Identifying drought-resilient flax genotypes and related-candidate genes based on stress indices, root traits and selective sweep

Abstract

Drought hampers flax yield and oil quality particularly at the reproductive stage. Here, 105 flax accessions were assessed for drought tolerance under irrigated and drought-stressed conditions across three environments using eight stress indices. Total root length (TRL), total root volume (TRV) and diameter class length (DCL) were analyzed in two selected groups of accessions contrasting for drought tolerance. These genotypes were further submitted to selective sweep analysis using 394 genome-wide microsatellite (SSR) loci to identify markers potentially associated with drought tolerance and drought-responsive candidate genes. The results obtained for yield under stress (Ys) and yield under irrigated condition (Yp) indicated significant genotypic response to water treatments (P < 0.001). Hierarchical clustering and heatmap analyses of stress indices identified the oil type flax cultivars O_CAN_C_CN19004 (AC Emerson) and O_CAN_C_CN19003 (AC McDuff) as the most drought tolerant. Some fiber type flax accessions were also clustered in the tolerant group. The drought tolerant group showed 29, 42, and 22% superior TRL, TRV and DCL, respectively, than its sensitive counterpart under drought. The SSR loci under selective sweep, Lu254 and Lu709 were significantly associated with Ys, and accessions carrying the favorable haplotype exhibited 21.7% higher Ys. Various candidate genes involved in absicic acid pathway, auxin signaling, Ca2+ signaling, photosynthesis regulation, and drought-responsive transcription factors were identified at the selective sweep loci. The identified tolerant accessions can be used for conferring drought tolerance to elite cultivars, while the selective sweep SSR loci linked to drought-responsive candidate genes could be useful in MAS.