F2 HYBRIDS OF HOST-PLANT GERMPLASM AND COTTON CULTIVARS .1. HETEROSISAND COMBINING ABILITY FOR LINT YIELD AND YIELD COMPONENTS

Although pest-resistant cotton (Gossypium hirsutum L.) germplasm is av ailable, it is generally not equal to adapted cultivars and other elit e germplasm in yield. Cotton F2 hybrids could provide a means to combi ne beneficial traits of high-yielding adapted cultivar (elite) germpla sm with those of pest-resistant germplasms. In the F2 heterosis and co mbining ability were studied for lint yield and the primary yield comp onent boll number as well as for the secondary yield components of lin t percentage and boll weight. These F2 hybrids were produced following a North Carolina Design II mating scheme involving four cultivars as female parents and 16 germplasm lines as male parents. The 64 F2 hybri ds and 20 parents were evaluated in four environments. General combini ng ability (GCA) effects for various parents differed significantly. ' Delcot 344' gave significant, positive GCA effects for all traits stud ied. Significant, positive specific combining ability (SCA) effects we re smaller and less significant than GCA effects. Heterosis of the F2 over the high-parent was observed in six (9% of all F2 hybrids) F2 hyb rids. In the terms of combining ability for yield, the best two parent s were Delcot 344 and 'Coker 315'. The heterosis for yield of F2 hybri ds resulted mainly from increased boll number, boll weight, or a combi nation of both, rather than increased lint percentage. Interaction of GCA and SCA with environments indicated that F2 hybrids must be evalua ted separately in each environment in which they are to be grown. Thes e results suggest that high yielding F2 cotton hybrids can be develope d that may contain acceptable levels of pest resistance.