Establishing a high throughput screening method for large scale phenotyping of castor genotypes for resistance to Fusarium wilt disease

Abstract

Castor (Ricinus communis L.) is an important oilseed crop providing raw materials for many industries. Its cultivation is seriously affected by the wilt disease caused by Fusarium oxysporum f. sp. ricini. In India, no cultivar could be released for cultivation without wilt resistance. Breeding for wilt resistance is hampered due to the limitation on number of genotypes that can be screened in a traditional ‘sick plot (field) method’. In the pursuit of establishing a high throughput screening method, we evaluated four different methods of artificial inoculation namely seed soaking, soil drenching, root dip and sick pot in glasshouse condition for their efficiency using a panel of eight genotypes with known disease reaction. The results showed that ‘sick pot method’ was the most ideal for accurate identification of resistance or susceptibility in plants in a short time with relative ease. In order to further validate the results, a large set of 132 castor inbred lines were evaluated in sick pot. Based on days-to-death data of the inbred lines, a scoring system was developed to suitably characterize the degree of resistance. Screening of the same set of inbred lines in the sick field produced similar results but moderate and highly resistant genotypes could not be differentiated suggesting the advantage of sick pot method over field screening. The screening method established and the set of resistant or susceptible inbred lines identified in this study could be of immense use in basic research concerning host-pathogen interactions, molecular genetics and breeding applications in castor.