Performance of Cottons when Infested with Tobacco Budworm 1

Thirteen germplasm lines of cotton, Gossypiumh irsutum L., including seven cultivars were grown for 3 years with and without tobacco budworm, Heliothis virescens F. There is a paucity of information available on the performance of cotton germplasm when grown under tobacco budworm infestation. Development of insecticide resistance in this insect or a loss of effective insecticides from the market would pose substantial problems for the cotton industry. Objectives of this study were i) to determine the performance of 13 diverse germplasm lines when grown under controlled, uniform levels of tobacco budworm infestation, ii) to identify germplasm useful to breedersf or use in developing cultivars resistant to tobacco budworm, iii) to identify germplasm lines with different levels of resistance useful for studies on how or why cotton germplasm resist tobacco budworm and iv) to develop information useful for improving breeding practices in cotton. Plots were grown on a Leeper silty clay loam, fine montmorilloritic, non-acid, thermic, chromondertic, Haplaquept, 0 to 2%s lope. Infested plots were inoculated with first instar tobacco budwormla rvae five to six times at weekly intervals beginning about the second week of squaring as determinedi n ‘Stoneville 213’. Worm-free plots were sprayed weekly with fenvalerate [cyano(3-phenoxyphenyl)methy4-chloroalpha-(l-methylethyl)benzeneacetate]. Resistance was measured as the ability to resist yield loss when continually infested with tobacco budworm larvae for 5 to 6 weeks. Resistance was identified in ‘Stoneville 506’ and confirmed in PEE DEE 875, PEE DEE 8619 and ‘Tamcot CAMD-E’. Because two are cultivars and are presently being grown, information on them can immediately be put to use. Each of the four germplasms should be useful to breeders as parental lines to increase resistance to tobacco budworm. Regression analyses on one year's data suggest that about 65% of the resistance is associated with early, rapid fruiting. However, additional unidentified factors are also involved.