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To fully exploit the genetic potential of African rice, Oryza glaberrima Steud., we aimed at developing a series of O. glaberrima introgression lines (GILs) in the back-ground of Japonica rice (O. sativa L. cv. Taichung 65). Each GIL carrying homozygous chromosome segments from O. glaberrima will be selected using RFLP markers. As a first step, an RFLP Iinkage map based on backcross population (BC1F1) was constructed. QTLs for two quantitative traits, male sterility and heading date, were investigated in the BC2F1 population. The RFLP map contained 101 well-dispersed RFLP markers. Total map length was 1403.4 cM. Linkage arrangement of the RFLP markers was in good agreement with that of the previously constructed maps. Significant segregation distortions were observed in chromosomes 4, 5, 6 and 11. In chromosome 6, a strong distortion towards O. glaberrima was found. On chromosomes 1, 6 and 10, significant (

Recombinant inbred (RI) Iines of rice (Oryza sativa L.) were developed from a cross of Asominori x IR24 by the single seed descent method. Seventy-one RI Iines of the F6 and F7 generations were used for RFLP mapping. RFLP framework map constructed using the RI lines covered a distance of 1275cM containing 375 markers. All the twelve linkage groups were assigned to their respective chromo-somes. The RI Iines showed a distorted segregation in some regions of chromosomes 1, 3, 6, 11 and 12. Heterozygous loci in the lines still remained. Average frequency of the heterozygous region was 3.6% with a range of O% - 19.3% in F6 and 1.9% with a range of O% - 5.5% in F7. The RFLP map corresponded well to the previous maps constructed using F2 populations (Saito et al. 1991, Kurata et al. 1994) and the two previous maps were integrated in detail. The RFLP framework map and RI Iines developed in this study will be useful for further accumulation of molecular markers and analysis of quantitative trait loci.

Four aneuhaploids (2n = 13) and 5 tetrasomics (2n = 26) of rice (Oryza sativa L.), which were obtained through anther culture of trisomics (2n = 25), were examined by Southern hybridization analysis to identify their extra chromosomes, to test their genetic stability, and to demonstrate their utility in genome alaysis. Twenty-one RFLP markers located on 9 chromosomes were used as probes. Extra chrounosome identification was conducted by observing dosage changes of the probes in the aneuhaploids and tetrasomics. The results indicated that the extra chromosomes of the aneuhaploids and tetrasomics were identical to their parental trisomics. The aneuhaploids and tetrasomics used in the study are genetically stable, except the aneuhaploid plant derived from the trisomic with an extra chromosome 5. This plant showed clear DNA variation. Chromosome assignment of unnrapped DNA clones was tried by using the identified aneuploids. The result showed that aneuhaploids and tetrasomics are useful materials for genome analysis in rice to assign cloned DNA fragments to specific chromosomes.

In the inoculation tests on rice cultivars using Philippine races of bacterial blight (BB) caused by Xanthomonas campestris pv oryzae, we found that Taichung Native 1 (TN1) was resistant only to race 5 (PXO112) and susceptible to races 1, 2, 3, 4, and 6. This kind of reaction pattern to BB pathogens has not been found in any other rice cultivar resistant to BB in Japan and at the International Rice Research Institute in the Philippines. Therefore, it was suggested that TN1 has a new gene for resistance to BB. The mode of inheritance of resistance in TN1 to race 5 was studied. The analysis of the F 1 plants, the F 2 populations, and the backcross progeny from the crosses between TN1 and susceptible cultivars revealed that the resistance of TN1 was controlled by a single dominant gene. Thus this new resistance gene was designated as Xa-14.

We have constructed a genetic map of the nuclear genome in rice (Oryza sativa L.), utilizing 322 restriction fragment length polymorphism (RFLP) DNA markers and nine morphologlcal and biochemical genetlc markers. The RFLP map is based on the segregation of 144 F2 plants from a cross between Indica and Japonica varieties. The map covers a total of 1, 836 cM with 347 loci and exceeds the data recorded in the classical genetic map of rice by 58.5% and the current RFLP map (McCOUCH et al. 1988) by 32.2%. The RFLP linkage groups were assigned to the twelve chromosomes of rice using trisomic mutants andseveral genetic markers. This map should provide the basis for the mapping of genes controlling agronomic traits of rice.

To increase the genetic resources for resistance to bacterial blight (BB) caused by Xanthomonas campestris pv, oryzae in rice, we initiated a study to induce mutants with resistance to BB by chemical mutagen. Fertilized eggs of a susceptible cultivar, IR24 to Philippine BB races were treated with N-methyl-N-nitrosourea (MNU) at the singie-cell stage of embryogenesis. The panicles of F1 plants were bagged before flowering to avoid any outcrossing. M2 lines, derived from each M1 plant, were inoculated with a Philippine BB race 5 (isolate PXO 112) at the seedling stage. As a result, out of 2, 739 M2 lines tested, two resistant mutant lines were found and they were designated XM5 and XM6. M3 progenies derived from M2 plants in both mutant lines were tested for segregation for resistance. The results suggested that resistance of these mutant lines was induced by the MNU treatment. The mutation frequency of BB resistance was 7.30 × 10-4. (no. of resistant mutant lines/no. of tested M2 lines). Both of the mutant lines showed resistant to all six known Philippine BB races. We crossed these two resistant mutant lines with IR24 to clarify their inheritance of resistance. The reaction of F1 hybrids and F2 populations to BB races suggested that both mutant lines have single recessive genes for BB resistance.

In an earlier study (TAURA et al. 1991), XM5, a mutant line of rice induced by Nmethyl-N-nitrosourea, was confiruled to carry a single recessive gene resistant to all known Philippine races of bacterial blight (BB) caused by Xanthomonas campestris pv. oryzae. To clarify the allelic relationships between the resistance gene of XM5 and the three known recessive genes, xa-5, xa-8, and xa-13, F1 plants and F2 populations from the crosses between XM5 and rice cultivars carrying the known recessive genes were analyzed with Philippine BB races. Results showed that the recessive resistance gene of XM5 is not allelic with the three known recessive genes, xa-5, xa-8, and xa-13. Thus we concluded that the resistance gene of XM5 is a new one, and designated it as xa-19, following the rule of gene symbolization of the Rice Genetics Cooperative.

The reciprocal translocation method was employed, for the most part, to conduct linkage studies in rice plants. Thirty reciprocal translocation lines, thirteen marker genes and the C type trisomics were use in this study. A gene for round kernel was identified and designated as rk2. It was found that the marker genes, d1 (linkage group VI), nl1 (IX) and ri (IX) were associated with chromosome 2. Therefore, the results supported the early studies on the integration of the linkage groups VI and IX by the trisomic method. The linkage group III to which eg, spl6' lax and d10 belong corresponded to chromosome 3. It was found that a gene, d18' was located also on chromosome 3. A gene for spotted leaf, spl1' which was found as one of the genes composing a new linkage group by IWATA and OMURA (1975), was located on chromosome 4, and it was also suggested that rl1 and nal2 were located on the same chromosome. The three genes, fl, pgl and rk2, were shown to be located on chromosome 7.