Genetic Variation in PI 294994 Wheat for Resistance to Russian Wheat Aphid

Abstract

The search for resistance genes in wheat (Triticum aestirum L.) is a continuous process in breeding a wheat cultivar resistant to the Russian wheat aphid (RWA), Diuraphia noxia (Mordvilko). Several researchers have obtained different results about how many resistance genes are in PI 294994 wheat. Genetic variation within PI 294994 was studied as a possible explanation for the conflicting results. Twentytwo individual RWA-resistant plants from the PI 294994 wheat accession were selected and crossed to the RWA-susceptible cultivar Carson. The F2 and backcross test for resistance to RWA showed that the number of resistance genes in the original individual plants of PI 294994 was different. In five PI 294994 plants, two dominant, independent genes control the resistance to RWA; in four PI 294994 plants, one dominant gene governs the resistance to RWA; and in two PI 294994 plants, one dominant and one recessive gene appear to confer resistance. In nine PI 294994 plants, F2 segregation data fit either one dominant or one dominant and one recessive gene models. The numbero f resistance genes in the remaining two PI 294994 plants could not be determined; however, the data fit a linked dominant gene model. Furthermore, the data which fit the one dominant and one recessive gene model also fit the linked dominant gene model. Linkage analysis using the maximum likelihood technique indicated that the crossing-over percentage between the two RWA resistance genes was P = 0.21 ± 0.04. Further experiments to clarify different models for explaining the F2 segregation data are underway. This study clearly indicated that results from previous studies on resistance gene number and types in PI 294994 were not in conflict with each other, but were based on different RWA-resistant selections within PI 294994. We are regrouping the original PI 294994 wheat accession into four sub-accessions based on their resistance to RWA.