Resistance of sugarcane varieties to smut (

Aims and methods An experiment was established in Australia in 2008 with 34 varieties of sugarcane, to determine disease development over the crop classes, and the relationship between resistance category and yield loss from sugarcane smut. Key results Yield loss was related to incidence and disease severity in different varieties. Susceptible varieties had > 40% smut infected plants in the plant crop whereas little smut infection was observed on intermediate and resistant varieties. Smut disease across all varieties increased from 5% incidence and 7% severity in the plant crop to 46% and 19% incidence and severity respectively in the first ratoon (first regrowth crop) and to 59% and 27% incidence and severity respectively in the second ratoon (second regrowth) crops. Strong negative correlations were observed for smut incidence (r = −0.57) and severity (r = −0.62) with cane yield in the second ratoon crop. For every percent of increase in smut incidence and severity, a loss of 574 kg and 756 kg of cane per hectare were estimated, respectively. Similarly, the losses of tonnes of sugar per hectare were estimated to 96 kg and 128 kg for each 1% increase in smut incidence and smut severity. Conclusion Regression analysis showed that yield loss can be reduced from > 40% for susceptible varieties to < 6% for resistant varieties. Implications A relationship of different resistance categories and yield loss due to sugarcane smut has been established to develop a guide for growers in selecting appropriate varieties for a particular agroclimatic zone.