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Title: Bacterial panicle blight resistance QTL in rice (Oryza sativa L.) and their association with resistance to other diseases

item Pinson, Shannon

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2009
Publication Date: 7/1/2010
Citation: Pinson, S.R., Shahjahan, A., Rush, M.C., Groth, D.E. 2010. Bacterial panicle blight resistance QTL in rice (Oryza sativa L.) and their association with resistance to other diseases. Crop Science. 50:1287-1297.

Interpretive Summary: Rice panicle blight disease was considered by U.S. rice producers to be a sporadic and minor problem until it reached epidemic proportions in 1995. Not even the cause of this disease was known at the time, so no control measures existed. Panicle blight continued to affect up to 60% of the southern U.S. fields over the next several years. During this same time, scientists in Louisiana were culturing strains of bacteria collected from field-grown rice with the aim of developing biopesticides by finding bacteria antagonistic to the fungal pathogens that cause rice sheath blight and rice blast diseases. This led to the fortuitous discovery of Burkholderia glumae as the underlying cause of what is now called bacterial panicle blight (BPB). An inoculated field-nursery screening technique for comparing the BPB resistance of various rice varieties was soon developed. This study utilized that newly developed screening technique to learn more about the rice genes that confer resistance to BPB. A rice gene-mapping population that had previously been used to identify genes for resistance to three other diseases (sheath blight, blast, and bacterial leaf blight) was chosen for the present study because the location and genetic effect of the newly identified BPB resistance genes could then be readily compared to the previously identified disease resistance genes. We determined that BPB resistance is controlled by as many as 14 genes, each with relatively small individual effect. Nine of the 14 resistance alleles we discovered came from the more-resistant foreign rice parental line, but five of them came from the parental line that is representative of typical southern U.S. rice. Four of the BPB resistance genes were located in the same genomic regions previously found to contain genes for resistance to other rice diseases. This suggests, but does not prove, that these genes may be part of a general disease response system within the plants. The rice population we observed flowered over a 3-month period, and late heading time also appeared to be associated with BPB resistance. While this association could be due to genetic linkage between heading and BPB genes, it might also be that the late-flowering plants were not resistant per se, but were flowering under cooler temperatures which were less conducive to bacterial growth. Because of this, the BPB genes we report should be verified in further study before being considered conclusive. This study comprises the first-ever report of BPB resistance genes, and provides important knowledge that will direct and speed the progress of the further investigations into BPB resistance genes.

Technical Abstract: Bacterial panicle blight (BPB) of rice (Oryza sativa L.) occurs when the bacterium Burkholderia glumae infects and colonizes emerging and flowering panicles, causing kernels to abort. To identify quantitative trait loci (QTL) for BPB resistance, a population of 300 recombinant inbred lines (RILs) derived from ‘Lemont’ x ‘TeQing’ were evaluated in 2001 and 2002 for resistance to BPB in field plots spary-inoculated with B. glumae at the time of flowering. Because this same RIL population had been previously used to map QTL for three other diseases, use of this population in the present study allowed direct comparison between the presently and previously identified disease resistance QTL. Composite (CIM) and Multiple Interval Mapping (MIM) using QTL Cartographer v2.5 revealed a total of 14 BPB-QTL, with five resistance alleles coming from the susceptible U.S. rice parent, Lemont, and nine resistance alleles coming from the more resistant Chinese cultivar, TeQing. Four BPB-QTL were co-located with QTL previously identified as providing resistance to one or multiple other diseases. Three of the BPB-QTL were also associated with late flowering. Because late flowering panicles are subjected to cooler temperatures that are less conducive to disease development during grain fill, it is possible that the genetic effects of the heading-related QTL were biased. The present data could not distinguish between pleiotropy and close linkage of the BPB-QTL with the previously identified heading and disease resistance QTL. It is suggested that these BPB-QTL be verified with further study using germplasm and/or evaluation techniques that are less confounded with heading time.