Abstract
BackgroundBacterial grain rot (BGR), caused by the bacterial pathogen Burkholderia glumae, is a destructive disease of rice. Because BGR tends to be highly affected by environmental conditions such as temperature and humidity, it is difficult to evaluate BGR resistance of diverse cultivars with different heading dates by using field inoculation. Molecular tagging of genes involved in BGR is an important objective for rice breeding.ResultsIn this study, we mapped a quantitative trait locus (QTL) for BGR resistance by a modified cut-panicle inoculation method. First, we assessed the levels of BGR resistance in 84 cultivars by a standard cut-panicle inoculation technique, in which panicles are harvested and inoculated in the laboratory under controlled conditions. For the genetic analysis, we selected two cultivars: Kele, a resistant traditional lowland cultivar (indica) that originated in India, and Hitomebore, a susceptible modern lowland cultivar (temperate japonica) from Japan. Second, by comparing the susceptibility of Kele and Hitomebore spikelets before and up to 3 days after anthesis, we found a dramatic decline in susceptibility at 1 day after anthesis in Kele but not in Hitomebore. Thus, we applied a modified method by inoculating spikelets at 1 day after anthesis for further analysis. To search for QTLs associated with BGR resistance, we measured the ratio of diseased spikelets (RDS, an index reflecting both quantity and severity of infection) and the ratio of diseased spikelet area (RDSA) in 110 backcrossed inbred lines (BILs) derived from a cross between Kele and Hitomebore. One major QTL associated with both RDS and RDSA was detected on the long arm of chromosome 1. This QTL explained 25.7% and 12.1% of the total phenotypic variance in RDS and RDSA in the BILs, respectively, and the Kele allele increased BGR resistance.ConclusionsWe mapped a major QTL for BGR resistance on the long arm of chromosome 1. These results clearly demonstrated that genetic analysis of BGR resistance in rice can be effectively performed and that this trait could be a target of marker-assisted selection in rice breeding programs.Electronic supplementary materialThe online version of this article (doi:10.1186/1939-8433-6-13) contains supplementary material, which is available to authorized users.
Highlights
Bacterial grain rot (BGR), caused by the bacterial pathogen Burkholderia glumae, is a destructive disease of rice
Screening cultivars for BGR resistance by cut-panicle inoculation We measured the levels of BGR resistance of 84 rice cultivars by the standard cut-panicle inoculation method (Figure 1A)
The inoculated spikelets were imaged by using a scanner and ratio of diseased spikelet area (RDSA) was calculated by SmilePlant (Software of Measuring Image for Lesion Estimation), which we developed for this analysis
Summary
Bacterial grain rot (BGR), caused by the bacterial pathogen Burkholderia glumae, is a destructive disease of rice. Burkholderia glumae causes bacterial grain rot (BGR) and seedling rot in rice (Oryza sativa L.), which are increasingly important diseases in global rice production (Ham et al 2011b). In the southern United States, yield losses caused by outbreaks of BGR in rice fields in Louisiana were as much as 40% in 1995 and 1998; significant losses caused by this disease were experienced in more recent years (Ham et al 2011a; Ham et al 2011b; Nandakumar et al 2009; Shahjahan et al 2000; Zhou et al 2011). BGR in rice occurs by both primary and secondary infection (Tsushima 1996; Tsushima et al 1991; Tsushima et al 1996). Primary infection occurs when seeds contaminated with B. glumae are sown and transplanted into fields, and seedling rot appears in some infected plants. The infection may cause unfilled or aborted grains (Ham et al 2011b)
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