Sugarcane clones vary in their resistance to sugarcane whitegrubs

Abstract

To determine the extent and type of resistance to sugarcane whitegrubs in clones of sugarcane and some of their wild relatives, pot trials and field trials were carried out. The pot trials tested 405 clones and estimated tolerance effects by differences in the yields of tops, roots, and stubble of infested and uninfested plants and estimated antibiosis effects by differences in the survival and final weights of larvae placed into the pots. Two field trials used a split-plot design, insecticide treated or untreated, to determine tolerance effects on yields of commercial cane and antibiosis/antixenosis effects through differences in the number of larvae in untreated plots. Comparison of pot trials and field trials allowed an estimate of the usefulness of pot trials in estimating resistance to whitegrubs under commercial farming conditions. Both pot and field trials showed that a range of tolerance and antibiosis resistance mechanisms to whitegrub feeding exists within the current sugarcane germplasm and close relatives. Tolerance effects were apparent in the growth of tops, roots, and stubble. Antibiosis effects were apparent on grub survival and grub growth. Some of these tolerance effects are partially correlated with the general vigour of clones, but there are a number of clones that depart from the general relationships for tolerance and antibiosis. These clones would be especially important in any future program to increase the levels of resistance within the breeding gene pool. There was reasonable repeatability of pot-based tolerance levels between pot trials and with results derived from field trials. These results would be best incorporated into the current sugarcane-breeding program through a specific subprogram targetting grub resistance and using recurrent selection with rapid generation turnover. This would require the development of an appropriate screening system and may require 2 stages. The first would need to handle large numbers of clones to discard the least resistant. This could be followed by a more intensive screening (e.g. our pot technique) to identify the most resistant clones. Those identified after the first cycle of selection would then be recombined to produce more progeny and the process repeated. It is likely that several cycles would be necessary to increase resistance to a level that provides an economic protection.