In vitro regeneration of leaf spot tolerant chandrasur (Lepidium sativum L.) from callus resistant to culture filtrates of Alternaria alternata

Disease resistance in callus cultures of chandrasur (Lepidium sativum) against leaf spot disease caused by Alternaria alternata was induced by subjecting the calli raised and maintained on semi-solid Murashige amd Skoog (MS)medium, to various concentrations of A. alternate culture filtrates (0%, 5.5%, 6%, 6.5%, 7% 7.5% and 8%). At higher concentrations (from 8.0 to 10.0 ml l⁻¹) almost all the calli died and total cell mortality was observed. At next lower concentration of 7.5 ml l⁻¹ 13% calli survived. At lower levels of toxic culture filtrates (5.5 ml l⁻¹ and below to 5.5 ml l⁻¹) and also in the uninoculated callus no effect on growth of calli was observed. LD₅₀ value was calculated on the basis of fresh weight of callus when subjected to toxic medium and it was found that at 6.0 ml l⁻¹, 50 per cent callus survived. The leaves of putative resistant clones remained green and viable in the presence of toxin and regenerated shoots directly on the toxin-free regeneration medium.