Abstract
BackgroundAdaptation to drought-prone environments requires robust root architecture. Genotypes with a more vigorous root system have the potential to better adapt to soils with limited moisture content. However, root architecture is complex at both, phenotypic and genetic level. Customized mapping panels in combination with efficient screenings methods can resolve the underlying genetic factors of root traits.ResultsA mapping panel of 233 spring barley genotypes was evaluated for root and shoot architecture traits under non-stress and osmotic stress. A genome-wide association study elucidated 65 involved genomic regions. Among them were 34 root-specific loci, eleven hotspots with associations to up to eight traits and twelve stress-specific loci. A list of candidate genes was established based on educated guess. Selected genes were tested for associated polymorphisms. By this, 14 genes were identified as promising candidates, ten remained suggestive and 15 were rejected. The data support the important role of flowering time genes, including HvPpd-H1, HvCry2, HvCO4 and HvPRR73. Moreover, seven root-related genes, HERK2, HvARF04, HvEXPB1, PIN5, PIN7, PME5 and WOX5 are confirmed as promising candidates. For the QTL with the highest allelic effect for root thickness and plant biomass a homologue of the Arabidopsis Trx-m3 was revealed as the most promising candidate.ConclusionsThis study provides a catalogue of hotspots for seedling growth, root and stress-specific genomic regions along with candidate genes for future potential incorporation in breeding attempts for enhanced yield potential, particularly in drought-prone environments. Root architecture is under polygenic control. The co-localization of well-known major genes for barley development and flowering time with QTL hotspots highlights their importance for seedling growth. Association analysis revealed the involvement of HvPpd-H1 in the development of the root system. The co-localization of root QTL with HERK2, HvARF04, HvEXPB1, PIN5, PIN7, PME5 and WOX5 represents a starting point to explore the roles of these genes in barley. Accordingly, the genes HvHOX2, HsfA2b, HvHAK2, and Dhn9, known to be involved in abiotic stress response, were located within stress-specific QTL regions and await future validation.
Highlights
Adaptation to drought-prone environments requires robust root architecture
Considerable reductions in the coefficient of variation (CV) in the osmotic stress treatment were observed for the four image-based root traits, ranging from 4% (Rth) to 51% (Trv) (Additional file 1: Table S3)
By comparing Quantitative Trait Loci (QTL) positions found in other studies, we found a number of QTL co-locating with shoot biomass QTL [88] detected in a subset of our collection (QTL-3H-5, QTL-4H-7, QTL-7H-1) and with drought and biomass related QTL in a winter barley collection [89] (Additional file 1: Table S8)
Summary
Adaptation to drought-prone environments requires robust root architecture. Improving crop performance and grain yield and stability under drought is a major goal of plant breeding programs targeting these regions. Vigorous root systems are often considered as a primary target to breed for drought tolerance [9,10,11,12,13]. The importance of root traits as indirect selection criteria to increase yield was revealed by recent studies showing a significant positive relationship between root traits at seedling stage and grain yield under drought conditions in barley [14,15,16,17], wheat [18, 19] and in maize [5]
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