Thirteen winter and intermediate type bread wheat cultivars were evaluated under dryland conditions over a four year period from 1991 to 1994 and over 120 environments in the Free State province of South Africa. The Additive Main Effects and Multiplicative Interaction (AMMI) statistical model was used to describe genotype-environment (G x E) interaction of yield performance under dryland conditions. In all three relatively homogeneous production regions, viz. Western, Central and Eastern Free State, the AMMI model identified distinct patterns of adaptation. The hybrids and long growth period pureline cultivars generally had superior adaptation to high yield potential conditions, while the short and medium growth period pureline cultivars were better adapted to lower yield potential conditions. The AMMI model indicates that it can effectively summarise patterns of adaptation of winter wheat genotypes and similarities of Free State environments, as well as offer a valuable prediction assessment.
The domestic requirement for wheat in South Africa is approximately 2.8 million tons and annually the shortfall on local production is imported to meet the demand. During the past 25 years two distinct wheat marketing mechanisms characterised the wheat industry, impacting significantly on both research and industry. In 1996 the single channel marketing system through the Wheat Board made way for a liberal marketing environment in which market forces of supply and demand determine price. This refocused most research activities on factors to lower input costs and risks, while increasing the profitability of wheat production. Significant challenges were experienced with much stricter milling and baking quality requirements impacting on not only the development of adapted wheat cultivars for South African conditions, but also on fertiliser and cultivar recommendations, as well as production practices. Minimum tillage, preharvest sprouting, as well as the threat of Russian wheat aphid and stripe rust were some of the pertinent challenges faced during this time. Significant scientific breakthroughs of international importance were made with regard to the physiological and biochemical nature of insect resistance and plant defence as well as the transfer of resistance genes from alien species. This review provides an overview of the most pertinent wheat research undertaken from 1983 to 2008.
Preharvest sprouting significantly reduces the quality of the South African wheat crop. This study classified the preharvest sprouting resistance of 17 South African winter wheat cultivars sampled over a range of typical winter wheat growth environments. Sampling was performed under field conditions and sprouting responses were evaluated under controlled conditions. Variation in sprouting response between cultivars was predominantly genetically determined and varied from 1.7 to 7.4 on a scale from 1 (no visual sprouting) to 8 (fully sprouted). Canonical variate analysis and AMMI analysis, as well as the use of hierarchical clustering of cultivars over environments using the AMMI estimates, identified four distinct groups ranging from resistant to susceptible. The AMMI model was used as it combines the additive main effects of the analysis of variance with the interaction effects of principal components analysis. In general, Betta, and certain cultivars derived from Betta, showed good to moderate resistance to pre harvest sprouting, while the hybrids Caritha and Carol, as well as the purelines Tugela and Tugela-DN, tended to be highly susceptible to sprouting.Die uitloop van koring in die aar lei tot 'n verswakking in kwaliteit van 'n groot gedeelte van Suid-Afrika se oes. Hierdie studie klassifiseer die uitloopweerstand van 17 Suid-Afrikaanse winterkoringkultivars oor 'n reeks tipiese winterkoring-verbouingsomgewings. Monstering is onder veldtoestande uitgevoer en die uitloopreaksie is onder gekontrolleerde toestande bepaal. Variasie in uitloopweerstand is hoofsaaklik geneties van aard en wissel van 1.7 tot 7.4 op 'n skaal van 1 (geen visuele uitloop) tot 8 (ten volle uitgeloop). Kanoniese veranderlike analise en AMMI-analise, sowel as die gebruik van hierargiese groeperings, het vier duidelike groepe ge"identifiseer wat gewissel het van vatbaar tot weerstandbiedend. Die AMMI-model is gebruik aangesien dit die hoofeffekte van die variansie-analise met die interaksie effekte van hoofkomponentanalise kombineer. Oor die algelmeen het Betta en sommige Betta-tipes goeie tot medium weerstand teen uitloop getoon, terwyl die basters Caritha en Carol en die suiwertelende Tugela en Tugela-DN swak weerstand getoon het.
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