Phytotron ecology of mutant genes

Six mutants of Bonus barley, involving loci mat‐a, b and c for increased earliness as well as 6 intralocus and 8 interlocus F 1 combinations, were cultivated in the Stockholm phytotron, two photoperiods (24 and 12 hours) and one thermoperiod (15–10°) being applied. The homozygous mutants and their F 1 hybrids were compared with the original parent variety Bonus in 13 different traits. At a day‐length of 24 hours the mutants and their intralocus hybrids were mostly inferior to Bonus but at 12 hours often strikingly superior. At both photoperiods dihybrid overdominance (heterosis) was common in the interlocus F 1 hybrids. It was pronounced in generative traits, less in semigenerative and vegetative respects. Phenotypic variability was measured by coefficients of variation. In most genotypes variability was higher at 12 than at 24 hours. Some mutant genotypes, however, were more variable at the long than at the short photo‐period. Phenotypic variability is often changed from a state of equilibrium and regularity (an “endotaxy”) at optimal conditions to a state of internal unrest and unbalance under the influence of suboptimal climatic conditions and, finally, to a conspicuous disorder (an “endoataxy”). The change from phenotypical normality to unbalance and monstrosity is determined by genotype‐environment interactions, relating to individual traits.