A comparison of two methods of assessment of maize varietal resistance to the maize weevil, Sitophilus zeamais Motschulsky, and the influence of kernel hardness and size on susceptibility

Fifty-two maize varieties were screened for resistance to infestation by th e maize weevil, Sitophilus zeamais, using assessment methods proposed by Do bie (J. Stored Products Res. 10 (1974) 183-197) and Urrelo et al. (J. Store d Products Res. 26 (1990) 100), The two methods gave similar assessments of maize susceptibility to S. zeamais. The Dobie method is preferred due to t he lower total time required for assessment of relative susceptibility of m aize varieties. The greatest disadvantage of the Urrelo method is the inten sive labour requirements in the early stages of a trial, when numbers of eg gs have to be counted, although it has the advantage that the assessment ma y be terminated upon emergence of the first Fl adult. Two explanatory varia bles, kernel size and hardness, were investigated to determine whether they may be used as indicators of resistance. Results suggested that kernel siz e is the more important in determining resistance to attack by S. zeamais, with large kernels appearing to show greater resistance than small ones. Co ntrary to expectations, of the varieties tested, including local, hybrid an d improved open pollinated (IOP) varieties, the local varieties were genera lly more susceptible. This may be related to kernel size, as all IOPs and h ybrids tested had large kernels, whereas the majority of the local varietie s had small ones. No clear relationship between weevil susceptibility and k ernel hardness could be detected, although there was an indication that dif ferences associated with kernel size varied depending on kernel hardness, N one of the varieties tested showed high levels of resistance to attack by S . zeamais. (C) 2001 Elsevier Science Ltd. All rights reserved.