GERMINATION OF IMMATURE SOYBEAN SEEDS TO SHORTEN REPRODUCTIVE-CYCLE DURATION

The soybean [Glycine max (L.) Merrill] reproductive cycle represents m ore than 50% of the length of the total growth cycle. Immature embryo culture could be used to shorten this cycle. This study was conducted to develop an efficient technique to shorten the soybean reproductive cycle and to make it possible to develop recombinant lines from popula tions more rapidly. The importance of a pod pretreatment before embryo extraction, the effects of embryo age on germination rate, embryo pos ition in the pod, and the composition of the germination medium (suppl emented with sucrose or not) were analyzed to define an optimal techni que. Plant recovery rate and genotype effects on germination were eval uated with 22 genotypes representing a broad genetic background. It wa s necessary to pretreat immature seed by exposing pods to 26 degrees C for 4 d to induce germination. Best results (up to 100% germination) were obtained from embryos sampled at the end of lag phase of seed dev elopment (approximately 18 d after flowering). For three-seeded pods, the central embryos generally had a higher germination rate than dista l and proximal embryos (25 and 44 percentage points, respectively). Wh atever the embryo position in the pod, adding sucrose significantly in creased the germination of embryos sampled 14 to 18 d after flowering. Plantlets were obtained from 73% of the germinated embryos and the le ngth of cycle was reduced from 130 to 140 d to 65 to 70 d. Average ger mination of the 22 genotypes was 80%; thus, this technique, paired wit h the single seed descent method, provides soybean breeders with a too l to develop lines quickly.