One set of recombinant inbred lines (RILs) derived from Japonica/Indica crosses of Asominori / IR24 (Tsunematsu et al. 1996) and its molecular data, kindly provided by Prof. A. Yoshimura (Kyushu University, Japan) was used to map QTLs associated with content of ferulic acid, which was one of allelopathic chemicals in rice (Chung et al., 2001; Matsuo, 2001). In this study, the RILs along with its parents, 'Asominori' and 'IR24', were grown at the experimental field of Miyazaki University, Japan during summer to autumn, 2002 with two replicates according to conventional methods. At maturity, the whole rice straw, consisting of stem and leaf, from each RIL plant was harvested, dried naturally and well ground. 4g straw powders was added in 20ml 99.7% HPLC grade methanol solutions and vibratedl 120 times at a minute in water baths (40^o) for 24hr, then centrifuged at 3000rpm for 15min. The solvent were filtered through 0.20_ HYDROPHILIC filter before HPLC analysis. The identification of ferulic acid in rice straw was conducted with the HPLC analysis as described by Fujii et al. (1991) and their contents were calculated through comparing peak areas. All measurements for each line were replicated two times and the average values were used for quantitative trait loci (QTL) analysis. QTL analysis was performed by QTL Cartographer computer program software (Wang et al., 1999) version 1.13g through composite interval mapping model. The loci with LOD value greater than 2.0 was considered as indicative of the presence of a QTL.

As a result, the both parents, Asominori (94.3 micro g^-1) and IR24 (29.7 micro g^-1) show great differences of ferulic-acid content in rice straw and the former was much higher than in the latter. In addition, continuous variation and transgressive segregation were observed, which suggested that the content of ferulic acid was quantitatively inherited in this population.

Three QTLs were identified for the content of ferulic acid with LOD value of 2.03 (chromosome 3), 3.16 (chromosome 6) and 3.06 (chromosome 7) (Table 1 and Figure 1) and had increased additive effects of 13.5, 18.3 and 18.1 micro g^-1 from Asominori parent, respectively. This is the first report on the identification of QTL associated with phenolic chemicals, which were related to plant allelopathy, and their chromosomal localization on the molecular map of rice. The results and the tightly linked molecular markers that flank the QTL might be useful

in breeding for allelopathy in rice.

Acknowledgement

We are greatly indebted to Professor A. Yoshimura (plant breeding laboratory, Agricultural faculty of Kyushu University, Japan) for kindly providing materials, molecular data and valuable advices. We want to thank Japan society for the promotion of science (JSPS) providing the first author to postdoctoral fellowships.

References

Chung, I.M., J.K. Ahn and S.J. Yun. 2001. Identification of allelopathic compounds from rice (Oryza sativa L.) straw and their biological activity. Canadian Journal of Plant Science. 81: 815-819.

Fujii, Y., T. Shibuya, T., Yasuda, T. Ootani and M. Furukawa, M., 1991. Analysis of phenolic acids from soil and plants by high-pressure liquid chromatography. Japanese Journal of Soil and Fertilizer. 62: 529-532 (in Japanese).

Indejiti, 1996. Plant phenolic in allelopathy. Bot. Rev. 62: 186-202.

Matsuo, M., 2001. Studies on allelopathy in rice and its bioassay methods. Ph.D. diss. Kagoshima University, Japan. pp.111-130 (in Japanese).

Tsunematsu, H., A. Yoshimura, Y. Harushima, Y. Nagamura, N. Kurata, M. Yano and N. Iwata. 1996. RFLP framework map using recombinant inbred lines in rice. Breeding Science 46: 279-284.

Wang, S.C., B.Z. Zeng and C.J. Basten. 1999. QTL cartographer windows version 1.13g (Programmed, 30 Aug.1999). http://statgen.ncsu.edu/qtlcart/cartographer.html. (Verified, 15. Aug, 2001).