Assessment of South African bread wheat cultivars for milling quality

English: The objectives of this research were to assess South African winter and facultative bread wheat cultivars for milling quality, to study the effect of genotype x environment interaction on the stability of the wheat quality and to characterise the cultivars for milling performance. Thirteen hard red varieties were planted at six localities throughout the Free Sate at two planting dates, during 1997 to 1999. Betta-DN, Gariep, Molen, SST 367, SST 966 and Tugela-DN were planted at the first planting date. Betta-DN, Caledon, Elands, Gariep, Limpopo, PAN 3235, PAN 3349, SST 124, SST 972 and Tugela-DN were planted at the second date. Material was evaluated for test weight, thousand kernel weight, kernel diameter, kernel hardness, moisture content, vitreous kernels, break flour yield, flour yield, flour colour and flour protein content. Combined ANOVA's for the characteristics was performed over environments. Cultivar differences were determined by means of the least significant difference at individual localities. The analysis indicated highly significant differences among genotypes, environments and GXE interactions, for most of the measured traits. Genotypes contributed significantly to the variance in BFLY, DIAM, TKW and Hl. Environment had a large effect on TW, MOIST, VK, FLY, FCL and FPC. Significant GXE interactions were present for most of the quality traits. Canonical variate analysis was used to differentiate between cultivar groups and indicated that TKW, DIAM, HI, BFLY and TW could effectively differentiate between cultivars. The groups observed with regard to the mentioned characteristics were Gariep with Betta-DN and Molen with SST 966. Tugela-DN and SST 367 were not similar to any other cultivars. At the second planting date, Tugela-DN grouped with SST 124. Betta-DN, Caledon, Elands, Gariep, Limpopo and PAN 3235 formed a group. SST 972 and PAN 3349 were not similar to each other or to the other cultivars. The correlation matrix was performed, to calculate phenotypic relationships between quality traits. TKW had positive correlations with DIAM and these two characteristics indicated positive correlations with MOIST. HI correlated positively to TW and also correlated positively to VK. HI and VK correlated negatively to BFLY. High negative correlations were found between HI and FLY. FLY had positive correlations with BFLY, but correlated negatively with FLC. Stepwise multiple regressions indicated that only small percentages of the variation in TW, HI, BFLY, FLY and FLC could be explained by the other kernel and milling characteristics. HI explained the variation in the TW the most effectively. VK and MOIST could be regarded as the most important variance predictors for HI. Predictors for BFLY were kernel size and HI. These characteristics could define 41.6 to 63.3% of the variation in BFLY. Kernel hardness measurements, HI, BFLY and VK were the most definable for flour yield, together they interpreted up to 50.0% of the variation in FLY. TW explained less than 4% of the variation in FLY; therefore TW is not always reliable in predicting flour extraction. The kernel size explained less than 9.6 to 20.7% of the variation in FLY, illustrating the difficulty of predicting flour yield by indirect calculations. The most important variable in predicting FCL was FLY. AMMI analysis of variance was performed to investigate the influence of the GXE interaction on milling quality. Every locality by year combination was treated as a separate environment. Analysis confirmed differences in genotype performance, that there were varying growth conditions among the localities and the presence of GXE interactions. Interaction effects on TW, percentage VK, FLY, FCL and FPC, were large. IPCA 1 stability scores were compared to the AMMI stability values. Molen was the most stable cultivar at the first planting date. At the second planting date, PAN 3235 and Limpopo were the stable cultivars. Betta-DN, SST 124 and Caledon were also quite stable. Tugela-DN, PAN 3349, as well as the hybrid cultivars SST 966 and SST 972, were unstable with regard to milling quality. Milling performance, as calculated by flour extraction, ash contents and flour colour in various formulas, revealed Gariep and Betta-DN as the high performing cultivars (first planting date), while Molen and Tugela-DN reflected poorer performances. The most effective performing cultivars at the second planting dates were SST 124, PAN 3235, Betta-DN and Limpopo. PAN 3349, SST 972 and Tugela-DN indicated poorer milling performances.