51. Location of a gene for wide-compatibility in the RFLP linkage map

Aimin LIU1, Qifa ZHANG2 and Hebiao LI1

1) Jianshu Academy of Agricultural Sciences, Nanjing 21001

2) State Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, China

A gene for wide-compatibility (or affinity), which overcomes the partial sterility frequently encountered in the progeny of Indica-Japonica crosses (Ikehashi and Araki 1988), can be used for exploiting heterosis of distant crosses in hybrid rice breeding. In order to facilitate the development of new strains with wide-compatibility and to isolate the gene by map-based cloning, we have attempted to determine the approximate location of a wide-compatibility gene on the RFLP linkage map.

Three rice strains were used as the parents for constructing the mapping population: 02428, a strain that derived the Wc gene from a landrace originating in Yunnan Province; Balilla, a Japonica cultivar from Italy; and Nanjing 11, an Indica cultivar developed in China. These three strains were crossed in the order of 02428/Balilla//Nanjing 11, and screened for restriction fragment length polymorphisms with 11 probes from chromosome 6 on the RFLP linkage map (obtained from Dr. S.D. Tanksley's laboratory in June, 1992), which were likely to be linked to the Wc locus as deduced on the basis of previous results. Three 

Table 1. Linkage between each pair of the five marker loci
===============================================================================
                 Number of plants for each genotype        X2    Recombination
Loci          =====================================   n          value+/-SE
              13/13*  13/23  23/13  23/23
===============================================================================
Wc/C             29      5      2     32              68  43.2   10.3+/-3.7
Wc/Est2          31      3      1     33              68  53.1    5.9+/-2.9
Wc/RG138         26      5      1     30              62  41.0    9.7+/-3.7
Wc/RG213         27      4      1     31              63  45.0    7.9+/-3.4
Wc/RZ398         28      5      3     27              63  35.1   12.7+/-4.2
C/Est2           30      1      2     35              68  56.5    4.4+/-2.5
C/RG138          26      2      1     33              62  50.5    4.8+/-2.7
C/RG213          27      2      1     33              63  51.5    4.8+/-2.7
C/RZ398          25      4      6     28              63  29.4   15.9+/-4.6
Est2/RG138       27      2      0     33              62  54.4    3.2+/-2.2
Est2/RG213       28      2      0     33              63  55.4    3.2+/-2.2
Est2/RZ398       27      3      4     29              63  38.1   11.1+/-4.0
RG138/RG213      26      1      1     34              62  54.1    3.2+/-2.2
RG138/RZ398      24      3      6     29              62  31.2   14.5+/-4.5
RG213/RZ398      25      3      6     29              63  32.1   14.3+/-4.4
==============================================================================
*13/13: genotype of the first locus/genotype of the second locus; 1, 2 and 3
represent alleles from 02428, Balilla and Nanjing II, respectively.

Fig. 1. Map position of the Wc locus for wide affinity in relation to RFLP, isozyme and morphological markers on chromosome 6.

probes (RG138, RG213 and RZ398) detected polymorphisms between 02428 and Balilla and thus should be useful for mapping the Wc gene. In addition, 02428 and Balilla also showed differences in two alleles at an isozyme locus Est-2 and a marker locus conditioning chromogen for anthocyanin (C), and therefore both were found to be linked to the Wc gene (Li et al. 1991). Thus, five segregating marker loci were employed in the mapping.

A total of 68 plants were obtained from the triparent cross; and data for all the five marker loci were collected from each individual. The effect of alleles at the Wc locus was measured by percent seed-setting on bagged panicles and was classified into fertile (>70%) and partly sterile (<70%) groups. The results showed that fertile and partly sterile plants segregated in an 1:1 ratio, confirming that the compatibility in this triparent cross is governed by one major gene locus. All the five marker loci are linked to the Wc gene locus as determined by X2 tests (Table 1). Recombination frequencies for all possible pairs of loci were calculated using the maximum likelihood algorithms (Allard 1956). A linkage map was constructed on the basis of recombination values to illustrate the relative position of the Wc gene on the RFLP linkage map (Fig. 1). It is clear that the relative map position of the Wc gene determined in this study agrees with that reported in previous studies.

References

Allard, R.W., 1956. Formulas and tables to facilitate the calculation of recombination values in heredity. Hilgardia 24: 235-237.

Ikehashi, H. and H. Araki, 1988. Multiple alleles controlling F1 sterility in remote crosses of rice (Oryza sativa). Jpn. J. Breed. 38: 283-291.

Li, H., L. Tang and J. Zhou, 1991. Marker-based analysis of wide compatibility in rice. Hybrid Rice (4): 22-24.