Host resistance in brinjal varieties to the fruits and shoot borer Leucinodes orbonalis Guen ( Lepidoptera: pyralidae)

Abstract

In studies on the host plant resistance in brinjal (Solanum melongena L.) against the shoot and fruit borer, Leucinodes orbonalis Guen. (Lepidoptera : Pyralidae), germplasm materials were screened to identify sources of resistance and an attempt was made to investigate the mechanisms of resistance involved. Forty accessions of brinjal and related species were initially screened in a field trial conducted during the monsoon season of 1982 and these were classified into highly susceptible, moderately susceptible, moderately resistant and resistant classes. The accessions SM-6, SM-56, SM-72 and SM-74 from the highly susceptible group; SM-1, SM-45, SM-48 and SM-71 from in moderately susceptible group; SM-65, SM-68, SM-97 and SM-105 from the moderately resistant group and SM-67, SM-88, S.indicum and S.incanum from the resistant group were further field tested during the summer season, 1982-83 and were evaluated for the levels of resistance. Under artificial infestation of caged single plants of the accessions by the first instar larvae of L. orbonalis, the susceptibility spectrum was found to be similar to the trend noticed in the field trials. In the resistant types, the infestation by L. orbonalis occurred for a relatively shorter duration than in the susceptible ones. In studies on the antibiosis, it was found that the resistant accessions gave rise to larvae and pupae of reduced weights which took longer durations as compared to the highly susceptible accessions. The larval survival was lower in the resistant types. The highly susceptible accessions produced more females than did the resistant line. There was no significant variation in the fecundity of second generation females. In multiple-choice and no-choice tests, the females of L.orbonalis showed a clear preference for the highly susceptible and moderately susceptible accessions for oviposition. Correlation studies revealed that the density of trichomes on the shoot apex, lower leaf surface and lower surface of midribs exerted considerable influence on the ovipositional response of the female moth, the relationship between oviposition and trichome density being of a negative nature. Among the biophysical characters, the higher density of trichomes on shoot apex and lower midrid; lower pith area, lingnified selerenchymatous hypodermis and compact vascular bundles in shoot apex and tight or semi-tight calyx in fruit were found to impart resistance to borer infestation. Positive correlations were detected between the mean percentages of total sugars, crude protein, total ash, nitrogen, potassium and calcium in the fruit on the one hand and fruit infestation on the other. The contents of total ash, calcium, magnesium and iron in shoots on the one hand and shoot infestation on the other were also found to be positively correlated, while silica, zinc, copper and crude fibre contents were negatively correlated with shoot infestation.The implications of the findings have been discussed.