Modified speed breeding approach reduced breeding cycle to less than half in vegetable soybean [Glycine max (L.) Merr.]

Abstract

Vegetable soybean [Glycine max (L.) Merr.] is gaining popularity because of its high nutritive values and health benefits; however, its productivity is scarce. Recognizing the need to accelerate breeding progress, a modified approach of ‘speed breeding’ was used in 16 vegetable soybean genotypes to reduce the breeding periods. The genotypes were exposed to cycles of 10 h light (30 °C) and 14 h dark (25 °C) with CO₂ (550 ppm) and without CO₂ supplementation under the light intensity of 220 µmol m⁻² s⁻¹ at the canopy level and 70–80% relative humidity. To reduce the time further, physiologically matured pods were harvested once they changed their color from green to greenish yellow and dried in the oven for 7 days at 25 ± 2 °C with RH 10–20%. The genotypes showed variable responses towards days to flowering coupled with an increase in the number of pods, number of seeds and seed weight per plant, and 100 seed weight during a short breeding period under CO₂ supplement. A couple of genotypes behaved indifferently under normal and elevated CO₂ levels. The fresh oven-dried seeds displayed 73.33–100% germination, while that in the seeds stored at 4 °C for 10 months was 80–100%. Thus, the modified speed breeding technique could effectively reduce the breeding period without affecting the germination of the seeds. With this approach, we could save 6–34 days in a genotype dependent way which would at least give 4–4.5 generations of soybean per year instead of the usual 1–2 generations. Further, the reduction in maturity duration was more in longer duration genotypes than the shorter duration ones. This represents the country’s initial report of rapid breeding in vegetable soybean and offers ample opportunity for rapid generation advancement in this crop.