Phytotron ecology of mutant genes

This study deals with the intralocus mutant hybrid ert‐o 16 X mat‐a 8 (erectoides 16 X Mari). Eleven traits of generative, somigenerative and vegetative character were examined with regard to genotype performance in varied photo‐ and thermoperiods. A system of six photo‐periods with a constant thermoperiod of 15–10°C was worked out. In addition, at the photo‐periods of 16 and 12 hours also the thermoperiods of 20–15° and 20–10°C were applied. The mutants and their F 1 hybrid were found to be highly fertile under all tested conditions, with a certain decrease of fertility in erectoides 16 at high temperature and 8 hours light. This high fertility contrasts with the behaviour of the parental varieties and the mutant‐variety crosses under suboptimal conditions. Heterosis occurred in all photoperiods except 24 hours, especially in the generative traits of dry weight of ripe spikes and kernel number. Generative efficiency, i.e. the ratio of generative to vegetative production, was found generally to be conspicuous in the mutants and their intralocus hybrid, but low at high temperatures and short photoperiods in the case of mutant‐variety crosses and original varieties. In agreement with previous studies heterosis is divided into three types: (1) the somatic (or vegetative) type, (2) the reproductive (or generative) type and (3) the adaptive (or competitive) type. Examples are presented of all three types of heterosis.