The gleyic paddy soils are widely distributed in China, Srilanka, India, Indonesia, Sierra Leone, Libya, Nigeria, Columbia and Philippines(Mahadavappa 1979, Yoshida, 1981). In China, the gleyic paddy soils are estimated to cover 7.5 to 8.0 million hectares, where ferrous iron toxicity is reported to reduce rice yield by 10%-20 % depending on the intensity of toxicity and the tolerance of the rice cultivar(Li et al. 1991) .

Eighty-one recombinant inbred lines (RILs) deriver from a cross of Kinmaze / DV85 were used for molecular mapping of QTLs for some traits associated with tolerance to ferrous iron toxicity in rice. RILs, along with their parents and control cultivars IR26 IR64, IR74 Mashuri and Suakoko8 were screened for ferrous iron tolerance at Nanjing Agricultural University from June 10 to July 7, in 2002 . Leaf bronzing index and plant height were measured after 4 weeks of solution culture experiment.

The distributions of the leaf bronzing index and plant height of the RILs are shown in Figure 1 . For the leaf bronzing index counted there is clear difference between Kinmaze and DV85, but there isn't very clear difference in plant height between two parents .

Interval mapping of QTL using the computer package Mapmaker/QTL(Lincoln et al.1993) with threshold LOD>3.0, identified QTLs associated with tolerance to ferrous iron toxicity in rice. A total of three QTLs were detected on chromosome 3 (Fig. 2, Table 1), with LOD of QTLs ranging from 3.79 to 5.89 . Two QTLs controlling leaf bronzing index was located at the region of XNpb279-C25 and XNpb144-XNpb362 on chromosome 3, and their contribution

to whole variation were 17.38 % and 22.07 %, respectively .Kinmaze alleles in these regions reduced the leaf bronzing index on the heterozygous condition by 0.05 and 0.06, repectively. One QTL controlling plant height was located at the region of R1468A-R1468B on chromosome 3, with contribution of 23.18 % to whole variation. Kinmaze alleles in these regions increased plant height In this study, as the leaf bronzing index is indicated as a phenotypic value for tolerance to ferrous iron toxicity, the QTL located at the region of XNpb279-C25 for leaf bronzing index on chromosome 3 coincided with the QTLs for chlorophyll content which located at the region of C515-C25 on chromosome 3 on a rice function map (Ishimaru et al. 2001).

References

Ghosh. A. K, S. Sen, and S. Palit, 1991. Comparative efficacy of chlorophyllin in reducing cytotoxicity of some heavy metals . Biometal 4: 158-16.

Ishimaru. K, M. Yano, N. Aoki, K. Ono, T. Hirose, S. Y. Lin, L. Monna, T. Sasaki, and R. Ohsugi, 2001. Toward the mapping of physiological and agronomic characters on a rice function map: QTL analysis and comparison between QTLs and expressed sequences tags . Theor. Appl. Genet. 102: 793-800.

Li D. M., J. J.Tang, and Y.S.Li, 1991. The eco-physiological mechanism of rice tolerance for gleyic soil stress and the breeding of varieties tolerance for soil-related Stress. Rice Review and Abstracts 10: 1-4 .

Lincoln. S.E., M.J. Daly, and E.S.Lander, 1993. Mapping genes controlling quantitative traits using MAPMAKER/QTL version 1.1: a tutorial and reference manual, 2^nded . Cambridge Mass : Whitehead Institute for Biometrical Research. Cambridge, USA.

Mahadavappa M., 1979. International Rice Research of Plant Science, NO. 43, International Rice Research Institute. Manila, Philippines.

Yoshida S., 1981. Fundamentals of Rice Crop Science, International Rice Research Institute. Manila, Philippines.