RAPID SCREENING TECHNIQUE FOR ALTERNARIA BLIGHT RESISTANCE IN INDIAN MUSTARD Brassica juncea L USING COTYLEDONARY LEAF METHOD
P.D. Meena, S.J. Jambhulkar, R. Gupta, H.S. Meena, D. Singh
Alternaria blight (AB) caused by Alternaria brassicae (Berk.) Sacc. is a devastating disease of oilseed Brassicas all over the world, and responsible for significant seed yield losses up to 47%. No reliable, resistant germplasm is available to develop AB resistant cultivars. Various screening techniques have been reported so far, but cotyledonary leaf method is not yet reported. Three methods were tested using one susceptible cultivar (Varuna): inoculation of seed, inoculation of cotyledons, and inoculation of both seed and cotyledons. Fungal conidia were inoculated directly onto the seedlings with 1.5x105, 2.5x105, 4x105 and 5x105 conidia ml-1 concentrations for standardization. Percentage AB severity increased with the increase in conidial concentration, therefore the highest concentration was used for final screening. Among the three screening methods, inoculation of both seed, and cotyledon method was found highly effective where mean AB severity on cotyledon was 84.6% in comparison to 49.3% in the inoculation of seed and 62.5% in the inoculation of cotyledon methods. The technique was validated by screening susceptible and putative tolerant genotypes. The severity of AB was 54% of susceptible cultivar and 16.4%-21.2% of tolerant genotypes. The conidia number per microscopic field was 21.5 in putative tolerant and 43.5 in susceptible genotypes. Thus, in vitro screening of AB using inoculation of both seed and cotyledon method was found most effective and could be used for rapid screening in early stages of plant growth. A new 0-7 rating scale was also devised to observe the AB pathogen interaction phenotype at the cotyledonary stage of oilseed Brassica.