Genetic Variability Among Glandless Cottons for Resistance to Two Insects1

Abstract

The objective of this study was to determine if genetic resistance to tarnished plant bug (Lygus lineolaris Palisot de Beauvois) and tobacco budworm (Heliothis virescens F.) could be detected among glandless strains of cotton (Gossypium hirsutum L.). We grew 97 glandless strains in the field in two environments. In the first environment, tarnished plant bugs were controlled by five weekly sprayings of an insecticide. In the other environment, tarnished plant bugs were attracted and increased by growing mustard (Brassica juncea (L.) Czern. & Coss), nearby rows. A significant strain ✕ environment interaction for lint yield indicated that there was genetic variability among the glandless strains for resistance to tarnished plant bug. Inspection of the least sensitive strains indicated that many possessed some combination of nectarilessness, hirsuteness, or rapid fruiting ability. These traits and characteristics had been previously found to result in less susceptibility to tarnished plant bugs.First instar tobacco budworm larvae were established on young plants of 99 glandless strains when the third true leaf was expanding. Significant variability was detected for 7‐day average larval weight. Inspection of the 14 strains supporting these smallest larva revealed no readily observable morphological trait that might confer resistance. A second test with the 14 selected strains indicated that the ability of the larvae to develop on these strains was generally lower than on glandless ‘Stoneville 7A’. While four strains did not differ significantly from glanded Stoneville 7A, none of the resistant glandless strains equalled glanded Stoneville 7A in suppressing larval weight. Most of the resistant glandless strains came from one cross of the Louisiana breeding program at Bossier City.These results indicate that significant useful variability for decreased susceptibility to both tarnished plant bug and tobacco budworm is present in glandless cottons.