Screening of cauliflower (Brassica oleraceaL. var.botrytisL.) germplasm for resistance to downy mildew [Hyaloperonospora parasiticaConstant (Pers.:Fr) Fr.] and designing appropriate multiple resistance breeding strategies

Abstract

The present study screened a large range of cauliflower (Brassica oleracea L. var. botrytis L.) germplasm for resistance to downy mildew [Hyaloperonospora parasitica Constant (Pers.:Fr) Fr.] and observed the progress of the disease in order to design suitable breeding strategies. Pot experiments using artificial inoculation were conducted under a climate favourable to the disease, and the percentage disease index (DI) was measured 10, 20, and 30 d after inoculation (DAI). Of the 190 genotypes screened, seven were highly resistant (1 < DI ≤ 10), 21 were moderately resistant (10 < DI ≤ 25), 51 were moderately susceptible (25 < DI ≤ 50), 95 were susceptible (50 < DI ≤ 75), and 16 were highly susceptible (75 < DI ≤ 100). The seven most resistant genotypes were BR-2, CCm, 3-5-1-1, CCm-6, CCm-5, MGS-2-3, and cc-12. The overall mean DI value increased from 45.2% at 10 DAI to 58.5% at 30 DAI. Among the genotypes screened, the incidence of downy mildew ranged from 4.5 – 84.6% at 10 DAI, 5.5 – 92.0% at 20 DAI, and 6.0 – 98.8% at 30 DAI. Different stages of plant development showed a strong positive correlation for downy mildew reaction in the genotypes tested. Genotypes identified as resistant can be used as donors to develop multiply-resistant varieties of cauliflower.