Abstract
Rapeseed-mustard crops in general, show low average productivity due to the prevalence of various biotic and abiotic stresses. Among biotic stresses, diseases such as white rust and Alternaria blight are the major contributing factors. Alternaria blight caused by Alternaria brassicae has been reported to cause variable losses in yield. The present study aimed to induce mutations for Alternaria blight resistance/tolerance in Ethiopian mustard and screen the induced mutants through in vivo (detached leaf method) as well as in vitro (cultural filtrate) methods for disease resistance/tolerance in different generations. About 46 mutants in M2 generation were isolated which showed segregation for A. brassicae tolerance. Only 10 mutants showed very less sporulation intensity along with less halo and concentric ring diameter. These mutants were further evaluated under natural field conditions at Kangra to confirm their reaction. Out of these, only two mutants viz., P (4)2 in 80 kR and P13 in 100 kR doses were observed to be moderately resistant/tolerant against A. brassicae (PDI < 25.0%, scale 2). The behaviour of theses mutants was further confirmed by in vitro studies. Both mutants showed pale yellow to light brown and fragile callus in all three concentrations of fungal filtrate. Both fresh and dry weights of calli were maximum in 80 and 100 kR dose-explants in M0 and M4 generations as compared to 50, 60, 70, 90, and 110 kR dose-explants in M0 generation. The in vitro selection could effectively be used to screen genotypes right in M0 generation itself as 80 and 100 kR doses exhibited moderate resistance/tolerance against Alternaria blight both in M0 and M4 generations. Hence, in vitro selection method can be used as an efficient tool for screening mutants dose-wise in initial generations, saving time and laborious field work required to screen mutants in vivo for a minimum of 3 to 4 generations.
Key words: Alternaria blight, brassica, callus, cultural filtrate, in vivo, in vitro, resistance.
