39. Allelism test for restorer genes of six promising IR restorer lines

K. Govinda Raj and S.S. Virmani

IRRI, PO Box 933, Manila, Philippines


Improved indica rice varieties and breeding lines have reasonably high frequency (20%) of restorer parents for CMS lines possessing "WA" system. The fertility restoration ability of 'WA' cytosterility system has been found to be governed by two independent and dominant genes, one of the genes being stronger in action than the other (Tiangli et al. 1983; Young and Virmani 1984; Virmani et al. 1986; IRRI 1986; IRRI 1986; Govinda Raj and Virmani, unpubl.). We report here results from allelic tests of six promising IR restorer lines viz., IR 26, IR 36, IR 42, IR 54, IR 9761-19-1 and IR 2797-10-2-233.

The allelism tests were conducted by crossing the six restorers in all possible combinations and test crossing the F\1\'s to a CMS line (V 20 A) possessing 'WA' type cytoplasm. The testcross F\1\ progenies were scored for their pollen and spikelet fertility. The presence or absence of partially sterile (PS) and completely sterile (CS) plants in the testcross F\1\ progenies was used as an indication of allelic relationships of restorer genes in the restorer parents involved in the cross combination.

The allelic situation for restorer genes differed in the restorer lines studied (Table 1). Testcross of the F\1\'s IR 26/IR 36 and IR 9761-19-1/IR 53 did not yield any sterile plants in the progeny, indicating that IR 26 and IR 36, and IR 9761-19-1 and IR 54 possess indentical restorer genes between them. However, it appears that IR 42 and IR 2797-105-2-2-3 possess different restorer genes as indicated by the appearance of PS and CS plants in the testcross F\1\ progenies involving these varieties and other restorers. Thus, these four groups of restorers viz., IR 26/IR 36, IR 9761-19-1/IR 54, IR 42 and IR 2797-105-2-2-3 possess different pairs of restorer genes. An appropriate combination of two of the eight restorer genes seems to restore full fertility in F\1\ hybrids with CMS line. The existence of such high number of diverse restorer genes also explains the high (20%) frequency of restorer lines among the elite indica breeding lines. Screening and further genetical analysis of the parental lines involved in the pedigree of these six restorers should enable us to determine precisely the number of diverse restorer genes present and to identify the original source of each of the restorer genes.


Table 1. Segregation pattern in testcross F\1\ progenies (CMS V20A//(Restorer/Restorer) for spikelet fertility

=============================================================================
Testcross progenies           Total No.           Plants (No.) with spikelet
involving restorer/           of plants            fertility reaction*
  restorer F\1\               observed       ================================
                                               F       PF       PS       S
=============================================================================
IR26/IR2797-105-2-2-3           63            54        5        -       4
IR26/IR36                       68            68        -        -       -
IR26/IR42                      135           124        6        -       5
IR26/IR9761-19-1                73            68        3        1       1
IR26/IR54                       90            87        2        -       1
 
IR2797-105-2-2-3/IR36           80            76        1        -       3
IR2797-105-2-2-3/IR42           84            52       14       14       4
IR2797-105-2-2-3/IR9761-19-1    49            40        -        -       9
IR2797-105-2-2-3/IR54           79            69        9        -       1

IR36/IR42                       90            81        1        -       8
IR36/IR9761-19-1                82            77        1        -       4
IR36/54                         94            91        1        -       2

IR42/IR9761-19-1                64            60        1        -       3
IR42/IR54                       76            64       11        -       1

IR9761-19-1/IR54               175           172        3        -       -
=============================================================================
* F (fertile) = 80-100%; PF (partially fertile) = 30-80%; PS (partially sterile) = 1-30%; S (sterile) = 0.



References

International Rice Research Institute, 1986. Annual Report for 1985. Int. Rice Res. Inst., PO Box 933, Manila, Philippines.

Tiangli, Z., S. Jinhua and Y.F. Chu, 1983. A genetical analysis on the fertility of Shan type hybrid rice with wild rice cytoplasm (in Chinese with English summary). Acta Agronomica Sinica 9(4):241-247.

Virmani, S.S., K. Govinda Raj, C. Casal, R.D. Dalmacio and P.A. Aurin, 1986. Current knowledge of an ourlook on cytoplasmic male sterility and fertility rstoration in rice. In Rice Genetics. Int. Rice Res. Inst., PO Box 933, Manila, Philippines. p. 633-647.

Young, J. and S.S. Virmani, 1984. Inheritance of fertility restoration in a rice cross. RGN 1: 102-103.