Influence of environments on the amount and stability of grain yield in modern winter wheat cultivars I. Interaction and degree of variability

N. Tsenov, D. Atanasova
Abstract. Numerous common wheat varieties have been developed in Bulgaria, which when grown under variable environments, the magnitude of the grain yield is influenced by them. In order to determine the reasons for such variations the effect of the growing conditions on grain yield from the winter wheat cultivars with the highest distribution in production were investigated. The cultivars were investigated during four successive years at twelve different locations in Bulgaria with contrasting environmental components such as soil and climate. The phenotypic response of the cultivars was followed with a focus on the size of the yield and the direction of variation within the group of cultivars as a result of each factor: season, location of growing, genotype, and their complex interactions. The collected data were analyzed with the help of several well-known statistical software, (Statistica 7, Statgraphics XV, Jmp 10), which provided sufficient information on the genotype x environment interaction. Significant differences were found among the investigated cultivars by grain yield regardless of their specific response to the year conditions and the location. The genotype x environment interaction was significantly high and non-linear. This means that under changeable environments the different cultivars react differently and can therefore be grouped according to the grain yield stability and plasticity they demonstrated. This is very clear from the significantly high values of heterogeneity of variation. The principal component analysis showed that the dispersion of grain yield was of three-component type, PC1 being only about 1/3 of the total variation of the character, while PC2 and PC2 formed about 50 % from this variation. Within a wide ecological network of 12 locations in Bulgaria a significant genotype x environment interaction was established for grain yield in four successive years. The direct influence of the investigated factors, through their correlations with grain yield, showed the highest effect of the year (r=0. 476*), followed by the location (r=0.208*), the value of the genotype was the lowest and negative (r=-0. 194*). This normal distribution of the data on grain yield was combined with linear and non-linear type of interaction of the groups of cultivars with the year conditions, the location and their interaction as factors of influence; this made the analysis on the adaptability of each cultivar very difficult.