Screening Cucumber for Resistance to Downy Mildew Caused by <i>Pseudoperonospora cubensis</i> (Berk. and Curt.) Rostov.

Abstract

ABSTRACT Downy mildew, a foliar disease caused by the oomycete Pseudoperonospora cubensis (Berk. and Curt.) Rostov. is one of the most destructive diseases of cucumber ( Cucumis sativus L.). Moderately resistant cultivars are available, but yield losses are high without the use of fungicides. Higher levels of resistance are needed to reduce the need for fungicides. The objective of this study was to identify new sources of resistance to downy mildew among Plant Introduction accessions from the U.S. National Plant Germplasm System, elite cultivars, and breeding lines of cucumber. A total of 1300 cultigens were tested in Clinton, NC, and Skierniewice, Poland, in 2005 to 2007 under natural field epidemics. The most resistant and susceptible cultigens were further evaluated in replicated experiments in North Carolina and India in 2007 to 2009. Fungicide experiments were run in 2008 and 2009 to identify tolerance, involving weekly applications to one of two sets of material at a location. Results from the retest study confirmed the results of the initial screening. The most resistant cultigens over all environments were PI 605996, PI 330628, and PI 197088. Cultigens have been found that significantly outperform checks in all resistance traits. High yielding and tolerant cultigens have also been identified that could be used in developing improved cultivars.