Abstract: Previous study showed that genetic drag between a blast resistance gene Pi25 (t) and QTLs conditioning spikelet fertility (qSF-6) and number of filled grains per panicle (qNFGP-6) were detected on the short arm of rice chromosome 6. To further verify, a larger population was used for analysis and the results confirmed the genetic drag between the blast resistance and spikelet fertility (SF) but no genetic drag was detected between the blast resistance and number of filled grains per panicle (NFGP). Breakdown or avoidance of the genetic drag could be achieved by selection against the background genotype of a heading-date gene (qHD-7) that resided in the region between RM2 and RM214 on chromosome 7. To further validate, two lines with almost identical genotypes on all chromosomal regions except the Pi25 (t) region on chromosome 6 were chosen to develop a new population. The results showed that qSF-6 could be further subdivided into qSF-6-1 and qSF-6-2. When the genotype of RM2-RM214 region was from rice variety Zhong 156, genetic drag between Pi25 (t) and SF (qSF-6-2) was detected, and the allele of qSF-6-2 from rice variety Gumei 2 reduced SF. When genotype of the region between RM2-RM214 was from Gumei 2, no genetic drag was detected. The results indicated that genetic drag between the blast resistance and spikelet fertility could be broken down or avoided under a certain background genotype based on the selection against heading-date and provided a marker aided solution for high level of blast resistance and yield breeding in rice and other crops as well.

Key words: rice, Oryza sativa, genetic drag, blast resistance, quantitative trait locus, heading date

摘要： 利用重组自交系研究表明，在水稻第6染色体短臂上稻瘟病抗性基因Pi25(t)与控制结实率和每穗实粒数的QTL之间存在遗传累赘。为了验证这种关系，采用了更大的遗传群体进行分析，结果表明稻瘟病抗性与结实率存在遗传累赘，但未检测到稻瘟病抗性与每穗实粒数存在遗传累赘。通过对第7染色体长臂RM2-RM214区间抽穗期基因（qHD7）型背景进行选择，可以打破或避免稻瘟病抗性与结实率的遗传累赘。为了进一步验证这种关系，选择Pi25(t)区间基因型不同、RM2-RM214区间基因型相同、其他染色体区间基本一致的两个株系发展新群体进行分析，除第6染色体的结实率QTL可以分解成2个效应较小的QTL（qSF61和qSF62）外，当第7染色体RM2-RM214区间基因型为中156背景时，Pi25(t)与结实率QTL（qSF62）存在遗传累赘，且qSF62来自父本谷梅2号的等位基因起减效作用；当第7染色体RM2-RM214区间基因型为谷梅2号背景时，第6染色体上没有检测到结实率QTL。上述结果说明在特定育种材料中对抽穗期基因进行选择可以成功打破或避免稻瘟病抗性与结实率的遗传累赘，为水稻以及其他作物的高产抗病育种提供了一种新途径。

关键词: 水稻, 遗传累赘, 稻瘟病抗性, 数量性状座位, 抽穗期