SCREENING TECHNIQUES FOR DOWNY MILDEW RESISTANCE IN GHERKIN CUCUMBERS

Abstract

Downy mildew (Pseudoperonospora cubensis) causes significant losses in cucurbitaceous crops worldwide. P. cubensis isolates were obtained from infected cucumber leaves in Lampang province, Thailand during 2010-2012 in order to determine the downy mildew virulence. The isolates were tested for the presence of highly compatible reactions on specific hosts and categorized as the pathotype 3. This study determined a screening technique that could improve downy mildew resistance of gherkin cucumber lines (Cucumis sativus L.) grown under greenhouse and field conditions including inbred lines, gherkin varieties and hybrid parents of cucumbers. The pedigree method was applied to four generations of gherkin cucumber lines (F2-F5). The results showed an average mildew resistance score for 8 elite gherkin lines from the F5 generation after 40 days of transplanting. The score of the 8 elite lines was less than an average score for other gherkin and commercial cucumber varieties and was equivalent to an average score for downy mildew resistant varieties. On average, these 8 elite lines from the F5 generation had maximum yields as measured by a mean output of 26.9 tons per hectare (more than that of other gherkin cucumber varieties), mean fruits per plant of 32.6 fruits, and a mean weight of each fruit of 19.4 grams. It was concluded that a disease resistance breeding program using this screening technique and its application was successful in controlling and improving gherkin cucumber lines resistance to the downy mildew pathogen, and which led to increased productivity.