Abstract
BackgroundRice sheath blight (ShB) disease, caused by the pathogenic fungus Rhizoctonia solani, causes significant yield losses globally. US weedy rice populations, which are de-domesticated forms of indica and aus cultivated rice, appear to be more resistant to ShB than local japonica cultivated rice. We mapped quantitative trait loci (QTL) associated with ShB resistance using two F8 recombinant inbred line populations generated from crosses of an indica crop variety, Dee-Geo-Woo-Gen (DGWG), with individuals representing the two major US weed biotypes, straw hull (SH) and black hull awned (BHA).ResultsWe identified nine ShB resistance QTL across both mapping populations. Five were attributable to alleles that affect plant height (PH) and heading date (HD), two growth traits that are known to be highly correlated with ShB resistance. By utilizing an approach that treated growth traits as covariates in the mapping model, we were able to infer that the remaining four QTL are involved in ShB resistance. Two of these, qShB1–2 and qShB4, are different from previously identified ShB QTL and represent new candidates for further study.ConclusionOur findings suggest that ShB resistance can be improved through favorable plant growth traits and the combined effects of small to moderate-effect resistance QTL. Additionally, we show that including PH and HD as covariates in QTL mapping models is a powerful way to identify new ShB resistance QTL.
Highlights
Rice sheath blight (ShB) disease, caused by the pathogenic fungus Rhizoctonia solani, causes significant yield losses globally
Weedy rice accessions have not been used in developing ShB-resistant mapping populations despite their potential to harbor unique resistance alleles (Liu et al 2015)
Several factors suggest that these weeds could be promising sources of ShB resistance genes such as: 1) The straw hull (SH) and black hull awned (BHA) strains are among the most predominant weeds in southern US rice fields where sheath-blight is the most destructive pathogen (Wrather and Sweets 2009), which suggests that they may possess a mechanism of disease resistance that confers a competitive advantage
Summary
Rice sheath blight (ShB) disease, caused by the pathogenic fungus Rhizoctonia solani, causes significant yield losses globally. Rice sheath blight (ShB) disease, caused by the soil borne fungus Rhizoctonia solani (teleomorph: Thanatephorus cucumeris), is one of the most devastating pathogens of rice worldwide (Savary et al 2006). Several factors suggest that these weeds could be promising sources of ShB resistance genes such as: 1) The SH and BHA strains are among the most predominant weeds in southern US rice fields where sheath-blight is the most destructive pathogen (Wrather and Sweets 2009), which suggests that they may possess a mechanism of disease resistance that confers a competitive advantage. 2) Weed × crop mapping populations for both biotypes have already been used to identify resistance QTL for another fungal disease (rice blast) (Liu et al 2015). Several factors suggest that these weeds could be promising sources of ShB resistance genes such as: 1) The SH and BHA strains are among the most predominant weeds in southern US rice fields where sheath-blight is the most destructive pathogen (Wrather and Sweets 2009), which suggests that they may possess a mechanism of disease resistance that confers a competitive advantage. 2) Weed × crop mapping populations for both biotypes have already been used to identify resistance QTL for another fungal disease (rice blast) (Liu et al 2015). 3) because the two weed biotypes evolved independently and have historically shown limited hybridization with US cultivated rice (Reagon et al 2010), any resistance alleles that they carry are likely to be unique to the weeds and unlikely to have been previously identified
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