Abstract
The levels of acid invertase (Al) and neutral invertase (NI) activity in the stalks and leaves of eight sugarcane cultivars differing in susceptibility to yellow spot disease were determined in plant and first ratoon canes. The activities of AI and NI in 46-75-week-old canes were 25-71 % lower in resistant (R) cultivars than in moderately resistant (MR) and susceptible (S) cultivars. The differences in invertase activity between the cultivars were detected before and after the onset of yellow spot infection. In many of the assays there was a highly significant positive correlation between invertase activity level and yellow spot susceptibility. Multiple correlation between yellow spot susceptibility and Pol percentage cane and invertase activity at various stages of growth was also significant. Al and NI activities of the leaves of the R cultivars in some of the assays were significantly lower than those of the MR and S cultivars, but in other assays, the results were variable. The results of this study on a limited number of cultivars show that cultivars with high levels of invertase activity and low pol percentage were more susceptible to yellow spot. It was suggested that the low invertase activity may contribute to the resistance of some cultivars to yellow spot because of the reduced availability of reducing sugars in these cultivars.
