INHERITANCE AND ALLELISM OF RUSSIAN WHEAT APHID RESISTANCE IN SEVERALWHEAT LINES

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) has caused serious reduction in wheat production in 17 Western states of the Unit ed Stales since 1986. Inheritance of resistance to RWA in seven wheat lines and the allelism of the resistance genes in these lines with thr ee known resistance genes Dn4, Dn5, and Dn6 were studied. The seven re sistant lines were crossed to a susceptible wheat cultivar 'Carson' an d three resistant wheats: CORWA1 (Dn4), PI 294994 (Dn5), and PI 243781 (Dn6). Seedlings of the parents, F-1, and F-2 were screened for RWA r esistance in the greenhouse by artificial infestation. Seedling reacti ons were evaluated 21-28 days after the infestation using a 1-9 scale. The resistance level of all the F-1 hybrids was similar to that of th e resistant parent, indicating dominant gene control. Only two distinc tive classes were present and no intermediate types were observed in t he F-2 population, suggesting qualitative, nonadditive gene action, in which the presence of any one of the dominant alleles confers complet e resistance to RWA. Resistance in CI 2401 is controlled by two domina nt genes. Resistance in CI 6501 and PI 94365 is governed by one domina nt gene. Resistance in PI 94355 and PI 151918 may be conditioned by ei ther one dominant gene or one dominant and one recessive gene. No conc lusion can be made on how many resistance genes are in AUS-VA1-F-3, si nce the parent population was not a pure line. Allelic analyses showed that one of resistance genes in CI 2401 and PI 151918 was the same al lele as Dn4, the resistance gene in CI 6501 was the same allele as Dn6 , and AUS-VA1-F-3 had one resistance gene which was the same allele as one of the resistance genes in PI 294994. One non-allelic resistance gene different from the Dn4, Dn5, and Dn6 genes in CI 2401, PI 94355, PI 94365, and PI 222668 was identified and should be very useful in di versifying gene sources in wheat breeding.