The Relationship between Extent of Colonisation by Leifsonia Xyli Subsp Xyli and Yield Loss in Different Sugarcane Varieties

Large-scale yield trials have traditionally been used to rate the reactions of released sugarcane varieties to ratoon stunting disease (RSD). These trials are time-consuming and require large tracts of land and are therefore not suitable for incorporation into a routine programme of disease screening of new genotypes. Using a tissue blot-enzyme immunoassay (TBIA) to determine the percentage of colonised vascular bundles (CVB) in RSD-infected stalks, it is possible to estimate both the incidence of infection and likely severity of the disease. In previous work, the ranking of a number of released varieties for their reaction to RSD using TBIA has correlated well with estimates of yield loss in field trials, but it was necessary to confirm these findings in one trial comparing both methods of variety evaluation. A good correlation between yield loss and percent CVB in six varieties, N12, N14, N16, N27, N29 and N35, was obtained from the results of a rainfed field trial conducted at Mount Edgecombe. Using both methods of varietal assessment, N35 and N27 were found to be the most resistant of the varieties tested while N14 was the most susceptible. The results from this study indicate that the TBIA can provide an effective and more efficient method for evaluating varieties for their reaction to RSD and that it has potential for application in the disease screening programme at SASEX.