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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 objective of this study was to provide a better understanding of the interrelationship between methods of screening for resistance to ear rot, caused by StenocarpeJla maydis. The inheritance of resistance as well as genetic and phenotypic correlation of various selection criteria were investigated. A complete diallel cross of 10 inbred lines, ranging from resistant to susceptible, was evaluated at each of three localities, representative of different environments within the South African maize production area. Plants were artificially inoculated twiCe during the vegetative stages of plant development. Resistance to ear rot was found to be controlled by additive gene effects, with low dominance and interaction effects. Significant genetic correlations existed between various characteristics relating to disease incidence, with high heritability and highly correlated responses. The incidence of rotted ears was the most practical and reliable method to select for resistance. However, the simultaneous use of some measurement of kernel infection was necessary to ensure detection of internal ear infection. An increase in the incidence of upright ears was indicated to result from S. maydis infection, rather than that upright ears predisposed ears to the disease.

Preharvest sprouting resistance is a major breeding criterion in many regions. Screening for preharvest sprouting tolerance is difficult owing to the low heritability of the trait and its tendency to be expressed as a quantitatively inherited character. The screening procedure used currently at the ARC-Small Grain Institute is designed to assess variation of sprouting in intact heads. Five winter wheat cultivars were crossed in a complete diallel fashion. The objectives of the study were to determine the genetic variability of sprouting resistance in the progeny of five winter wheat cultivars, including Elands, a cultivar with excellent sprouting resistance. The preharvest sprouting response and α-amylase activity of these cultivars and their ensuing progeny were compared. Elands was identified as contributing positively towards preharvest sprouting tolerance in various combinations. Elands also had the best overall combining ability for the improvement of sprouting tolerance.

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