Genetic variability for yield and quality characteristics in South African cotton germplasm (Gossypium hirsutum L.)

English: The objective of this research was to study the genetic variability in South African cotton germplasm and to identify superior parental lines for the improvement of yield and quality characteristics. 2 Six parental lines (Irco, Palala, OR27, 2131-2-5, DPAc90 and Sicala) were crossed in diallel fashion. The parents and their F1-offspring were planted in four experiments at two locations, Rustenburg and Loskop, in two successive years, 1997/1998 and 1998/1999. Twenty agronomic and yield characteristics were measured. The data for each characteristic were subjected to a diallel analysis, using the computer program "Agrobase". 3 Significant mean differences were found among the parental lines and their F1-offspring for most of the characteristics measured at both locations, during the two successive years. The only exceptions were SI and LB. On average, Palala and Sicala proved to be the best yielders at Rustenburg, while Irco yielded the best at Loskop. Sicala proved to be the best for FL in both environments, while OR27 was on average the best for FS at both Rustenburg and Loskop. Palala was the best for FU at Loskop, while bath Irco and 2131-2-5 ranked the best at Rustenburg. For the character MC, all the parents were within the acceptable range of 3.5 - 4.5. 4 OR27 proved to be the best combiner for yield and most of the yield components, at both Rustenburg and Loskop. The parental line Sicala proved to be the best general combiner for fibre length, while OR27 was the best general combiner for fibre strength and fibre uniformity at both locations. Parental lines DPAc90 and Irco were the best general combiners for MC at Rustenburg and Loskop respectively. 5 The G.C.A.:S.C.A. ratios were close to unity for most of the characteristics, including yield. Some of the characteristics, such as HC (31.6 - 46.8), GOT2 (1.7 - 17.3), FS (4.6 - 15.7) and FL (2.9 - 14.4) had relatively high G.C.A.:S.C.A. ratios. 6 Extremely high broad sense heritabilities were found for HC (0.92 - 0.98), FL (0.92 - 0.95) and GOT2 (0.77 - 0.93). Extremely high narrow sense heritability was found for HC (0.88 - 0.92), and relatively high values were also computed for FL (0.32 - 0.77), GOT2 (0.42 - 0.87), and FS (0.48 - 0.63). 7 Extremely high significant genetic correlations were computed between SCYP and LYP (0.97), SCYPLT and LYP (0.97), SCYPLT and LYPLT (0.98), SCYP and HC (0.98), LYP and HC (0.97), SCYP and TBF (0.96), SI and U (0.98) and FL and FS (0.97). 8 Relatively high positive correlated response was found between SCYPL Tand GOT2, U, LB, TBF and UHB in bath trials at Rustenburg. In the trials planted at Loskop characteristics like SCYP, SCYPL T, LYP and HC, had relatively high, positive correlated response with most of the other characteristics. High negative correlated response was found between SCYP and GOT, BS, HC and FL in the Loskop trials, while LYP had a negative response with GOT and BS. 9 Mid-parent as well as high or best parent heterosis were highly positive for SCYP and LYP, in most of the crosses. The cross Sicalaxlrco, showed on average the highest amount of heterosis at Rustenburg and Loskop during 1997/98 season. The amount of heterosis for SCYPL Tand LYPL T varies from large negative to large positive values.