Downy mildew [Pseudoperonospora cubensis (Berk. & Curt.) Rostov] is an important disease in most cucumber (Cucumis sativus L.) production areas of the world. Resistant cullivars are available, but higher levels of resistance are needed if yield losses are to be avoided. The objective of this experiment was to evaluate all available plant introduction accessions (from the U.S. National Plant Germplasm System), cultivars, and breeding lines (hereafter collectively referred to as cultigens) of cucumber for downy mildew resistance under field conditions in North Carolina. All available cultigens were tested in four blocks (2 yr and two replications) under natural field epidemics of the disease. Mean ratings for downy mildew leaf damage ranged from 1.3 to 9.0 on a 0 to 9 scale. The most resistant nine cultigens originated from the USA, and were primarily adapted cultivars or breeding lines. The most resistant cultigens, for which multiple-year data were available, were Gy 4, ‘Clinton’, PI 234517, ‘Poinsett 76’, Gy 5, ‘Addis’, M 21, M 27, and ‘Galaxy’. The most susceptible cultigens for which multiple year data were available, were P1288995, P1176952, PI 178886, and P1211985. We classified 17 cultigens as highly resistant (1.3–3.0), 87 as moderately resistant (3.3–5.0), 311 as moderately susceptible (5.3–7.0), and 248 as highly susceptible (7.3–9.0) for the cultigens with multiple-year data. No plant introduction accessions were found to be more resistant than the most resistant elite cultivars and breeding lines tested.
The use of trade names in this publication does not imply endorsement by the NCARS of the products named, nor criticism of similar ones not mentioned. The authors gratefully acknowledge the technical assistance of Rufus R. Horton, Jr. This research was funded in part by the North Carolina Pickle Producers Association.