Interspecific backcross progenies were developed from a cross between elite japonica cultivar Hwaseongbyeo, used as a recurrent parent, and the wild species Oryza grandiglumis (IRGC Acc. No. 101154) with CCDD genome used as a donor parent. Among them, one BC₅F₆ introgression line (HG101) was selected. HG101 was produced from a single plant from BC₅F₃ population. It was subsequently self-pollinated for three more generations. HG101 resembled the O. sativa parent, Hwaseongbyeo, but differed in a number of traits including culm length, days to heading, grain shape, number of spikelets per panicle (Ahn et al. 2001). These differences between HG101 and Hwaseongbyeo can be attributed to the O. grandiglumis chromosome segments introgressed into HG101. The most notable feature of HG101 is the absence of undesirable traits of the O. grandiglumis, such as grain shattering and tall plant stature.

To detect the introgressions, 300 SSR markers of known chromosomal position have been screened among the parents and HG101 (Temnykh et al. 2001). Of the 300 SSR markers, 19(6.3%) produced O. grandiglumis-specific alleles in HG101 and at least eleven introgressed chromosome segments were detected on chromosomes 3, 7, 8, 9, 11, and 12 (Ahn et al. 2001). Five introgressed segments were detected by pairs of adjacent SSR markers. Six segments were detected by single SSR markers, and the flanking markers were negative for introgression.

To detect the effects of these segments on the agronomic traits, 150 F_2:3 lines derived from cross between Hwaseongbyeo and HG101 were evaluated for culm length and grain length (Fig. 1). The field planting followed a randomized complete block design with two replications. Each plot consisted of thirty plants planted in a single row with 15-cm spacing between plants and 30-cm spacing between rows. Phenotypic data were collected from the

middle 10 plants for he following traits: (1) Culm length in centimeters measured from the soil to the panicle neck of the main culm, excluding the awns. (2) Grain length in grams measured on fifty r brown grains randomly selected from each plant. Means over replications were calculated for each trait and used in data analysis. To detect association of introgression with the two traits, single point analysis was employed. Regions of the genome were identified as putatively containing a QTL if a significant effect (P < 0.005) was observed for a single marker/ trait combination at a single location. Significant putative QTLs were identified for culm length and grain length (Table 1). For culm length, O. grandiglumis allele decreased culm

length at cl8.1 and cl11.1, which explained 10.1% and 23.2% of the total variation, respectively. These alleles have not been detected in previous QTL studies between Oryza cultivars, indicating potentially novel alleles present in O. grandiglumis. The QTLs detected in this study might provide a rich source of information on the natural genetic variation underlying the evolution and breeding of rice.

To our knowledge, this report is the first genetic study conducted on an interspecific cross involving the wild species O. grandiglumis.

Acknowledgements

This study is a part of the BioGreen21 supported project, "Improvement of Selection Efficiency and Development of New Rice Cultivars Using Molecular Markers".

References

Ahn, S.N., S.J. Kwon, J.P. Suh, K.H. Kang, H.Y. Kim, M.T. Song, H.G. Hwang, and H.P. Moon, 2001. Identification of introgressions in a backcross progeny derived from the interspecific cross between Oryza sativa and O. grandiglumis. Korean J. Breedi. 33: 318-323.

Temnykh, S., G. DeClerck, A. Lukashova, L. Lipovich, S. Cantinhour and S.R. McCouch, 2001. Computational and Experimental Analysis of Microsatellites in Rice (Oryza sativa L.): Frequency, Length Variation, Transposon Associations, and Genetic Marker Potential. Genome Res. 11:1441-1452.