Interaction of genes and environment conditioning inheritance of stripe rust resistance of wheat
Lewellen, Robert Thomas
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Seedling infection types of four wheat varieties and their F1, F2, F3, testcross, and testcross-F2 distributions were infected with a single unidentified race of Puccinia striiformis and used to study the inheritance of stripe rust resistance genes, their interaction with each other, and with temperature. Two rigidly controlled environment chambers were used, temperature being the important variable. Diurnal temperature profiles with gradual inclines and declines were used which simulated spring and fall conditions, 2 C night/18 C day, and early to mid-summer conditions, 15 C night/24 C day. Wheat varieties P. I. 178383 (ovo) and Chinese 166 (ovo) had dominant genes for resistance which conditioned a ovo infection type. The heterozygote of these factors conditioned a oo to 0 infection type. The double heterozygote conditioned a ovo infection type. In addition, these varieties had minor genes which conditioned 0, 1, 2, and 3 infection types in certain additive combinations. Rego (0 at 2/18 and 3 at 15/24) had a pair of dominant complementary genes which conditioned a 3 infection type at both profiles. However, at 2/18 Rego had temperature sensitive minor genes which conditioned a O infection type in combination with the two complementary genes. Lemhi (4) was considered to be completely void of resistance genes. Distributions of segregating progenies showed a significant interaction with the temperature profile. The minor factors from either P. I. 178383 or Chinese 166 conditioned greater resistance at 15/24 than at 2/18 and had just the opposite response of Rego’s temperature sensitive factors. Combinations of factors from these parents were additive at both temperature profiles. These minor factors were not entirely in common and transgressive segregation was observed for increased resistance. The minor factors were also effective in causing the major factors to condition greater resistance, particularly for the heterozygote of either major gene. The infection types used, ovo, oo, 0-, 0, 1, 2, 3, and 4 were found to have a genetic basis and were good indications of the genotype at the controlled conditions. The infection type distribution for each cross at each temperature was unique as to proportion of different types and range of expression of various factors or combinations of factors.