Inheritance of okra leaf type in different genetic backgrounds and its effects on fibre and agronomic traits in cotton
Okra leaf (L0L0) cottons confer resistance/non-preference against insect pests. The inheritance of this trait was studied in three cross combinations involving a common okra leaf parent (HRVO-1) with three normal leaf (l0l0) parents (FH-1000, CIM-446 and Acala 63-74). The non-significant χ2 in F2 for leaf shapes in all the crosses fit well against the theoretical monohybrid ratio of 1:2:1 showing incomplete dominance. Observations of 1 okra leaf (L0L0) : 2 an intermediate class of sub-okra (L0l0) : 1 normal leaf (l0l0) were observed in the F2 populations of the three crosses. In the backcross generations with parent- I, ratios of 1 okra leaf : 1 sub-okra, leaf morphologies were obtained. Similarly, in the backcrosses with parent-II, ratios of 1 normal leaf : 1 sub-okra, an intermediate class of leaf shape were observed. The discontinuous variation for leaf shape in F2 generations of three crosses observed in the frequency distribution confirmed the qualitative inheritance for this trait. The incorporation of the gene for okra leaf type had no significant effect on the major fibre quality attributes like fibre length, fibre strength, lint percentage, fibre uniformity ratio and fibre fineness. Number of sympodial branches/plant, number of bolls/plant, boll weight and seed cotton yield/plant principal yield assuring traits showed improvement, with the incorporation of the gene for okra leaf type. The gene for okra leaf type can be incorporated in a genotype that covers the insect non-preference and yield enhancements without increasing number of monopodial branches. The justification for the increase in yield and its components is due to the okra leaf morphology conferring resistance/non-preference against insect pests with reduced leaf area allowing better air flow and maximum sunlight penetration through the leaves of the plant.
Key words: Gossypium hirsutum L, trichomes, inheritance, fibre traits, agronomic traits.