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Pink Bollworm Resistance, Lint Yield, and Earliness of Cotton Isolines in a Resistant Genetic Background¹

Natural resistance of cotton, Gosspyium hirsutum L., to pink bollworm (PBW), Pectinophora gossypiella (Saunders), may be increased by combining individual resistance traits. The objectives of this study were to determine: (i) the levels of resistance to PBW, as measured by seed damage, in germplasm lines carrying a single morphological resistance trait in a resistant genetic background; (ii) whether combinations of the morphological traits would increase the level of resistance; and (iii) the effects of those morphological traits in the resistant genetic background on lint yield and earliness. All possible combinations of the mutant traits nectariless (N), smoothleaf (S), and okra leaf (L), and of their normal counterparts in a resistant genetic background (AET-5), were grown for 2 yr in insecticide-free environments at Tempe, AZ. Check cultivars were the nectaried, semismoothleaf ‘Deltapine 61’ (DPL-61) and the nectariless, semismoothleaf ‘Deltapine NSL’ (DPL-N). Soil type was a Contine clay loam (fine, mixed, hyperthermic Typic Haplargid). Seed damage, lint yield, and earliness were determined from weekly harvests. The DPL-61 exhibited significantly more seed damage than any other cotton. The AET-5 showed more seed damage than the N, L, NL, and NSL isolines, but not more than the S, NS, or SL isolines or DPL-N. Contrary to expectations, AET-5NL did not have significantly less seed damage than AET-5N or AET-5L. In 1982, when PBW infestations were low, DPL-61 yielded significantly more lint than AET-5 or the isolines (except AET-5NSL). In 1983, when PBW infestations were high, DPL-61 yielded significantly less lint than all but the S isolines. The AET-S and the N, L, and NL isolines were early maturing. The S isolines matured later and yielded as much lint as AET-5 and the other isolines in 1982, but significantly less in 1983. The low yield potential of AET-5 and of the N, L, and NL isolines emphasize that they should be used mainly as sources of multiple resistance to PBW for incorporation into more agronomically acceptable cottons rather than as cultivars themselves.

Key Words: Host-plant resistance • Gossypium hirsutum L. • Pectinophora gossypiella (Saunders) • Bemisia tabaci (Genadius) • Trialeurodes abutilonea (Haldeman) • Bucculatrix thurberiella Busck • Lygus hesperus Knight • Nectariless cotton • Smoothleaf cotton • Okra-leaf cotton • Isolines

² Research geneticist, USDA-ARS, Western Cotton Res. Lab., 4135 E. Broadway Rd., Phoenix, AZ 85040.

Received for publication November 3, 1986.