Genetic studies in upland cotton (Gossypium hirsutum L.) I. Heterotic effects

Heterosis has been observed in many self fertilized species, including the cotton plant and it has been the subject of considerable study as a means of increasing its productivity. The objective of the present work was to determine the extension of heterosis over mid-parent, better parent and best parent for seed cotton yield/ha (SCYH) and other agronomic traits, as well as for fiber characters in 15 hybrids from 6 commercial varieties of cotton via., L1 = ‘Deltapine-16'; L2 = ‘Tamcot-SP-21'; L3 = ‘Cabuyare'; L4 = ‘Stoneville'; L5 = ‘Ospino' and L6 = ‘Acala-90-1'. The used statistical design was randomized complete blocks with 21 treatments (6 varieties and its 15 hybrids, excluding reciprocals) and three replications. Variance analysis were carried out and tStudent test was used to determine the differences among means (α = 0.10). There were no significant differences for better parent (HbBPC) in seed index. Significant HbBPC was found for days to blooming initiation; set flowers (SF); boll set; fruitful branches (FB); boll weight and SCYH. For fiber properties, significant HbBPC was found for fiber percentage; fiber length; fiber fineness and fiber strength. Significant heterosis over best parent (HbBPT) was only found for SF, FB and SCYH. Significant HbBPT was not found for fiber properties. Data are also given for heterosis over midparent values. These results demonstrated the presence of Hb for SCYH and other biometrical characters in cotton and the possibility of the agronomic use of this phenomenon in order to increase the productivity in this crop. On the other hand, these results showed that the Hb was mostly negative for fiber quality and that the hybrid L3xL4 with the biggest Hb for SCYH (58.52 %) and 2348.68 kg/ha had a Hb of -8.97 % for the fiber strength, with the smallest value (71 lb/inch 2 ). Those hybrid combinations that present a positive heterobeltiosis for SCYH and fiber quality be selected.