Speed breeding: a powerful tool to accelerate crop research and breeding

Abstract

The growing human population and a changing environment have raised significant concern for global food security, with the current improvement rate of several important crops inadequate to meet future demand [1]. This slow improvement rate is attributed partly to the long generation times of crop plants. Here we present a method called 'speed breeding', . CC-BY 4.0 International license It is made available under a (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/161182 doi: bioRxiv preprint first posted online Jul. 9, 2017; Watson and Ghosh et al. (2017) 2 which greatly shortens generation time and accelerates breeding and research programs.Speed breeding can be used to achieve up to 6 generations per year for spring wheat (Triticum aestivum), durum wheat (T. durum), barley (Hordeum vulgare), chickpea (Cicer arietinum), and pea (Pisum sativum) and 4 generations for canola (Brassica napus), instead of 2-3 under normal glasshouse conditions. We demonstrate that speed breeding in fully-enclosed controlled-environment growth chambers can accelerate plant development for research purposes, including phenotyping of adult plant traits, mutant studies, and transformation.The use of supplemental lighting in a glasshouse environment allows rapid generation cycling through single seed descent and potential for adaptation to larger-scale crop improvement programs. Cost-saving through LED supplemental lighting is also outlined. We envisage great potential for integrating speed breeding with other modern crop breeding technologies, including high-throughput genotyping, genome editing, and genomic selection, accelerating the rate of crop improvement.For most crop plants, the breeding of new, advanced cultivars, takes several years. Following crossing of selected parent lines, 4-6 generations of inbreeding are typically required to develop genetically stable lines for evaluation of agronomic traits and yield. This is particularly timeconsuming for field-grown crops that are often limited to only 1-2 generations per year. Here, we present flexible protocols for "speed breeding" that use prolonged photoperiods to accelerate the developmental rate of plants [2], thereby reducing generation time. We highlight the opportunity presented by speed breeding and detail protocols to inspire widespread adoption as a state-of-theart breeding and research tool.To evaluate speed breeding as a method to accelerate applied and basic research on cereal species, standard genotypes of spring bread wheat (T. aestivum), durum wheat (T. durum), barley (H. vulgare) and the model grass Brachypodium distachyon were grown in a controlled environment room with extended photoperiod (22 hours light/2 hours dark) ( Fig. 1; Methods:Speed breeding I; Supplementary Table 1). A light/dark period was chosen over a continuous photoperiod to support functional expression of circadian clock genes [3]. Growth was compare...

Speed breeding in growth chambers and glasshouses for crop breeding and model plant research

“…The generation time of most plant species represents a 33 bottleneck in applied research programs and breeding, creating the need for technologies that 34 accelerate plant development and generation turnover. Recently we reported protocols for 'speed in barley, and pod shattering in canola 1 .…”

“…22 °C / 17 °C for 22 hours light and 2 hours dark, respectively, is used at JIC (Speed breeding I) 1 . In…”

A roadmap for gene functional characterisation in wheat

“…Recently, the "speed breeding" technique has been implemented in wheat, which uses extended day lengths of 22 hours and improved light quality to accelerate the generation time in wheat (Watson et al, 2018). Reduction of generation times to 8-10 weeks is achieved through an accelerated growth rate and harvesting of immature seeds 2-3 weeks post anthesis.…”

“…Incorporating speed breeding within crossing programmes can reduce the time required to produce and phenotype double mutants in tetraploid wheat to less than 7.5 months and triple mutants in hexaploid wheat to less than 10 months (Figure 4). In addition to reducing generation times, it has been shown that several traits of interest such as disease resistance, height and flowering time can be properly characterised under speed breeding conditions (Watson et al, 2018).…”

“…An additional limitation had been the generation time of wheat, which ranges from four to six months depending on the requirement of cold periods (vernalisation) to induce flowering. Again, recent advances in growth conditions have radically changed these timeframes (Watson et al, 2018). Wheat has now become a tractable system for translational, comparative and functional genomics and thus attractive for both wheat and non-wheat researchers.…”