Progress in Screening for Resistance to Sugarcane Diseases in South Africa

Methods currently used in South Africa for determining the reactions of new sugarcane clones to smut, mosaic, leaf scald and streak during the process d selection are described and results from recent trials are presented. Resistance screening procedures have been expanded and improved in recent years. The main changes have been the regional location of trials involving the different diseases, screening for resistance to smut and mosaic at earlier stages in the plant breeding selection programme, so that many more new clones are now tested, and the routine use of in~oculation techniques in screening for resistance to smut and leaf scald. Numbers of new clones screened for disease resistance annually are approximately 560 for smut, 200 for mosaic, and 40 for leaf scald and streak. The reactions of advanced clones from all selection sites to the four diseases are assessed at least once before the clones are considered for release. Approximately 50% of the clones tested for response to smut and mosaic prove to be too susceptible for use in areas where these diseases are common. The proportion of clones in the final stages of selection that are resistant to smut has increased recently due to intensive screening at earlier stages in the plant breeding programme.