12. Linkage relations between the photoperiod sensitivity gene Se-1 and two other genes, Pi-zt and Pgi-2

Atsushi FUKUCHI1, Yukari SUZUKI1, Hirohiko HIROCHIKA2 and Fumio KIKUCHI3

1) Agricultural Research Laboratories, Takeda Chemical Industries, Ltd., Tsukuba, lbaraki, 300-42 Japan

2) Department of Molecular Biology, National Institute of Aerobiological Resources, Tsukuba, 305 Japan

3) Institute of Agriculture and Forestry, University of Tsukuba, Tsukuba, 305 Japan

A photoperiod sensitivity gene (Se-1), an isozyme gene (Pgi-2) and a blast resistance gene (Pi-zt) in rice are located on chromosome 6. Se-1 (or Lm) was found to be closely linked with Pi-zt with the recombination value of 3.5% (Yokoo and Fujimaki 1971). The linkage relations between Se-1 and Pgi-2 or Pi-zt and Pai-2 are inconsistent (Oosumi et al. 1989; Salam et al. 1990; Mackill et al. 1990). In order to determine the linkage relations of the three genes, we used near-isogenic lines (NILs), ES and LR, developed by Yokoo et al. (1980). The ES and LR have the different alleles at three loci. That is, LR has Se-1u, Pgi-22 and Pi-zt, while ES has Se-1e, Pgi-21 and +.

Linkage analysis was carried out by studying, the F2 population from a cross between LR and ES. The distribution of heading date in the F2 showed clear trimodal distribution and fitted well to the segregation ratio of 1 : 2: 1 (early: medium: late) (Fig. 1). The isozyme analysis was carried out according to the procedure described by Oosumi et al. (1989). The F3 progenies were tested for resistant to the blast fungus strain Ken 53-33 by spray inoculation method and the genotypes for resistance of F2 plants were estimated. The segregation of the genotypes for three loci in the F2 are shown in Table 1. They agreed with the


Fig. 1. Frequency distribution of days to heading in the F2 populations of a cross between LR and ES. ____/____ indicates mean and range of parents and F1.


Fig. 2. Relative positions of Se-1, Pgi-2 and Pi-zt on chromosome 6.

segregation ratio of 1: 2: 1.

Cosegregation data among three loci are summarized in Table 2. Recombination values were computed using the MAPL program of Ukai et al. (1991). The recombination values between Se-1 and Pi-zt, Se-1 and Pgi-2, and Pi-zt and Pgi-2 were esti mated to be 1.5+/-0.6%, 5.3+/-1.1% and 6.5+/-1.2%, respectively (Table 2). The linkage values between Se-1 and Pgi-2 are not so tight as described by Kinoshita (1986) and Oosumi et al. (1989).

Fig. 2 shows the relative position of the three genes.

The authors are indebted to Dr. R. Ohsawa for calculating recombination value by their MAPL program.

References

Kinoshita, T., 1986. Standardization of gene symbols and linkage maps in rice. In Rice Genetics, p. 215-228. International Rice Research Institute, Manila, Philippines.

Mackill, D. J., Z. Y. Wang and S. D. Tanksley, 1990. Linkage between a RFLP probe and photoperiod sensitivity. RGN. 7: 145-147.

Oosumi, T., A. Miyazaki, H. Uchimiya, F. Kikuchi and M. Yokoo, 1989. Analysis of glucose phosphate isomerase in near-isogenic lines, and cultivars of rice (Oryza sativa L.). Bot. Mag. Tokyo 102: 283-289.

Salam, M. A., D. J. Mackill and J. C. Glaszmann, 1990. Linkage between Pgi-2 and photoperiod sensitivity. RGN 7: 130-132. 

Table 1. Segregation of the three genes in the F2 population of LR/ES
===============================================================================
Locus  Segregation                            total     X2       P
      =================================                (1:2:1)
      ES type  Hetero type  LR type 
===============================================================================
Se-1    57         125         49             231       2.12  0.50>P>0.25  
Pgi-2   53         125         53             231       1.56  0.50>P>0.25
Pi-zt   58         123         49             230       1.82  0.50>P>0.25
===============================================================================


Table 2. Cosegregation among Se-1, Pgi-2 and Pi-zt in the F2 of LR?ES
===============================================================================
Gene pair     Segregation in the F2 population           X2  (1:2:1:2: Recomb.
A/B        =============================================    4:2:1:2:1) value(%)
           AABB AABb AAbb AaBB AaBb Aabb aaBB aaBb aabb Tot.
===============================================================================
Se-1/Pgi-2   50   7    0    3    113  9    0    5   44  231 303.0***  5.3+/-1.1
Se-1/Pi-zt   56   1    0    1    121  2    1    1   47  230 396.8***  1.5+/-0.6
Pgi-2/Pi-zt  49   4    0    8    110  6    1    9   43  230 283.0***  6.5+/-1.2
===============================================================================
*****: significant at 0.1% level.
Ukai, Y., R. Ohsawa and A. Saito, 1991. MAPL: A package of programs for RFLP linkage mapping. RGN 8: 155-158.

Yokoo, M. and H. Fujimaki, 1971. Tight linkage of blast-resistance gene with late maturity observed in different Indica varieties of rice. Jpn. J. Breed. 21: 35-39.

Yokoo, M., F. Kikuchi, A. Nakane and H. Fujimaki, 1980. Genetical analysis of heading time by aid of close linkage with blast resistance in rice. Bull. Nat. Inst. Agr. Sci. D 31: 95-126. (Japanese/English)