Evaluation of a rapid mass-screening technique for measuring antibiosis to Helicoverpa spp. in cotton cultivars

Abstract

A study of a variety of screening techniques was undertaken to determine their suitability for an antibiosis-enhancing cotton-breeding program. Techniques trialled included 9 different larval bioassays of varying durations on squares, leaves, and seedlings of cotton-using larvae of different ages. Chemical analyses of squares and seedlings, and a field trial to validate laboratory findings, were also conducted. The 'standard' measure of antibiosis in cotton plants, using long-term (8-day) bioassays based on larval weight gain, was found to be unsuitable for mass screening cotton plants for antibiosis to the cotton bollworm, Helicoverpa armigera (Hnbner), in Central Queensland. A 48-h technique using instar VI larvae proved as dependable as the standard, but faster and more energy-efficient, making it more suitable for mass screening. Chemical analyses supported previous findings that terpenoid aldehydes (i.e. gossypol) in cotton produce important antibiotic activity against H. armigera. Highly significant negative correlations were shown between gossypol content of ingested plant material and larval weight gains. In contrast, there was no relationship between condensed tannin content and larval weight gain. The relationships between larval bioassays and allelochemical content of cultivars were confirmed in a field trial.