A temporal genetic analysis of disease resistance genes: resistance to melon vine decline derived from Cucumis melo var. agrestis

Melon vine decline causes severe economic losses to melon crops all over th e world. Two fungi, Acremonium cucurbitacearum and Monosporascus cannonball us, have been reported as the main causal agents of root damage, responsibl e for the decrease in root water and nutrient uptake capacity. However, mel on vine decline aetiology is not completely understood, so screening assays must be conducted under natural infestation conditions. In field assays, t he erratic effect of uncontrolled environmental factors makes the study of the trait's genetics difficult. The percentage of asymptomatic plants score d at individual moments during the infection process in the field is an imp recise indicator of the resistance level of each genotype. The analysis of disease progress curves does allow for the minimization of the stochastic f luctuations caused by environmental factors at various moments in time. Usi ng this analysis the mode of inheritance of the partial resistance to melon vine decline derived from the: accession Pat 81 of Cucumis melo var. agres tis was further studied. Data from the six generations assayed (susceptible and resistant parents. F-1, F-2, and backcrosses BC1 and BC2) were fitted to an additive/dominance model without epistatic effects using a scaling te st. Monogenic control was proposed as the simplest model to explain the dat a. Assuming this simple model, the method of analysis also allowed for the characterization of the incomplete penetrance of resistance, which varies a s a log probit function of the time. Simple genetic control would simplify the use of Pat 81 in breeding programmes aimed at developing commercial mel on varieties with resistance to vine decline.