Abstract
Since 2008, 11 races of Phytophthora capsici have been identified in New Mexico based on their reactions to a set of host differentials, the New Mexico Recombinant Inbred Lines (NMRILs) developed by the Chile Pepper Breeding Program at New Mexico State University. The objective of this study was to appraise the current race structure of 13 isolates of P. capsici newly collected from chile pepper fields in New Mexico. Of the 13 isolates, 12 were identified as new races. Race 25 (isolate PWB175) was the most virulent isolate, and showed virulence that was higher than that of race 1 (PWB24), which is widely used as a highly virulent race for resistance testing of chile peppers in the United States, and was considered as a potential risk for chile pepper production in New Mexico. Of the 17 NMRILs tested, only 7 were needed for the identification of the 12 new races. The NMRILs are genetically stable including their disease reactions, and hence, are invaluable as P. capsici race differentials. A resistance index that ranges from 0 to 1 with 1 being resistant to all isolates was developed in this study. Among all the NMRILs evaluated, one NMRIL (NMRIL-R) had a low resistance index of 0.17, demonstrating its susceptibility to most of the isolates, while other NMRILs (A, B, F, O, and Z) showed medium to high levels of resistance to the P. capsici evaluated with the range of resistance index from 0.75 to 0.89. The NMRILs with a high resistance index can be a good source of resistance for chile pepper breeding programs. The results of this study prove that multiple races of P. capsici can exist in a single production field and plant breeders must be cognizant to breed for more than one race in a given production location. Accepted for publication 3 December 2015. Published 17 December 2015.
Published Version
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