Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2013
Publication Date: 3/2/2013
Citation: Eizenga, G.C., Prasad, B., Jackson, A.K., Jia, M.H. 2013. Identification of rice sheath blight and blast quantitative trait loci in two different O. satival/O. nivara advanced backcross populations. Molecular Breeding. 31(4):889-907. doi: 10.1007/s11032-013-9843-y.
Interpretive Summary: Sheath blight and leaf blast are the most prevalent fungal diseases of cultivated rice and cause significant economic damage to rice production worldwide. No source of complete resistance to sheath blight disease has been identified in cultivated rice (Oryza sativa), whereas in the case of blast disease, the resistance genes are often overcome, thus new sources of resistance genes are always needed. The wild Oryza species which are closely related to cultivated rice, are a potential source of important traits including new resistance genes to fight pests like sheath blight and blast diseases. O. nivara is the wild species progenitor of cultivated rice and grows throughout Southeast Asia. The objective of this research was to identify the chromosomal location(s) of possible new sheath blight and blast resistance genes in two O. nivara accessions collected in Orissa (IRGC100898) and Maharashtra (IRGC104705), India. Both accessions demonstrated moderate resistance to sheath blight disease and resistance to blast disease in previous experiments. In this study, we began the process of identifying these potential resistance genes and transferring them into the popular southern U.S. medium grain variety, Bengal. One major region was identified as associated with the potential sheath blight resistance genes contributed from the O. nivara parent using both accessions, suggesting a novel sheath blight resistance gene may be present in this region. A different chromosomal region was identified as associated with a potential leaf blast resistance gene(s) contributed by the O. nivara parent using both accessions. Efforts are underway to continue incorporating these potential sheath blight and blast resistance genes into Bengal and develop adapted, resistant lines to be made available to rice breeders for use in the development of rice varieties with superior disease resistance for the U.S. rice industry.
Technical Abstract: Two accessions of the rice (Oryza sativa) wild ancestral species, O. nivara identified as being moderately resistant to sheath blight and leaf blast diseases, were used as donor parents to develop two advanced backcross populations with the U.S. rice cultivar, Bengal, as the recurrent parent. The O. nivara donor parent for ‘Wild-1’ (252 BC2F1 lines) was acc. IRGC100898 and for ‘Wild-2’ (253 BC2F1 lines) was acc. IRGC104705. Both populations were genotyped with 131 SSRs and linkage maps covered 1567.5 cM (Wild-1) and 1312.2 cM (Wild-2). Sheath blight (ShB) disease was evaluated in both greenhouse and field conditions. Days to heading (DH), plant height (PH), and plant type (PT), confounding factors for sheath blight disease under field conditions, were recorded. Leaf blast disease was rated under greenhouse conditions. Multiple interval mapping identified qShB6 with resistance to sheath blight disease attributed to the O. nivara parent in the greenhouse. In the field, qShB6 was the most significant ShB-QTL in all trials with resistance attributed to O. nivara. Also, qShB1 and qShB3 were identified in all trials but were not always attributed to the same parent. The qShB6 QTL is in the same region as DH-QTL, qDH6, and qShB1 is in the same region as the major PH-QTL, qPH1, suggesting these ShB-QTL may be confounded by other traits. Although qShB3 did not have as large effect as other loci, it was not confounded by either HD or PH. For leaf blast, qBLAST8-1 was found in both populations providing resistance to races IB1 and IB49, whereas qBLAST12 was only in Wild-2. Resistance was attributed to O. nivara for both QTLs and blast resistance genes have been reported in this region previously.