Strategies for accelerating genetic gains in crop plants: special focus on speed breeding

Abstract

Feeding 10 billion people sustainably by 2050 in the era of slow genetic progress has spurred urgent calls to bring more crops per unit time. Over the last century, crop physiologists and breeders have been trying to alter plant biology to investigate and intervene in developmental processes under controlled chambers. Accelerating the breeding cycle via "speed breeding" was the outcome of these experiments. Speed breeding accelerates the genetic gain via phenome and genome-assisted trait introgression, re-domestication, and plant variety registration. Furthermore, early varietal release through speed breeding offers incremental benefits over conventional methods. However, a lack of resources and species-specific protocols encumber the technological implementation, which can be alleviated by reallocating funds to establish speed breeding units. This review discusses the limitations of conventional breeding methods and various alternative strategies to accelerate the breeding process. It also discusses the intervention at various developmental stages to reduce the generation time and global impacts of speed breeding protocols developed so far. Low-cost, field-based speed breeding protocol developed by Punjab Agricultural University, Ludhiana, Punjab, India to harvest at least three generations of wheat in a year without demanding the expensive greenhouses or growth chambers is also discussed.

Keywords: And economic assessment; Conventional breeding; Doubled haploid; Field-based speed breeding; In-vitro nursery; Rapid generation advancement.

Fig. 1

Various strategies to speed up the breeding process: (a) rapid generation advancement with single seed descent (RGA-SSD) method; (b) shuttle breeding to harvest two generations in a year; (c) double haploid (DH) production through chromosome elimination (Bulbosum technique and wheat × maize system), gametophytic cell (anther, pollen, and ovary) culture, and genetic engineering (cenh3); (d) biotron breeding system (BBS) for generation advancement in rice; (e) in-vitro nurseries to induce meiosis and mitosis to accelerate the generation advancement; (f) comparison of generation advancement using speed breeding, greenhouse, and conventional (field) breeding methods in wheat, chickpea, and brassica

Fig. 2

Step-wise evolution of speed breeding technology and its integration with high-throughput phenotyping, high-throughput, genomic selection, and genome editing tools

Fig. 3

Intervening the key developmental stages of plants to reduce generation time

Fig. 4

Time scale of varietal development and the annual benefits achieved through conventional breeding, shuttle breeding, double haploid (DH) or rapid generation advancement (RGA), speed breeding, speed breeding with genomic selection (SpeedGS), and SpeedGS with SpeedDUS (speed breeding with varietal registration)

Fig. 5

Incremental benefits of accelerated breeding methods over conventional breeding approach at 1% (yellow), 5% (orange), and 10% (blue) discount rates

Fig. 6

Field-based, low-cost, speed breeding protocol developed by PAU, Ludhiana for generation advancement in wheat