Abstract
Hybrid wheat breeding is gaining prominence worldwide because it ensures higher and more static yield than conventionally bred varieties. The cleistogamous floral architecture of wheat (Triticum aestivum L.) impedes anthers inside the floret, making it largely an inbreeder. For hybrid seed production, high anther extrusion is needed to promote cross pollination and to ensure a high level of pollen availability for the seed plant. This study, therefore, aimed at the genetic dissection of anther extrusion (AE) in panels of spring (SP), and winter wheat (WP) accessions by genome wide association studies (GWAS). We performed GWAS to identify the SNP markers potentially linked with AE in each panel separately. Phenotypic data were collected for 3 years for each panel. The average levels of Pearson's correlation (r) among all years and their best linear unbiased estimates (BLUEs) within both panels were high (r(SP) = 0.75, P < 0.0001;r(WP) = 0.72, P < 0.0001). Genotypic data (with minimum of 0.05 minor allele frequency applied) included 12,066 and 12,191 SNP markers for SP and WP, respectively. Both genotypes and environment influenced the magnitude of AE. In total, 23 significant (|log10(P)| > 3.0) marker trait associations (MTAs) were detected (SP = 11; WP = 12). Anther extrusion behaved as a complex trait with significant markers having either favorable or unfavorable additive effects and imparting minor to moderate levels of phenotypic variance (R2 (SP) = 9.75−14.24%; R2 (WP) = 9.44−16.98%). All mapped significant markers as well as the markers within their significant linkage disequilibrium (r2 ≥ 0.30) regions were blasted against wheat genome assembly (IWGSC1+popseq) to find the corresponding genes and their high confidence descriptions were retrieved. These genes and their orthologs in Hordeum vulgare, Brachypodium distachyon, Oryza sativa, and Sorghum bicolor revealed syntenic genomic regions potentially involved in flowering-related traits. Moreover, the expression data of these genes suggested potential candidates for AE. Our results suggest that the use of significant markers can help to introduce AE in high yielding varieties to increase cross fertilization rates and improve hybrid-seed production in wheat.
Highlights
In many crops, hybrids have almost completely replaced the conventionally bred varieties because of their potential of higher and more stable yields even in marginal environments (Schnable and Springer, 2013)
Anther retention (AR; number of non-extruded anthers) was scored on field in both panels 5–10 days post-anthesis for the years 2013, 2014, and 2015 by observing the anthers retained inside the four pairs of primary and secondary florets sampled from the central portion of four spikes per plot
The laboratory-based method was preferred for the subsequent genetic analysis, because it avoided difficulties related with the on field Anther extrusion (AE) scoring and lodging of the non-dwarf accessions and because it allowed the processing of large numbers of accessions
Summary
Hybrids have almost completely replaced the conventionally bred varieties because of their potential of higher and more stable yields even in marginal environments (Schnable and Springer, 2013). Hybrid wheat breeding has a long history, still the wheat hybrid market is very small This slow progress in hybrid wheat seed production is due to the hermaphroditic cleistogamous architecture of wheat florets which impedes proper anther extrusion to allow sufficient pollen shedding outside the floret. To guarantee a sound hybrid wheat seed production program, the cleistogamous nature of wheat needs an alteration to open flowering (Whitford et al, 2013). This floral modification will allow anthers to extrude during anthesis for sufficient pollen shedding outside the florets, so they may become available for the female lines via wind pollination. The existing insignificant cross fertilization rates in wheat can be increased by ensuring a higher level of anther extrusion for appropriate pollen shedding outside of florets
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