Technique for screening of sugarcane varieties resistant to top borer,Scirpophaga nivella F.

Studies on the resistance to top borer (S. nivella) in sugarcane varieties were made in the plant and ratoon crops. Eight varieties, namely, P. 12235, Co. 1007, Co. 1107, Co. 1148, Co. 1328, G. 12061, CoJ.46 and CoL.9 were grown in 4 replications of 6 rows of 30 meters each. Samples of stalks were taken from 5.0 per cent row length and also four samples of 10 stalks each under the graded incidence of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100.0 per cent from, 400 stalks, cut at random and pooled, in each variety. It turned out that CoL.9 hitherto considered as a susceptible variety towards the top borer, obtained the overall rated value 1, having the least total loss for the sum of characters (stalk length, number of internodes, girth, weight, sucrose and C.C.S.). It was suggested that in top borer endemic areas CoL.9 and P.12235 may be preferred both as plant and ratoon crops. Simple and partial correlations worked out between the per cent of incidence and different loss characters showed that there existed a positive and significant relation between them. The regression coefficient showed a linear relationship between them. The regression equations were also worked out. It was found that from the incidence values alone the relative amount of losses caused in different varieties by the top borer could be confidently predicted. It was concluded that the sugarcane varieties could be screened for resistance to top borer simply by recording the percentage of borer incidence.