25. RFLP mapping of genes controlling heading date found in Oryza glumaepatula Steud. introgression lines in rice

Plant Breeding Laboratory, Faculty of Agriculture, Graduate School, Kyushu University, Fukuoka, 812-8581 Japan

Days to heading (DTH, the number of days from sowing to emergence of the first panicle) is an important agronomic trait because it determines the maturity in rice. To determine the chromosomal locations of the genes controlling heading date, backcrossed populations (BC4F2) from a cross between Taichung 65 (TC65) and Oryza glumaepatula Steud. (IRGC Acc. No. 105668) were utilized (Sobrizal et al. 1999). BC4F2 271 and 204 populations, which exhibited wide variation in days to heading were planted under natural daylength condition in the paddy field of Kyushu University Experiment Station, Fukuoka, Japan. Seeds were sown on May 28, 1999 and transplanted on June 28, 1999. Each plant was monitored for the appearance of the first panicle. Leaves were collected from each plant after heading, for DNA extraction. One hundred six RFLP markers showing polymorphism between O. glumaepatula and TC65 were used for the whole genome survey in BC3F1 generation. The retained heterozygous regions were further evaluated in BC4F1 and BC4F2 generations (Fig. 1A).

The frequency distributions for DTH of BC4F2 271 and BC4F2 204 populations are shown (Fig. 1B). The DTH of TC65 ranged from 95 to 100 days whereas BC4F2 271 ranged from 85 to 101 days and BC4F2 204 ranged from 94 to 117 days. BC4F2 271 headed earlier than TC65. BC4F2 204 headed late compared to the previously reported backcrossed populations, BC4F2 254 and BC4F2 222 carrying Lhd1(t) and Lhd2(t) genes, respectively (Sanchez et al. 2000). The variations of heading in BC4F2 271 could be attributed to the additive effect of O. glumaepatula and TC65 alleles. DTH variation in BC4F2 204 was mainly due to partial dominance effect of O. glumaepatula allele (d/a=0.55).

To map the genes, the phenotypic and RFLP data of both populations were analyzed using MAPMAKER/QTL v.3.0. Results showed the early heading gene was linked to RFLP marker C234 on chromosome 10 (Fig. 1C). This early heading gene was designated as qEhd1(t). The position of qEhd1(t) gene on chromosome 10 is within the vicinity of a previously reported heading gene, Ef (t) (Doi and Yoshimura, 1998). qEhd1(t) promotes early heading by about 10 days under natural daylength condition, as compared to TC65.

The recessive late heading gene from O. glumaepatula was mapped between RFLP markers C560 and R759 on chromosome 2 (LOD 18.0). The distance between the two RFLP markers was 5.4 cM (Fig. 1C). This late heading gene was designated as qlhd3(t). The position of qlhd3(t) on chromosome 2 was similar to the region of the previously reported gene, Hd7(Shimizu et al. 1997). qlhd3(t) significantly delayed DTH by about 12 days, under natural daylength condition, as compared to Lhd1(t) and Lhd2(t).

To determine the genetic interactions among the retained regions on chromosomes 1, 2, 7, 8 and 10, one- and two-way analysis of variance (ANOVA) was performed (data not shown). The results indicate the absence of interaction among the regions.

This study was supported in part by Bio-oriented Technology Research Advancement Institution (BRAIN), Japan.


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