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.
A Verticillium wilt-resistant population of pepper (Capsicum) is being developed from the USDA P.I. 215699 accession. Three selfing cycles with disease screening and selection have been done. The disease screen was conducted at a soil temperature of 25 ± 1°C and at an inoculum level of 2000 microsclerotia per gram of soil. Sixty days after inoculation, individual plants were scored using an interaction phenotype scale (IP), ranging from 1 to 9, where 1= no aerial symptoms, and 9=death. Plant shoot height was also measured. Even after three selfing cycles, P.I. 215699 segregates for Verticillium wilt resistance. The percentage of resistant plants at S3, is 75%. Another cycle of selection (S4) was done and the progeny are being tested. The S4 progeny data, interaction phenotype, shoot height, and percentage of resistant plants, will be analyzed by using standard analysis of variance followed by appropriate means separation. An analysis of correlation for shoot height by interaction phenotype variables will also be conducted.