Inheritance of resistance to papaya ringspot virus type W in hybrids between Cucurbita ecuadorensis and C. maxima

Abstract

Papaya ringspot virus type W (PRV-W) causes foliar mosaic, deformed fruit and reduced yield in crops of Cucurbita maxima cv. Queensland Blue in Queensland. Cucurbita ecuadorensis is highly resistant to PRV-W. Using crosses between these 2 cucurbits we studied inheritance of resistance to PRV-W in mechanically inoculated parental, F1, F2, backcross and inbred backcross populations under glasshouse and/or field conditions. Disease severity was assessed on each plant as the proportion of the young leaf area which was chlorotic. Inheritance of resistance, following inoculation of cotyledons with either of 2 isolates that differed in the severity of symptoms produced, was most consistently described as polygenic. Analysis of means of generations indicated additive gene effects were predominant. However simpler inheritance could not be entirely discarded as a 13:3 digenic model based on epistasis and modifiers described some distributions. No strong associations existed between high resistance to PRV-W and undesirable characteristics so that transfer of high levels of resistance from C. ecuadorensis to commercially acceptable lines of C. maxima should be possible.