Abstract
In alkaline soils in arid and semi-arid areas toxic concentrations of the micronutrient boron (B) are problematic for many cereal and legume crops. Molecular markers have been developed for B toxicity in cereals and Medicago. There is a need for such tools in clovers—Trifolium. To this end, we undertook a genome-wide association study (GWAS) with a diversity panel of subterranean clover (Trifolium subterraneum L.), an established model pasture legume for genetic and genomic analyses for the genus. The panel comprised 124 T. subterraneum genotypes (97 core collection accessions and 27 Australian cultivars). Substantial and useful diversity in B toxicity tolerance was found in T. subterraneum. Such variation was continuously distributed and exhibited a high broad sense heritability H 2 = 0.92. Among the subspecies of T. subterraneum, ssp. brachycalycinum was most susceptible to B toxicity (P < 0.05). From the GWAS, the most important discoveries were single-nucleotide polymorphisms (SNPs) located on Chr 1, 2, and 3, which mapped to haplotype blocks providing potential genes for a B toxicity tolerance assay and meriting further investigation. A SNP identified on Chr 1 aligned with Medicago truncatula respiratory burst oxidase-like protein (TSub_ g2235). This protein is known to respond to abiotic and biotic stimuli. The identification of these novel potential genes and their use to design markers for marker-assisted selection offer a pathway in pasture legumes to manage B toxicity by exploiting B tolerance.
Highlights
Boron (B) is one of the essential micronutrients for healthy plant growth (Tomić et al, 2015) and is available to plants as boric acid (Reid, 2014)
Selection of the core collection followed the methodology of Ghamkhar et al (2008) to identify a subset of 760 lines, on the basis of 1) diversity for eco-geographical data from their sites of collection; and 2) agromorphological data obtained by the Australian Trifolium Genetic Resource Centre (ATGRC) of the Department of Agriculture and Food Western Australia (DAFWA)
To establish a suitable screening system and to determine the best concentration of B for phenotypic traits in a hydroponic system, ten genotypes of T. subterraneum were tested under four different concentrations of B
Summary
Boron (B) is one of the essential micronutrients for healthy plant growth (Tomić et al, 2015) and is available to plants as boric acid (Reid, 2014). Due to its small molecular size and high membrane permeability in comparison to many other nutrients, the uptake and diffusion of B can be difficult for plants to control (Reid, 2014). B deficiency is relatively easy to manage using B-rich fertilizers, B toxicity is more difficult to manage. Soil B concentration can be reduced by leaching, and B availability can be modified by pH adjustment, but this is impractical on a large scale (Yau and Ryan, 2008). The use of genetic variation and plant breeding for tolerance is likely the best way to overcome toxicity (Yau and Ryan, 2008)
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