Selection of leaf blight-resistant Pelargonium graveolens plants regenerated from callus resistant to a culture filtrate of Alternaria alternata

Abstract

A protocol has been established for the induction of disease resistance in callus cultures of rose-scented geranium, Pelargonium graveolens cv. Hemanti against leaf blight disease caused by the fungal pathogen Alternaria alternata. The callus cultures were raised and maintained on semi-solid Murashige and Skoog's (MS) medium supplemented with 10 mg l⁻¹ Kn and 1.0 mg l⁻¹ NAA. The calli were subjected to various concentrations of culture filtrate (0%, 4%, 8%, 12%, 16% and 20%) obtained from A. alternata. Resistant calli were selected and placed on regeneration medium (MS supplemented with 0.5 mg l⁻¹ BAP and 0.1 mg l⁻¹ NAA). The regenerants were confirmed for A. alternata resistance by exposing their leaves to the same concentrations of culture filtrate as used previously. While the parental wild type demonstrated typical susceptibility, 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 (MS supplemented with 5 mg l⁻¹ Kn and l mg l⁻¹ NAA). The above experiment demonstrated the induction of disease resistance in rose-scented geranium plants at the cellular level. This approach could be successfully exploited in raising new disease-resistant cultivars in geranium against various fungal pathogens.