Genotype-environment interaction for awn development in isogenic lines of barley.

Awn length of four isogenic lines of barley differing by two genes for awn development (A andB) and their short iinkage blocks was evaluated at a wide range of plant densities (0.002 to 3.345 m(2)/plant) for two years. Awn development was reduced at high plant density. The quarter-awned genotype (aaBB) became phenotypically awnless (aabb) at high plant density. Similar results were obtained each year and the genotype x plant density effect was the major portion of the genotype-environment interaction variance. Additive (α A , α B ) and additive x additive (α AB ) gene effects were computed for each plant density for lateral and central floret awn length. For lateral awns α AB was not affected, but α A and α B increased with decreased plant density. In contrast, for central awns α A and α AB decreased and α B increased with decreased plant density.Central floret awns measured at each spike node showed that high plant density reduced awn development most in the lower half of the spike. This is the zone of most rapid awn differentiation and since culm elongation and spike growth rates were greatly increased by high plant density, it was suggested that rapid growth invoked a stress on awn development and differentially altered the expression ofA andB.