A "defeated" rice resistance gene acts as a QTL against a virulent strain of Xanthomonas oryzae pv. oryzae |
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Authors: | Li Z K Luo L J Mei H W Paterson A H Zhao X H Zhong D B Wang Y P Yu X Q Zhu L Tabien R Stansel J W Ying C S |
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Institution: | (1) Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77843-2474, USA, US;(2) Chinese National Rice Research Institute, 359 Tiyuchang Road, Hangzhou, 310006, China, CN;(3) Texas A&M University System, Agricultural Research and Extension Center, Route 7, Box 999, Imes Rd., Beaumont, TX 77713, USA, US |
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Abstract: | The genetic components responsible for qualitative and quantitative resistance of rice plants to three strains (CR4, CXO8,
and CR6) of Xanthomonas oryzae pv. oryzae (Xoo) were investigated using a set of 315 recombinant inbred lines (RILs) from the cross Lemont (japonica) × Teqing (indica) and a complete linkage map with 182 well distributed RFLP markers. We mapped a major gene (Xa4) and ten quantitative trait loci (QTLs) which were largely responsible for segregation of the resistance phenotype in the
RILs. The Teqing allele at the Xa4 locus, Xa4
T
, acted as a dominant resistance gene against CR4 and CXO8. The breakdown of Xa4
T
-associated resistance mediated by the mutant allele at the avrXa4 locus in the virulent strain CR6 results from significant changes in both gene action (lose of dominance) and the magnitude
of gene effect (≈50% reduction). Nevertheless, Xa4
T
still acted as a recessive QTL with a significant residual effect against CR6. The mutant alleles at the avrXa4 locus in CXO8 and CR6 that lead to a reduction in effect, or “breakdown”, of Xa4
T
were apparently accompanied by corresponding penalties for their fitness. The quantitative component of resistance to Xoo in the RILs was largely due to a number of resistance QTLs. Most resistance QTLs mapped to genomic locations where major
resistance genes and/or QTLs for resistance to Xoo, blast and sheath blight were identified in the same cross. Most QTLs showed consistent levels of resistance against all
three Xoo strains. Our results suggest that a high level of durable resistance to Xoo may be achieved by the cumulative effects of multiple QTLs, including the residual effects of “defeated” major resistance
genes.
Received: 28 April 1998 / Accepted: 9 October 1998 |
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Keywords: | Oryza sativa L Gene mapping Quantitative trait loci (QTLs) Host-pathogen co-evolution Stabilizing selection |
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