The evaluation of genotype x environment interactions of citrus leaf morphology using image analysis and elliptic Fourier descriptors

Variations of leaf form, i.e., differences in shape and size, among citrus varieties and the genotype x environment (GE) interactions influencing the variations were examined. Leaf shape was quantitatively measured by the score of the principal components of elliptic Fourier descriptors (EFDs). Leaf size was measured in terms of area and perimeter. The first four principal components of EFDs, which could explain over 90% of the shape variations, were good measures of the length to width ratio, the position of the center of gravity, the curvature, and the degree of roundness. Nested ANOVA for the leaf form variations in nine citrus varieties indicated that the variations accounted for by the 1st, 2nd and 4th components were inherited. GE interaction of the leaf form was investigated using the data appertaining to seven genotypes from eight locations; the interaction was significant for all the principal components examined except the third. Although the interaction fitted very poorly to a joint linear regression analysis model developed from the data, it was effectively explained by an additive main effect and multiplicative interaction model where the score of the interaction principal component was highly correlated with the stability indices. Our results suggest that the genotype was the main source of variation in leaf shape, but not in size, and that the contribution of GE interaction was minor to both shape and size, although statistically significant at the 1% probability level.