11. Acrotrisomics with chromosome 7 in rice

H. YASUI and N. IWATA

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)