Faculty of Agriculture, Kyushu University, Fukuoka, 812 Japan
Telotrisomics or acrotrisomics are useful in determining chromosome arm location of genes. The genetic ratios obtained in the segregating progenies of telotrisomics or acrotrisomics are modified from that of disomics. When marker genes are located on telocentric or acrocentric arms, the genetic ratio obtained in the segregating progenies of telotrisomics or acrotrisomics are modified from 3: 1 in F2 and 1 : 1 in BC1F1. On the other hand, when the marker genes are located on the missing arms, these ratios are not modified. The arm location of genes, thus, can be decided by using telotrisomics or acrotrisomics.
MF\3\ 874, which we tentatively call modified Triplo 7, was obtained from the progenies of Triplo 7 spontaneously. It has 25 chromosomes and was found among trisomic plants from the segregating population of Triplo 7. The morphology of the plant was modified from Triplo 7 as well as from disomics, i.e. compact panicles, round spikelets, some of which look like dp (depressed palea). MF\3\ 874, however, did not show slender kernel and rolled leaves which characterized Triplo 7. The spikelets fertility of MF\3\ 874 is higher than Triplo 7 which is approximately 80 and 60% respectively.
In the present study, we observed modified segrecation ratios of some marker genes located on chromosome 7 when modified Triplo 7 was crossed with marker lines. The genetic segregation for the 6 tested markers are shown in Table 1. The F1 hybrids from all cross combinations were selfed to produce F2 populations. Among the 9 F2 populations analysed, the marker genes, d-6, g-1, spl-5 and v-11(t) gave trisomic ratio in the trisomic fraction. On the other hand, the marker genes, rfs and ge did not give the trisomic ratio in the trisomic fraction and in the pooled data (521 and 412). Moreover, the genetic ratios of rfs and ge fitted disomic ratio (1 : 2) more closely than the trisomic ratio (1 : 4) when the F3 progenies of plants showing normal phenotype in the disomic fraction of F2 populations were observed.
The linkage map of chromosome 7 was known to be d-6-g-1-spl-5-Rc-v-11 (t)-rfs. (Iwata et al. 1981, Satoh et al. 1984). Satoh and lwata (1990) reported that ge (giant embryo) was linked to v-11(t) (38.9%) and rfs (20.9%). They suggested the linkage map of chromosome 7 to be d-6-g-l-spl-5-Rc-v-11(t)-rfs- ge. The occurrence of somewhat many trisomics with rfs phenotype could not be
Table 1. Segregation of 6 marker genes located on chromosome 7 in type F2 and F3 progenies of acrotrisomic rice of AAa genotype =============================================================================== Line F2 or F3 Marker Disomics X2 for Trisomics X2 for No. gene ========== ================= =========== ================= + m Total 3:1 8:1 + m Total 3:1 44:1 =============================================================================== 404 F2 d-6 260 56 316 8.928** 13.981*** 59 1 60 17.422*** 0.085 402 F2 g-l 346 97 443 2.276 52.173*** 190 0 190 63.333*** 4.318* 527 F2 spl-5 100 15 115 8.768** 0.435 53 0 53 17.667*** 1.205 528 F2 spl-5 153 19 172 17.861*** 0.001 105 0 105 35.000*** 2.386 410 F2 v11-(t) 80 13 93 6.025* 0.774 57 0 57 19.000*** 1.296 401 F2 rfs 129 24 153 7.078** 3.243 52 6 58 6.644**17.611*** 527 F2 rfs 98 17 115 6.403* 1.570 49 4 53 8.610** 6.916** 521a F2 rfs 354 96 450 3.227 47.610*** 412a F2 ge 108 40 148 0.324 37.959*** 412 F2 ge 37 6 43 2.799 0.352 401 F3 rfs 48 80 128 1.000 b 24.500 c*** 412 F3 ge 16 22 38 1.316 b 11.605 c*** ============================================================================== *,** and ***: Significant at 5%, 1% and 0.1% levels, respectively. a): Pooled data including disomics and trisomics. b): X2 for 1:2. c): X2 for 1:4.considered with trisomic segregation. It may be noted that the breakpoint of chromosome 7 involved in MF\3\ 874 was close to the location of rfs and ge loci. Since no telocentric chromosome was observed in the mitotic cells, MF\3\ 874 may be an acrotrisomics for chromosome 7.
References
Iwata, N., H. Satoh and T. Omura, 1981. Linkage analysis by use of trisomics in rice (Oryza sativa L.). IV. Linkage groups locating on chromosomes 2 and 10. Jpn. J. Breed. 31 (Suppl. 1): 66-67. (In Japanese)
Satoh, H., N. Iwata and T. Omura, 1984. Linkage analysis in rice. On the loci of new virescent genes, v-9(t), v-10(t) and v-11(t). Jpn. J. Breed. 34 (Suppl. 1): 286-287. (In Japanese)
Satoh, H. and N. Iwata, 1990. Linkage analysis in rice. On three mutant loci for endosperm properties, ge (giant embryo), du-4 (dull endosperm-4) and flo-1 (floury endosperm-1). Jpn. J. Breed. 40 (Suppl. 2): 268-269. (In Japanese)