Comparison of parametric and non-parametric methods for analysing genotype x environment interactions in safflower (Carthamus tinctorius L.)

Genotype x environment interaction (GEI) is a major factor in the development of stable and high-yielding safflower cultivars under rain-fed conditions. In order to quantify GEI effects on the seed yield of 17 safflower genotypes and to identify stable genotypes, multi-environment yield trials (multi-environment trials (MET)) were conducted for four Consecutive years in 33 different environments (year-location combinations) during 2003-06. The results indicated that GEI was significant using the Hildebrand (1980) procedure for non-crossover interaction (no change in genotypic rank) and by the Azzalini & Cox (1984) and the De Kroon & Van Der Laan (1981) tests for crossover interaction (change in genotypic rank). The rank-interaction was not significant when assessed using the Bredenkamp (1974) method. Fifteen univariate stability methods measuring different aspects of stability were used to determine stable genotypes. A principal component analysis based on rank correlation matrix separated those methods based on a dynamic concept of yield stability (change in genotypic performance corresponds to the predicted level for each environment) from those which are based on a static one (the lowest changes in genotypic performance across environments). The methods could be grouped into three distinct classes: (i) those which were associated with yield level and the dynamic concept of stability; (ii) those which were associated with environmental variance, which represents static stability; and (iii) those which were grouped with non-parametric stability statistics, which also represent static stability. The superiority index of cultivar performance, coefficient of regression, Rank-Sum (sum of ranks of yield and stability variance) and TOP (number of environments at which the cultivar occurred in the top third of the ranks) defined the dynamic stability. In this MET, the genotype PI-537598 was identified as the genotype with the highest yield and high stability of yield.