Varietal screening host range and control of downy mildew of bittergourd caused by rostow

Abstract

A study was conducted at the College of Horticulture, Vellanikkara, during 1993-95, on varietal screening, host range and control of downy mildew of bittergourd (Pseudoperonospora cubensis (Berk. & Curt.) Rostow). Varieties obtained from the Department of Olericulture were screened for disease resistance and it was found that all the varieties tested were moderately susceptible to the disease. A preliminary screening of 174 genotypes of bittergourd available at NBPGR was conducted during August 1994 and all the genotypes were found to be infected. Only 32 genotypes were moderately resistant to the disease.

Host range studies revealed that P. cubensis from bittergourd can infect other cucurbitaceous crops, such as bottlegourd, pumpkin, cucumber, snakegourd, ashgourd, watermelon and ivygourd. Four fungicides and four plant extracts were tested in in vitro, pot culture and field conditions to find out their effectiveness in reducing downy mildew infection. Among the fungicides, chlorothalonil (0.2%) was found to be the most effective as it gave maximum disease control, maximum yield and highest cost: benefit ratio. Among the botanicals, Ocimum leaf extract (10%) gave maximum reduction of the disease. In crop loss assessment, it was found that the highest CODEX of 60.22 per cent could cause an yield loss of 45.7 per cent under natural condition.