Susceptibility of Basil Cultivars and Breeding Lines to Downy Mildew (Peronospora belbahrii)

Downy mildew, caused by Peronospora belbahrii, is a new disease of basil (Ocimum spp.) in the United States. In 2009, different basil species, cultivars, and advanced breeding lines of sweet basil (30 in total) were evaluated for susceptibility to basil downy mildew in field trials in southern and northern New Jersey. Popular commercial sweet basil cultivars such as Martina, Nufar, and Poppy Joe were among the most susceptible to downy mildew. Symptoms and sporulation of P. belhahrii on Ocimum xcitriodorum and O. americanum cultivars were present but far less than on most O. basilicum cultivars evaluated. The cultivars Spice, Blue Spice, and Blue Spice Fil were the least susceptible to basil downy mildew with no visible symptoms. Similar results were observed in both field trials. This is the first report of potential resistance in Ocimum spp. to basil downy mildew. Observations from this study show that the development of resistant cultivars may be possible. Selection criteria such as foliar morphology, plant architecture as well as the presence of secondary metabolites are being examined as potential traits for developing downy mildew resistant basil cultivars.