The segregation ratios for verticillium wilt resistance in PI 215699 suggests that verticillium wilt resistance is a quantitative trait. Additive and dominance genetic variance effects were studied. The F1, F2, F1 B Cr, and F1 B Cs, using the resistant parent (Pr) and the susceptible parent (Ps), PI 215699, and BG. 1668, respectively, were accomplished. The plants were grown in soil temperature tanks with a 25 ± 1C soil temperature, an inoculum level of 2000 microsclerotia of Verticillium dahliae Kleb. per gram of soil, and 18 hours of 250 umol·m-2 · s-1 light. The experiment consisted of four replications with 30 plants per replication for each generation. The seedlings were individually scored 70 days after sowing for an interaction phenotype score (IP) using a scale ranging from 1 to 9 in which 1 = no aerial symptoms and 9 = death. Means, variance, and standard deviations for the percentage of resistant plants (IP = 1) were calculated. A joint three-factor scaling test to estimate the parameters [mid-parent value (m), additive effects (d), and dominance effects (h)] revealed that the data did not fit a simple additive-dominance model. Epistasis was suspected to be present and a joint six-factor model was therefore tested. The joint six-factor model estimates m, d, h, and three epistatic interactions parameters [additive × additive (i), additive × dominance (j), and dominance × dominance (1)]. All epistatic interactions parameters were significant. These results indicate that additive and epistasis effects were involved in the genetic control of verticillium wilt resistance in PI 215699. Broad-sense and narrow-sense heritabilities for percentage of resistant plants in population PI 215699 were estimated to be 0.81 and 0.48 after 70 days of sowing, respectively.
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