Evaluation of Cultivars, Germplasm Lines, and Species of Gossypium for Resistance to Biotype “B” of Sweetpotato Whitefly (Homoptera: Aleyrodidae)

Abstract

We evaluated 19 cultivars, germplasm lines, and species accessions of cotton and wild relatives, Gossypium spp., in a field, plot experiment for resistance to biotype “B” of the sweetpotato whitefly, Bemisia tabaci (Gennadius). We collected leaf samples on eight dates from 9 June to 14 September and counted eggs and nymphs. Egg and nymph numbers were <1 per g of leaf weight through June, then began to increase rapidly, reaching 5,100 eggs by mid-August and 2,000 nymphs by mid-September. The rate of increase in Arizona wild cotton, G. thurberi Todaro, was significantly slower and numbers of eggs and nymphs were significantly lower than in the two upland, G. hirsutum L., control cultivars ‘Deltapine 50’ and ‘Stoneville 506’. The 19 cotton entries were divided into four leaf pubescence classes: glabrous, moderately pubescent, pubescent, and highly pubescent. Although no differences in numbers of eggs were obselved among the pubescence classes, the glabrous entries averaged fewer nymphs than the moderately pubescent or pubescent entries, but not fewer than the single highly pubescent entry, G. raimondii Ulbrich. The control upland cultivars, three upland germplasm lines, and the single G. barbadense L. cultivar ‘Pima S-6’ wilted, defoliated, and opened bolls prematurely because of extreme sweetpotato whitefly pressure. In spite of very high numbers of insects, none of the other entries except G. raimondii showed visible wilting and defoliation.