Mapping Freezing Tolerance QTL in Alfalfa Based on Indoor Phenotyping

Abstract

Abstract Background Winter freezing temperature impacts alfalfa (Medicago sativa L.) persistence and seasonal yield and can lead to the death of the plant. Understanding the genetic mechanisms of alfalfa freezing tolerance (FT) using high-throughput phenotyping and genotyping is crucial to select suitable germplasm and develop winter-hardy cultivars. Several clones of an alfalfa F1 mapping population (3010 x CW 1010) were phenotyped for FT using a cold chamber. The population was genotyped with SNP markers identified using genotyping by sequencing (GBS) and the QTL associated with FT were mapped on the parent-specific linkage maps. The ultimate goal is to develop non-dormant and winter-hardy alfalfa cultivars that can produce extended growth in the areas where winters are often mild. Results Alfalfa FT screening method optimized in this experiment comprises three major steps; clone preparation, acclimation, and freezing test. Twenty clones of each genotype were tested, where 10 samples were treated with freezing temperature, and 10 were used as controls. A moderate positive correlation (r ~ 0.36, P < 0.01) was observed between indoor FT and field-based winter hardiness (WH), suggesting that the indoor FT test is useful as an indirect selection method for winter hardiness of alfalfa germplasm. We detected a total of 20 QTL for four traits; visual rating-based FT, percentage survival (PS), treated to control regrowth ratio (RR), and treated to control biomass ratio (BR). Some QTL overlapped with WH QTL reported previously, suggesting a genetic relationship between FT and WH. Some favorable QTL from the winter-hardy parent (3010) potentially represented the genic region of a cold tolerance gene, the c-repeat binding factor (CBF). These QTL were located on the terminal end of chromosome 6 which is considered a location of the CBF homologs in alfalfa.Conclusions The indoor freezing tolerance selection method reported here is valuable for alfalfa breeders to accelerate breeding cycles through indirect selection. The QTL and associated markers add to the genomic resources needed by the alfalfa research community and can be used in marker-assisted selection (MAS) for alfalfa cold tolerance improvement.

Plant phenotyping relevance

アルファルファの凍結耐性を測定する室内スクリーニング法を最適化し、圃場の冬季耐寒性との相関で有用性を検証しているため、植物表現型取得法が研究の中心である。

Code and data availability

The preprint reports indoor freezing-tolerance phenotyping and QTL mapping in alfalfa, but no public phenotype dataset, images, analysis code, or trained models are disclosed. The only public deposit is the GBS raw reads in NCBI SRA (SRP150116), which is a molecular omics deposit, not a phenotyping asset. The only data

No evidence-backed public reproduction asset is currently recorded.