First and second authors: Department of Life and Earth Sciences, Otterbein College, Westerville, OH 43081; and third author: Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907
This study describes the segregation of genes for resistance to the fungus Puccinia triticina in a cross between partially resistant wheat lines L-574-1 and CI 13227 with two and four genes for resistance, respectively. The objectives of this study were to use parental, F1, F2, and backcross populations to quantify maternal effects, degree of dominance, and transgressive segregation, and to determine whether CI 13227 and L-574-1 share any resistance genes for long latent period or small uredinia. In two experiments conducted in the greenhouse, the uppermost leaf of adult wheat plants was inoculated prior to heading with P. triticina. On days 6 to 21 after inoculation, the number of uredinia that erupted from the leaf surface was counted and used to calculate the mean latent period (MLP). The length and width of five arbitrarily selected uredinia were measured and used to calculate uredinium area. Midparent values, degree of dominance, and broad-sense heritability were calculated for MLP and uredinium area. For experiment A, MLP values for CI 13227, L-574-1, F1, and F2 generations were 12.2, 10.5, 10.2, and 10.6 days, respectively. For experiment B, MLP values for CI 13227, L-574-1, F1, F2, backcross to CI 13227, and backcross to L-574-1 were 12.3, 10.0, 10.6, 10.8, 11.1, and 10.0 days, respectively. The inheritance of long latent period was partially recessive, and no maternal effect was present (P = 0.62 to 0.87 for the comparison of means in reciprocal crosses). Broad-sense heritability for MLP ranged from 0.72 to 0.74, and there was transgressive segregation in the F2 and backcross populations. Uredinia of the F1 generation were slightly larger than uredinia for CI 13227. The inheritance of uredinium size was partially dominant, and no maternal effect was present (P = 0.5 to 0.63). Broad-sense heritability for uredinium area ranged from 0.36 to 0.73 and transgressive segregation was present in the F2 and backcross populations. The results for MLP indicate that lines CI 13227 and L-574 likely share one gene for resistance (based on F1 values) but not two genes (based on the presence of transgressive segregation). CI 13227 and L 574-1 appear to have at least one gene difference for uredinium area. The linear relationship between uredinium area regressed onto MLP was significant (P < 0.001) and r2 values ranged from 0.14 to 0.26. These results indicate that the resistance in CI 13227 and L-574-1 could be combined to create wheat cultivars with greater partial resistance than that possessed by either parent based on MLP or uredinium size.