Late Blight and Early Blight Resistance from Solanum hougasii Introgressed Into Solanum tuberosum

Late blight and early blight, caused by Phytophthora infestans and Alternaria solani, respectively, are the two most widely occurring foliar diseases of potato in the U.S.A. Resistance to both diseases is necessary if growers are to reduce fungicide applications. Field resistance to late blight has previously been reported in an accession of Solanum hougasii (2n = 72). The putative aneuploid clone E53.61, derived from (S. hougasii x S. tuberosum) x S. tuberosum was obtained from C.R. Brown and crossed with three S. tuberosum clones. Thirty-five hybrid clones were evaluated for foliar late blight resistance at the Russell E. Larson Agricultural Research Center near State College, PA along with the susceptible check 'Atlantic' and for foliar early blight resistance in Presque Isle, ME along with the susceptible check 'Harley Blackwell' for 3 years (2012 to 2014). The experimental design was a randomized complete block design with two to three replications each year. The US-23 genotype of P. infestans occurred naturally and/or was used in inoculations in PA and plants were infected naturally with A. solani in ME. Relative area under the disease progress curve (RAUDPC) values were calculated based on visual assessment of foliar disease four to five times late in the season each year and subjected to statistical and stability analyses. There were significant differences among clones and the clone x environment interaction was significant for both diseases. Of the 35 hybrid clones evaluated for late blight, 16 were more resistant, 7 were more susceptible, and 12 were as susceptible as 'Atlantic'. Of those same hybrid clones evaluated for early blight, 23 were more resistant than 'Harley Blackwell'; the rest were as susceptible. Late blight resistance or susceptibility was independent of the stability of resistance, however, early blight resistance was associated with greater stability. Fourteen clones were more resistant than the check varieties for both late blight and early blight, suggesting that resistance genes for both late blight and early blight have been combined in this genetic material; three of these clones also had high specific gravity and acceptable chip color out of 10 A degrees C storage.