tuber resistance at Corvallis, OR. Analysis shows that RxR crosses increase the percentage of resistant individuals, showing that combining resistance from both parents allows for increased selection of resistant types. Parents are identified that give good resistance in RxS and RxS crosses. Comparison of RxS crosses gave data that is used to propose a genetic model for observed segregation in a 1 resistant: 3 susceptible ratio. This ratio is best explained by a gene model in which resistance is conferred by the presence of a dominant allele at each of two loci.
Technical Abstract: Since 1996, the progeny of late blight resistant potato clones have been grown in Toluca Valley, Mexico. This location is the putative center of origin and is the center of diversity for Phytophthora infestans (Mont) de Bary, the oomycete pathogen responsible for late blight, making it an ideal location for screening potato breeding populations for late blight resistance. Up to 3200 individuals from the USDA-ARS, Aberdeen, Idaho potato breeding program were planted each year for evaluation. Each year Percent defoliation readings were taken on a weekly basis through early September. . Comparisons of the number of resistant individuals and their degree of resistance response from resistant x susceptible (RxS) and resistant x resistant (RxR) crosses were made across years in Toluca Valley. Every progeny genotype planted in Toluca Valley was replicated in the field in Aberdeen, Idaho selection of tuber type. This replication allowed for selection of foliar late blight resistant and acceptable tuber type. These selected individuals were screened the following year in the field for tuber resistance at Corvallis, OR. RxR late blight crosses produced 64% resistant individuals compared to 29% RxS crosses. The higher percentage of resistant progeny from RxR crosses demonstrated the usefulness of pyramiding resistance genes from diverse germplasm. Three, late blight resistant parental clones from family A95053 produced progeny having foliar and tuber resistance, and acceptable tuber type. Family A95053 has multiple sources of resistance, that that include S. demissum and S. stoloniferum, from female parent AWN86514-2, and male parent B0718-3 that showed resistance to late blight in Mexico. The segregation for late blight resistance in progeny from specific RxS crosses best fits a 1R:3S ratio. This segregation ratio is best explained by a gene model in which resistance is conferred by the presence of a dominant allele at each of two loci.