Quantitative genetic analysis of Sphaerotheca fuliginea sporulation in Cucurbit a pepo

The inheritance mechanism by which summer squash (Cucurbita pepo L.) suppresses powdery mildew (caused by Sphaerotheca fuliginea) sporulation was studied by analysis of the sporulation yield per colony, measured spectrophotometrically at 700 nm. The value of the optical density (LOD) was used as the criterion for the pathogen sporulation. Three breeding lines of summer squash were used: Straightneck powdery mildew resistant (SNP), Benning's Green Tint (BGT) and Sihi Lavan (SLA), each differing in its susceptibility to powdery mildew. Cultivar SNP (resistant) was crossed with SLA (susceptible) or BGT (moderately susceptible) to generate F₁ F₂ and backcross populations. Continuous distribution was observed and joint scaling effect tests indicated that the additive‐dominant model was adequate. Narrow‐and broad‐sense heritability estimates for BGT × SNP were 0.74 and 0.85, respectively, and for SLA × SNP both were 0.79. These results indicate that it should be possible to select C. pepo populations on which S. fuliginea has low sporulation, and which consequently will exhibit quantitative resistance.