Use of the phytotron in mutation breeding

Many X-ray induced Pisum mutants and recombinants were studied under long and short day phytotron conditions with different thermoperiods. The flowering behaviour and shoot structure were investigated as functions of the environmental factors offered and the genotypic constitution of the material tested. Regarding heat tolerance, a broad, genetically conditioned variability was found in the material studied. Genotypes were selected that tolerated day temperatures of up to 35 deg. C under short day conditions (12/12 h) if cool night temperatures for recovery were provided. The gene efr (=lfa) of the Pisum genome showed great susceptibility to different photoperiods and to the presence of other distinct mutant genes in the genome. It can cause pronounced earliness under long and short day conditions; earliness under long day and lateness under short day conditions; and lateness under long day and non-flowering under short day conditions. Many efr recombinants were selected that showed a favourable flowering under 12/12 h short day conditions. Our high yielding fasciated mutants do not flower under short day conditions. A large number of fasciated recombinants were selected that flowered under both long and short day conditions. It should be possible to use the ''stem fasciation'' (= high seed production) trait of Pisum in countries with short day climates. (author). 12 refs, 4 figs