F2 Hybrids of Host Plant Germplasm and Cotton Cultivars: I. Heterosis and Combining Ability for Lint Yield and Yield Components

Although pest-resistant cotton (Gossypium hirsutum L.) germplasm is available, it is generally not equal to adapted cultivars and other elite germplasm in yield. Cotton F₂ hybrids could provide a means to combine beneficial traits of high-yielding adapted cultivar (elite) germplasm with those of pest-resistant germplasms. In the F₂ heterosis and combining ability were studied for lint yield and the primary yield component boll number as well as for the secondary yield components of lint 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 hybrids and 20 parents were evaluated in four environments. General combining ability (GCA) effects for various parents differed significantly. ‘Delcot 344’ gave significant, positive GCA effects for all traits studied. Significant, positive specific combining ability (SCA) effects were 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 hybrids. In the terms of combining ability for yield, the best two parents were Delcot 344 and ‘Coker 315’. The heterosis for yield of F₂ hybrids resulted mainly from increased boll number, boll weight, or a combination of both, rather than increased lint percentage. Interaction of GCA and SCA with environments indicated that F₂ hybrids must be evaluated separately in each environment in which they are to be grown. These results suggest that high yielding F₂ cotton hybrids can be developed that may contain acceptable levels of pest resistance. Part of a Ph.D. Dissertation of senior author. Contribution of the USDA-ARS in cooperation with the Mississippi Agric. and Forestry Exp. Stn.