GENOTYPE X ENVIRONMENT INTERACTION IN QTL ANALYSIS OF AN INTERVARIETAL ALMOND CROSS BY MEANS OF GENETIC-MARKERS

Besides QTL location and the estimation of gene effects, QTL analysis based on genetic markers could be used to comprehensively investigate quantitative trait-related phenomena such as pleiotropy, gene interact ions, heterosis, and genotype-by-environment interaction (G x E). Give n that the G x E interaction is of great relevance in tree improvement , the objective of the research presented here was to study the effect of years on QTL detection for 15 quantitative traits by means of isoz ymatic markers in a large progeny group of an intervarietal cross of a lmond. At least 17 putative QTLs were detected, 3 of which had alleles with opposite effects to those predicted from the parental genotypes. Only 3 QTLs behaved homogeneously over the years. Three possible caus es are discussed in relation to this lack of stability: the power of t he test statistic being used, the low contribution of the QTL to the g enetic variation of the trait, and a differential gene expression depe ndent on the year (G x E). Most cases showing lack of stability involv ed traits whose heritability estimates change drastically from year to year and/or whose correlation coefficients between years are low, sug gesting the presence of G x E as the most likely cause. A marker-assis ted selection scheme to improve late flowering and short flowering dur ation is suggested for an early and wide screening of the progeny.