Germination of Immature Soybean Seeds to Shorten Reproductive Cycle Duration

Abstract

The soybean [Glycine max (L.) Merrill] reproductive cycle represents more 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 populations more rapidly. The importance of a pod pretreatment before embryo extraction, the effects of embryo age on germination rate, embryo position in the pod, and the composition of the germination medium (supplemented with sucrose or not) were analyzed to define an optimal technique. Plant recovery rate and genotype effects on germination were evaluated with 22 genotypes representing a broad genetic background. It was necessary to pretreat immature seed by exposing pods to 26°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 development (approximately 18 d after flowering). For three‐seeded pods, the central embryos generally had a higher germination rate than distal and proximal embryos (25 and 44 percentage points, respectively). Whatever the embryo position in the pod, adding sucrose significantly increased the germination of embryos sampled 14 to 18 d after flowering. Plantlets were obtained from 73% of the germinated embryos and the length of cycle was reduced from 130 to 140 d to 65 to 70 d. Average germination of the 22 genotypes was 80%; thus, this technique, paired with the single seed descent method, provides soybean breeders with a tool to develop lines quickly.