Abstract
Phytophthora root rot (PRR) causes serious annual soybean yield losses worldwide. The most effective method to prevent PRR involves growing cultivars that possess genes conferring resistance to Phytophthora sojae (Rps). In this study, QTL-sequencing combined with genetic mapping was used to identify RpsX in soybean cultivar Xiu94-11 resistance to all P. sojae isolates tested, exhibiting broad-spectrum PRR resistance. Subsequent analysis revealed RpsX was located in the 242-kb genomic region spanning the RpsQ locus. However, a phylogenetic investigation indicated Xiu94-11 carrying RpsX is distantly related to the cultivars containing RpsQ, implying RpsX and RpsQ have different origins. An examination of candidate genes revealed RpsX and RpsQ share common nonsynonymous SNP and a 144-bp insertion in the Glyma.03g027200 sequence encoding a leucine-rich repeat (LRR) region. Glyma.03g027200 was considered to be the likely candidate gene of RpsQ and RpsX. Sequence analyses confirmed that the 144-bp insertion caused by an unequal exchange resulted in two additional LRR-encoding fragments in the candidate gene. A marker developed based on the 144-bp insertion was used to analyze the genetic population and germplasm, and proved to be useful for identifying the RpsX and RpsQ alleles. This study implies that the number of LRR units in the LRR domain may be important for PRR resistance in soybean.
Highlights
Soybean [Glycine max (L.) Merr] is one of the most important economic crops, accounting for more than half of the global oilseed production [1]
The resistance to 14 P. sojae isolates with varying virulence levels was assessed for the Phytophthora root rot (PRR)-resistant Xiu94-11 and 22 other cultivars each containing a different identified resistance to Phytophthora sojae (Rps) gene as well as four PRR-susceptible cultivars (Zhonghuang13, Williams, Zhonghuang47, and Jikedou2) as controls
Unlike the Rps genes in tandemly arranged NBS-leucine-rich repeat (LRR) gene clusters, resistant genotypes Xiu94-11 (RpsX) was mapped to an interval on the short arm of chromosome 3 lacking NBS-LRR genes
Summary
Soybean [Glycine max (L.) Merr] is one of the most important economic crops, accounting for more than half of the global oilseed production [1]. Sustainable soybean cultivation is largely limited by diseases caused by diverse pathogens, including the soil-borne oomycete Phytophthora sojae, which causes Phytophthora root rot (PRR), with annual economic losses of 1–2 billion worldwide [2,3,4,5,6]. In China, PRR was first detected in Heilongjiang province in 1989, and it has since spread to most soybean-producing areas [7]. This disease can occur at any soybean plant developmental stage. Compared with the application of biological and chemical agents, growing PRR-resistant cultivars is a more environmentally friendly method for the sustainable development and production of crops
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