• Rgn12

3. Production of hybrids through embryo rescue between tropical japonica rice
        and wild species of Oryza
           Buang Abdullah and Ida H. Somantri
           Biotechnology Research Institute tor Food Crops, CRIFC, Indonesia
 
       The cultivated rice varieties in Indonesia are classified into two groups, namely indicas and tropical japonicas formerly known as javanicas. Improved indica varieties occupy more than 90% of lowland rice areas whereas tropical japonicas are mostly grown under upland and high elevation conditions. Rice breeders in Indonesia have been attempting to improve tropical japonicas. However, not much progress has been made. This is mainly due to high hybrid sterility in the crosses involving tropical japonica varieties. New plant type rices based on tropical japonica germaplasm are being explored as a new frontier for increasing the yield potential of rice. The new plant type lines having few but all productive tillers, large panicles, sturdier stems, deeper root system. thick and dark green leaves, and maturity of 115-120 days have been produced at IRRI. However, resistance to diseases and insects and improved grain quality characteristics need to be incorporated into new plant types before they are used for commercial cultivation (Khush. 1995).

    To widen the gene pool of tropical japonicas (new plant type), wild species offer great potential for incorporating diverse genes for disease and insect resistance. Genes for brown planthopper (BPH) and bacterial blight resistance have already been transferred across crossability barriers from wild species into elite breeding lines of indica rice (Jena and Khush, 1990: Multani et al.. 1994). In this communication, we report the successful production of interspecific hybrids between tropical japonicas and wild species of rice.

    Five tropical japonica varieties having good grain and eating quality were crossed with four wild species of rice having disease and insect resistance. The florets were sprayed with 75 ppm gibberellic acid (GA₃) after emasculation and with a solution of GA₃ indole acetic acid (IAA). and kinetin (Kin) with the concentrations of 100, 25 and 5 ppm, respectively after pollination. After 10-14 days of pollination, hybrid embryos were excised and cultured on 1/4 MS medium in test tubes, following the procedure given by Jena and Khush (1984). The cultures were incubated in a dark room with 26-28°C until germination. One-leaf stage plantlets (seedlings) were then transferred to lighted room. Plantlets having 3 leaves were transferred from agar medium to sterile distilled water in Erlenmeyer flasks to induce more roots. Plantlets with roots were transferred to pots containing sterile soil for 1-2 weeks. Thereafter, plantlets were transferred to bigger pots and placed in the greenhouse. Data on cross-combinations, number of florets pollinated. and embryos cultured are shown in Table 1.

    Following embryo rescue, hybrids were successfully obtained between several tropical japonica varieties and four wild species of 0ryza (Table 1 ). The hybrids showed intermediate characteristics between their parents. Attempts are being made to produce backcross progenies for the transfer of genes from wild species into tropical japonicas.
 
 

References

Jena, K. K. and G. S. Khush, 1984. Embryo rescue of interspecific hybrids and its scope in rice improvement.
        RGN 1:133-134.
Jena, K. K. and G. S. Khush. 1990. Introgression of genes from 0ryza officinalis Wall. ex Watt to cultivated
        rice. 0. sativa L. Theor. Appl. Genet. 80: 737-745.
Khush, G. S. 1995. Modem varieties—their real contribution to food supply. Geo Journal 35(3): 275-284.
Multani, D. S.. K. K. Jena, D. S. Brar. B. G. delos Reyes, E. R. Angeles and G. S. Khush, 1994.
    Development of monosomic alien addition lines and introgreesion of genes from 0ryza aystraliensis
    Domin to cultivated rice 0. sativa L. Theor. Appl. Genet. 88: 102-109.
 
 

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