36. A rapid method for identifying different dwarfing genes in rice


Ish KUMAR1 and T. H. SINGH

Department of Plant Breeding, Puniab Agricultural University, Ludhiana, Punjab, 141004 India

1. Present address: Post Doc. Fellow, Department of Plant Breeding, International Rice Research Institute, P.O. Box 933, Manila, Philippines.


A breakthrough in rice production has been attained through the development of semi-dwarf varieties. The semi-dwarf varieties in addition to having lodging resistance, have high nitrogen responsiveness. TN1 from Taiwan and IR8 from IRRI, Philippines, inherited their common recessive dwarfing gene from Dee-geo-woo-gen (DGWG). After the success of IR8 the breeders depended heavily on this source of short stature. This has resulted in narrow germplasm base of the world's rice crop, as far as dwarfing gene is concerned. Studies are underway for identifying new dwarfing genes. Allele tests between the new genes and the DGWG gene require 3-4 growing seasons as crosses must be made and F\1\ and F\2\ Populations must be examined for plant stature. In this study a new approach to identify a dwarfing gene different from DGWG is reported.

Variety IR8, PR106, TN1, Basmati 370 and IR127-80-10-1 were planted in a single row in rice experimental area, Punjab Agricultural University, Ludhiana (India) in the later part of the rice planting season, i.e., on 15th July, 1982 in two replication. The row to row and plant to plant distance was 30 x 20 cm, respectively. Freshly prepared 100 ppm, solution of GA\3\ was sprayed on five plants of each variety, in each replication, at the booting stage. Final observations on culm elongation after GA\3\ Spray were taken at full maturity of all the varieties. The results with respect to control and sprayed plants are given in Table. 1.

The data show that three varieties, e.g., IR8, TN1 and PR1O6, which have the same dwarfing gene from DGWG, responded similarly to the exogenous supply of GA\3\. All these varieties showed a response of about 30 percent increase in culm elongation over their respective controls. Even the traditional tall variety Basmati 370 indicated a response of 14 percent increase in plant height. On the other hand plant height of IR127-80-10-1 at maturity showed no increase after the exogenous GA3 spray (Table 1). This lack of response to GA\3\ clearly shows that the dwarfing gene in IR127-80-10-1 is different from the DGWG gene present in other three dwarf varieties.

The dwarfing gene of IR127-80-10-1 ws found to be different from DGWG dwarfing gene by genetic analysis. The height of F\1\ plants of the cross between TN1 and IR127-80-10-1 was 135 cm and compared to 83 cm and 94 cm for TN1 and I127-80-10-1, respectively. The F\2\ of this cross showed transgressive segregation, the range being 60 cm to 165 cm. IRRI (1967) also reported that the dwarfing gene in CP-SLO (one of the parents of IR127) was different from the DGWG gene.


Table 1. Plant height of different varieties before and after GA3 application

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                 Plant height (cm)

Variety                               Percent increase in
                 Treated  Control     height over control
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IR8                 86       65            32
TN1                 88       70            26
PR106               88       68            30
Basmati 370        190      166            14
IR127-80-10-1       76       75             1
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These results indicate that GA3 responsive and non-responsive dwarf plants can be identified easily in the segregating populations of the crosses between varieties having CP-SLO gene and the DGWG gene. All the plants having least response to GA3 would be having a dwarfing gene from CP-SLO and the ones having DGWG would respond to GA3 application. Such an approach in rapidly identifying the different dwarfing genes can be extended to other dwarfing sources in rice also.


Reference

IRRI, 1967. International Rice Reseach Institute, Annual Report for 1966.