Rapid generation advancement (RGA): enabling speed breeding in chickpea, and lentil

Simple, and cost-effective, and easy to implement rapid generation advancement (RGA) protocols are standardized by the GLDC crop breeding teams at ICRISAT and ICARDA in chickpea and lentil to enhance the rate of genetic gain by reducing the breeding cycle time.

In chickpea, with the new RGA protocol developed at ICRISAT, the chickpea breeding team can now produce 6 to 7 generations per year under semi-controlled greenhouse conditions, by extending the photoperiod (light) during the seedling stage resulting in early flower induction within 20-25 days after sowing (DAS), as against the normal flowering at 40 to 50 DAS. Immature seeds were also germinated to further reduce the mean number of generations produced per year to 7, 6.2, and 6 in early, medium, and late-maturing genotypes, respectively. The protocol was standardized using six chickpea varieties belonging to different maturity groups.

In lentil, rapid generation cycling will allow 4-5 generations per year through single seed descent (SSD) instead of only one or two generations in conventional greenhouse-based methods (center level) reducing field cost, labor cost, and time. Two lentil genotypes (ILL590 and ILL759) were grown in a growth chamber and greenhouse at a high density of supplemental lighting (using far-red enriched LED and blue LED lights) under an extended photoperiod of 22 h light/25.5 °C and 2 h dark/15 °C. Five plants of each genotype were grown in a growth room and glasshouses at 25 ⁰C. The seeds were sown in plastic pots (0.5 L) filled with a soil mix (1:1 peat moss and soil). The results indicated that the first flower was at 23 to 26  DAS, while 31 to 34 DAS for the first pod, and pods at physiological maturity were observed 51 to 55 DAS in ILL 590 and ILL 759, respectively.

The researchers of chickpea and lentil breeding programs in Africa and Asia are the immediate beneficiaries of this RGA protocol/technology as the crop breeding programs of CG and NARS can increase resource-use efficiency, and enhance the rate of the genetic gain with the use of these new protocols. These protocols are simple, and cost-efficient with the following significant benefits.

Enhanced rate of genetic gain: Generation cycle (L) is the single parameter in the denominator of the breeder’s equation for estimating genetic gain (ΔG = (σa)(i)(r)/L). This exponential increase in genetic gain would be possible by manipulating the time factor compared to other factors such as additive variance (σa), selection intensity (i), and selection accuracy (r) in the genetic gains equation.

Cost reduction in breeding programs: The RGA technology will allow us to follow single seed descent (SSD) method of generation advancement which is much easier and effective compared to pedigree/bulk breeding methods that involve selection at every generation and maintenance of pedigree records. While field operations are always under high risk of local weather conditions, it is eliminated while advancing generations under greenhouse conditions, minimizing the failure of reaching the target. 

Time saved: The single-seed descent (SSD) method of RGA uses a single seed and less space and time (less than two months to complete a cycle) for generation advancement. 

Easy adoption by the scientific community: Selection in early generations is laborious and runs the risk of losing valuable genotypes due to unfavorable linkages. RGA does not have that problem as the selection is not practiced until the F5-6 generations. The researchers equipped with greenhouse facilities can undertake the RGA protocol to advance the breeding populations using existing infrastructure on a small scale. The ICRISAT and ICARDA are disseminating the technology to the researcher under various bilateral projects. 

The shortened breeding cycle methods will be deployed and piloted for implementation based on priority and breeding needs at the regional hubs. Integrating RapidGen with crop breeding offers tremendous opportunities to overcome the limitations of seasons and photoperiods when grown under field conditions. Breeding tools such as marker-assisted selection (MAS), and genomic selection (GS) can be easily integrated with RGA technology towards modernization of breeding programs for achieving higher genetic gains in respective crops.