23. Linkage between Pgi-2 and photoperiod sensitivity

M. A. SALAM1, D. J. MACKILL2 and J. C. GLASZMANN3

1) Plant Breeding Division, BRRI, Gazipur 1701, Bangladesh

2) Division of Plant Breeding, Genetics and Biochemistry, IRRI, P. 0. Box 933, Manila, Philippines

3) IRAT-CIRAD, BP5035, 34032 Montpellier cedex, France

It is useful to have a genetic marker to monitor genotypes in populations segregating for photoperiod sensitivity (PS). The isozyme gene Pgi-2 can possibly be used to identify the PS gene (Se-1) since the two are apparently tightly linked (Kinoshita 1986, Oosumi et al. 1989). This study was conducted to determine the feasibility of using the isozyme locus Pgi-2 to identify genotypes with the major PS gene and to estimate the linkage intensity between the two genes. The study was carried out at the International Rice Research Institute (IRRI), Los Banos, Laguna, Philippines situated at 14 deg N.

Table 1. Distribution of flowering date in F2 plants from crosses between photoperiod sensitive and insensitive isogenic pairs, seeded on May 10

======================================================================
                         No. of plants with flowering dates
                ======================================================
Cross    Genera-         August       September      October
         tion   (91)a  ========== =============== ===============Total
                  9 14 19 24 29   3 8 13 18 23 28 3  8 13 18 23 28
======================================================================
IR38697-
6-1-6-3   P1                                               3  5  1   9
    x     F2     18  9  4  3  9   2 7  4 10  2    7 17 15 28  9  3 147
6-1-6-1   P2            4  3  1   1                                 10
IR38699-
53-3-3-2  P1                                               3  3  4  10
          F2                     3 11 10  3       1  3  5 22 22 19  99
53-3-3-1  P2                        5  2  4                         11
======================================================================
a-Days to flower after seeding, 91 days on August 9.
Two F2 populations generated from two single F1 plants of each cross were seeded on 10 May 1987 and transplanted to the screenhouse concrete bed. Horizontal starch gel electrophoresis (Glaszmann et al. 1988) was used to determine the isozyme variants of Pgi-2 alleles 1 and 2 of each progeny. The plants flowering before October were considered photoperiod insensitive and those flowering in October or later were classified as photoperiod sensitive.

There were 14-d and 9-d gaps between the flowering of sensitive and insensitive plants in the F2 Populations (Table 1). This indicated that the sowing on 10 May was appropriate to differentiate the sensitive and insensitive segregants in both crosses. The segregation pattern of 72 sensitive : 27 insensitive progenies (Table 2) in the cross IR38699-53-3-3-2/IR38699-53-3-3-1 showed a good fit to the expected monogenic ratio of 3 sensitive : 1 insensitive while a digenic ratio of 9 sensitive: 7 insensitive was obtained in the cross IR38697-6-1-6-3/IR38697-6-1-6-1. A simple monogenic inheritance pattern was expected in both crosses because they involved members of a pair of sensitive and insensitive isogenic lines. The digenic ratio in the latter could be explained by a dominant PS gene interacting with a recessive inhibitor carried by the insensitive line IR38697-6-1-6-1. These results were also observed by Chang et al. (1969).

The isozyme assay was done both at seedling and tillering stages in each cross and the isozyme patterns were found to be the same. The highly significant differences from independence for the distribution of Pgi-2 alleles and sensitivity to photoperiod in both crosses implied a close association of Pgi-2 and PS (Table 2). This finding confirmed the preliminary work of Poonyarit et al. (1987, 1989) who showed that the allele Pgi-21 was associated with late (sensitive) F3 lines of sensitive/insensitive crosses.

The linkage intensity was estimated in the cross IR38699-53-3-3-2/IR38699-53-3-3-1 by the maximum likelihood method described by Allard (1956). The

Table 2. F2 segregation of photoperiod sensitivity gene(s) and an isozyme gene (Pgi-2) in two crosses

====================================================================
                 No.of segregants for each     Test of Significance
Cross            allele of isozyme locus Pgi-2
                 ============================= =====================
                 Sensitivity 1/1 1/2 2/2 Total Designation      X2  
====================================================================
IR38699-53-3-3-2 Sensitive    21  43   8    72 Sensitivity(3:1) 0.17
          x      Insensitive   3   8  16    27 Pgi-2 locus(1:2:1)0.09
IR38699-53-3-3-1
                 Total        24  51  24    99 Independence of Pgi-2 24.85**
                                               and sensitivity
IR38697-6-1-6-3  Sensitive    17  56   6    79 Sensitivity(9:7) 0.29
          x      Insensitive   7  32  29    68 Pgi-2 locus(1:2:1) 7.37*
IR38697-6-1-6-1
                 Total        24  88  35   147 Independence of Pgi-2 21.68**
                                               and sensitivity
====================================================================
* Significant at 5% level.
** Significant at 1% level.
estimated recombination value between Pgi-2 and PS was 23.2+/-4.7. This moderate linkage was also observed by Vergara et al. (1988) in deepwater rice crosses. if these cultivars possess Se-1, then Pgi-2 may not be tightly linked to this gene as previously reported. Alternately, perhaps the PS gene in these cultivars is different from that present in cultivars studied in Japan.

References

Allard, R. W., 1956. Formulas and tables to facilitate the calculation of recombination values in heredity. Hilgardia 24: 235-278.

Chang, T. T., C. C. Li and B. S. Vergara, 1969. Component analysis from seeding to heading in rice by the basic vegetative phase and photoperiod sensitive phase. Euphytica 18: 79-91.

Glaszmann, J. C., B. G. de los Reyes and G. S. Khush, 1988. Electrophoretic variation of isozymes in plumules of rice (Oryza sativa L.)-A key to identification of 76 alleles at 24 loci. IRRI Res. Paper Series No. 134.

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

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.

Poonvarit, M. D.J. Mackill and B. S. Vergara, 1987. Two genes affecting photoperiod sensitivity in rice. RGN 4: 87-89.

____, ____ and ____, 1989. Genetics of photoperiod sensitivity and critical daylength in rice. Crop Sci. 29: 647-652.

Vergara, G. V., N. L. Manigbas, J. C. Glaszmann and D. Hille Ris Lambers, 1988. Linkage analysis between photoperiod sensitivity and isozyme markers in deepwater rice. Philipp. J. Crop Sci. 13 (Suppl. 1): S42.