Distribution and Nucleotide Diversity of Yr15 in Wild Emmer Populations and Chinese Wheat Germplasm.

Yu He,Lianquan Zhang,Yun Jiang,Dengcai Liu,Guoyue Chen,Jirui Wang,Lin Huang,Bihua Wu,Lihua Feng,Tzion Fahima,Jun Yan,Gang Zhao

doi:10.3390/pathogens9030212

Yu He, Lianquan Zhang + Show 10 more

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https://doi.org/10.3390/pathogens9030212

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Abstract

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a devastating fungal disease of wheat. The wild emmer gene, Yr15 (Wtk1), which confers a strong broad-spectrum resistance to Pst isolates, is composed of kinase and pseudokinase domains. The analysis of 361 wild emmer accessions from a wide range of natural habitats confirms that functional Wtk1 is distributed mainly along a narrow axis from Mt. Carmel to Mt. Hermon regions, in the northern part of Israel, where environmental conditions are favorable to the onset of stripe rust. An analysis of full-length Wtk1 DNA sequences from 49 wild emmer accessions identified three haplotypes and extremely low nucleotide diversity (π = 0.00002). The sequence diversity of Wtk1 is 9.5 times lower than that of broad-spectrum partial resistance gene Yr36 (π = 0.00019), and both are in sharp contrast to the high level of nucleotide diversity previously reported for race-specific resistance genes (e.g., Lr10 and Pm3). However, the nonfunctional wtk1 sequences possess high level of nucleotide diversity (π = 0.07). These results may reflect the different resistance mechanisms and the different evolutionary processes that shaped these resistance genes. Yr15 was absent in 189 Chinese wheat landraces and was present in only 1.02% of the 583 tested modern Chinese wheat cultivars. These results corroborate our previous results showing that Yr15 was absent in 94% of a worldwide collection of 513 wheat cultivars, therefore indicating the importance of Yr15 in wheat stripe rust resistance breeding programs in China and elsewhere around the globe.

Highlights

Wheat provides about 20% of the calories and proteins in the human diet globally [1]
all-stage resistance (ASR) is effective at both seedling and adult plant growth stages, whereas adult plant resistance (APR) is primarily effective in later stages of plant growth [3]
ASR is usually controlled by a single resistance gene conferring high levels of resistance to specific Puccinia striiformis f. sp. tritici (Pst) races [4]

Summary

Introduction

Wheat provides about 20% of the calories and proteins in the human diet globally [1]. Tritici (Pst), the causal agent of wheat stripe rust, is one of the most devastating. Planting wheat cultivars with adequate levels of resistance is the most effective and environmentally friendly strategy to control stripe rust. Based on plant growth stages, stripe rust resistance can be classified as either all-stage resistance (ASR) or adult plant resistance (APR). ASR is usually controlled by a single resistance gene conferring high levels of resistance to specific Pst races [4]. This kind of resistance is vulnerable and can be rapidly overcome by new virulent races that frequently evolve in the Pst populations [5–7]. APR is usually quantitatively inherited and often shows a broad-spectrum resistance that is partial and, in some cases, has proven to be more durable than ASR [8,9]

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