Managing potyviruses in cucurbit crops by host resistance

Abstract

Three potyviruses: Papaya ringspot virus(PRSV), Watermelon mosaic virus (WMV) ,Zucchini yellow mosaic virus (ZYMV) (family Potyviridae: genus Potyvirus) cause major economic damage to cucurbit crops in all States. Zucchini and melon crops are particularly susceptible. PRSV dominates in Queensland and ZYMV in Western Australia. Insecticide applications have little effect on the rapid, non-persistent transmission of these viruses. Altering planting dates and crop hygiene can help but their influence is variable. Host resistance provides effective, economic control. Eighteen zucchini (Cucurbita pepo) varieties were recently assessed for virus resistance in a trial in south-east Queensland. All plants in two replicates were inoculated with PRSV at the cotyledon stage and the two replicates of the same varieties were not inoculated. Plants were assessed for symptom severity, total yields and yields of marketable fruit over five weeks with three harvests/ week. Four varieties were superior to the most widely grown virus tolerant variety in both inoculated and non-inoculated plots. Previous work has shown that varieties with good resistance to PRSV are also resistant ZYMV. Highly resistant zucchini varieties are commercially available and can largely prevent losses from potyvirus. Limitations identified in trial work include only average potential yields from some virus resistant varieties and mild leaf symptoms are not always well correlated with lack of fruit symptoms. Potyvirus resistant watermelon (Citrullus) and squash remain a challenge as no suitable material has been identified in greenhouse and field trials.