RFLP mapping and race specificity of bacterial blight resistance genes (QTLs) in rice

By using a set of 315 recombinant inbred lines (RILs) from the cross Lemont (japonica)×Teqing (indica) and a complete linkage map with 186 well distributed RFLP markers and 3 morphological markers, a major gene (Xa4) and 10 QTLs and 9 pairs of epistasis loci conferring horizontal resistance to three strains of \%Xanthomonas oryza\% pv \%oryza (Xoo)\% were mapped. The Teqing allele at Xa4 on chromosome 11 acts as a dominant resistant gene against pathogen race CR4 and CX08, but as an additive QTL with a significantly (47%) reduced effect \{against the\} virulent strain, CR6. The major gene Xa4 exhibited stronger degree of race specificity. Most QTLs showed consistent levels of resistance against all three \%Xoo\% strains. The results suggest that a high level durable resistance to \%Xoo\% may be achieved by cumulative effects of multiple QTL.

水稻白叶枯病数量抗性座位定位及其小种专化性

用水稻白叶枯病3个毒力不同的菲律宾小种P2、P6和P9，对供体Lemont导入到特青背景的178个近等基因导入系群体，进行白叶枯病数量抗性座位（quantitative resistance loci，QRL）定位及其小种专化性研究。供试亲本Lemont感3个小种，特青中感P2和P9，感P6。导入系群体的病斑长度呈连续正态分布。共发现影响病斑长度的10个主效QRL和12对互作QRL，除第6染色体上的QBr6c外，所有位点上的Lemont等位基因均增加了病斑长度（即降低了抗病性）。在第11染色体RM144～RM123区间检测到1个主效QBr11，推测为Xa4基因，对P2和P9表现为主效QRL，但完全被P6克服，在该位点未能检测到任何抗性残余效应。主效和互作QRL对不同小种具有不同的抗性反应，存在明显的小种专化性，虽然有些QRL对不同小种的互作方向一致，但互作效应存在着数量差异。由于在感病亲本中检测到较多的主效和互作QRL，这些QRL之间的相互作用及其效应的累加，有利于寄主与病原菌小种之间的稳定化选择，共同增强寄主抗病性及稳定性效应。