Genome-Wide Association Mapping of Anther Extrusion in Hexaploid Spring Wheat.

Quddoos H Muqaddasi,Manuela Nagel,Andreas Börner,Klaus Pillen,Ulrike Lohwasser,Marion S Röder,Aimin Zhang

doi:10.1371/journal.pone.0155494

Abstract

In a number of crop species hybrids are able to outperform line varieties. The anthers of the autogamous bread wheat plant are normally extruded post anthesis, a trait which is unfavourable for the production of F1 hybrid grain. Higher anther extrusion (AE) promotes cross fertilization for more efficient hybrid seed production. Therefore, this study aimed at the genetic dissection of AE by genome wide association studies (GWAS) and determination of the main effect QTL. We applied GWAS approach to identify DArT markers potentially linked to AE to unfold its genetic basis in a panel of spring wheat accessions. Phenotypic data were collected for three years and best linear unbiased estimate (BLUE) values were calculated across all years. The extent of the AE correlation between growing years and BLUE values ranged from r = +0.56 (2013 vs 2015) to 0.91 (2014 vs BLUE values). The broad sense heritability was 0.84 across all years. Six accessions displayed stable AE >80% across all the years. Genotyping data included 2,575 DArT markers (with minimum of 0.05 minor allele frequency applied). AE was influenced both by genotype and by the growing environment. In all, 131 significant marker trait associations (MTAs) (|log10 (P)| >FDR) were established for AE. AE behaved as a quantitative trait, with five consistently significant markers (significant across at least two years with a significant BLUE value) contributing a minor to modest proportion (4.29% to 8.61%) of the phenotypic variance and affecting the trait either positively or negatively. For this reason, there is potential for breeding for improved AE by gene pyramiding. The consistently significant markers linked to AE could be helpful for marker assisted selection to transfer AE to high yielding varieties allowing to promote the exploitation of hybrid-heterosis in the key crop wheat.

Highlights

Thanks to the phenomenon of heterosis, F1 hybrid cultivars in a number of crop species are able to out-perform line varieties, both with respect to economic yield and to yield stability [1,2,3,4,5]
The consistently significant markers linked to anther extrusion (AE) could be helpful for marker assisted selection to transfer AE to high yielding varieties allowing to promote the exploitation of hybrid-heterosis in the key crop wheat
The years 2013, 2014 and best linear unbiased estimate (BLUE) values were close to a normal distribution, some skewing was observed in the year 2015 which may be due to environmental conditions (S1 Fig)

Summary

Introduction

Thanks to the phenomenon of heterosis, F1 hybrid cultivars in a number of crop species are able to out-perform line varieties, both with respect to economic yield and to yield stability [1,2,3,4,5]. Attempts to exploit hybridity for bread wheat improvement date back many years [6,7], still the market share of hybrid cultivars remains very small [2]. Significance of Anther Extrusion in Hybrid Wheat Breeding practical difficulties associated with the production of hybrid grain, which arise from the strongly cleistogamous nature of wheat's breeding system [4]. To obtain a reasonable yield of hybrid wheat grain, the female parent needs to be not just male sterile, but its flowers must open sufficiently while the stigma is still receptive in order to allow access for incoming pollen; the male parent, rather than shedding its pollen within the closed floret, must extrude its anthers prior to anthesis. Male sterility can be effectively induced either via treatment with a gametocide or by genetic means [4], some remodelling of floral architecture is required to ensure a sufficient volume of viable pollen [7,8]

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