Centre for Plant Molecular Biology, Department of Genetics, Osmania University, Hyderabad 500007, India
The genus Oryza has two cultivated species and about 18 wild species. The transfer of genes for resistance to biotic stresses from several wild species into cultuvated rice, O. sativa, has been achieved through wide hybridization using embryo rescue technique (Jena and Khush 1990; Multani et al. 1994). The wild perennial grass species Porteresia coarctate Tateoka formerly O. coarctata Roxb. is considered as a potential source of genes for salinity tolerance.
Crosses between four rice cultivars such as IR8, IR28, IR36, Tellahamsa on one hand and P. coarctata on the other were made using rice cultivars as female parents. Spikelets were emasculated before anthesis and pollinated heavily with P. coarctate pollen. The pollinated spikelets were sprayed with GA3 (75 ppm) after 24 hours twice a day for 5 days. On 6th day the spikelets were collected and checked aseptically for embryo development using the method of Jena and Khush (1984). The tiny globular embryos were implanted on quarter strength MS medium and embryo germination was observed after two weeks. The germinated seedlings were slow growing and took two months to reach two leaf stage. Eight hybrids were successfully obtained from a cross between IR36 and P. coarctate whereas two hybrids were from the cross of IR28 and P. coarctate. The crossability ranged from 0.009% to 0.13% (Table 1). The hybrid seedlings were planted in Yoshida's culture solution until maturity. The hybrid plants were of short height (10-12 cm) having short leaves, profuse tillering, small panicles with 10-15 spikelets each and with short awns (Fig. 1). Chromosome counts of the hybrids were made at diakinesis and metaphase-I stages of meiosis and were found to have 36 chromosomes. The hybrids are male sterile and being
Table 1. Seed set and crossability of crosses between cultivated rice (O.
sativa) and P. coarctata
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O. sativa Spikelets Seed set Embryo Hybrid Crossability
(female) pollinated (%) cultured plant (%)
(no.) (no.) (no.)
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IR8 1351 0.51 5 0 0.00
IR28 2160 0.46 4 2 0.09
IR36 5845 0.30 14 8 0.13
Tellahamsa 5615 0.19 5 0 0.00
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multiplied vegetatively for backcrossing with O. sativa as recurrent parents. is the first report of hybrids between rice and P. coarctata.
References
Akbar, M., K. K. Jena and D. V. Seshu, 1987. Salt tolerance in wild rices. inti. Rice Res. Newsl. 15(5): 15.
Jena. K. K. and G. S. Khush, 1984. Embrvo rescue of interspecific hybrids and its scope in rice improvement. Rice Genet. Newsl. 1: 133-134.
Jena, K. K. and G. S. Khush, 199O. Introgression of genes from Oryza officinalis Wall. ex Watt to cultivated rice, O. sativa L. Theor. Appl. Genet. 80: 737-745.
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 introgression of genes from Oryza australiensis Domin. to cultivated rice O. sativa L. Theor. Appl. Genet. 88: 102-109.