INTERSPECIFIC HYBRIDIZATION OF CULTIVATED RICE, ORYZA-SATIVA L WITH THE WILD-RICE, ORYZA-MINUTA PRESL

Crosses were made between four varieties ('Mahsuri', 'Setanjung', 'MR8 4' and 'MR103') of Oryza sativa L. (2n = 24, AA) and one accession of O. minuta (2n = 48, BBCC). The seed set obtained ranged between 9.5% a nd 25.1% depending on the rice variety used. By rescuing 14-day-old em bryos and culturing them on 25%-strength MS medium we obtained a total of 414 F-1 hybrids. The F(1)s were vigorous, tillered profusely, were perennial and male-sterile. The hybrids were triploid (ABC) with 36 c hromosomes and showed irregular meiosis. The average frequency and ran ge of chromosome associations at metaphase I or early anaphase I polle n mother cells of F-1 plants were 29.31(16-36) Is + 3.32(0-10) IIs + 0 .016(0-1) IIIs + 0.002(0-1) IVs. Upon backcrossing the original triplo id hybrids and colchicine-treated hybrids to their respective recurren t parents, and further embryo rescue, 17 backcross-1 (BC1) plants were obtained. Of all the crosses using MR84, no BC1 plant was obtained ev en after pollinating 13 894 spikelets of the triploid hybrid. The BC(1 )s were similar in appearence to the F(1)s and were male-sterile, thei r chromosome number ranged from 44 to 48. By backcrossing these BC(1)s and nurturing them through embryo rescue, we obtained 32 BC2 plants. Of these, however, only 18 plants grew vigorously. One of these plants has 24 chromosomes and the other 17 have chromosome numbers ranging b etween 30 and 37. The 24-chromosome plant was morphologically similar to the O. sativa parent and was partially fertile with a pollen and sp ikelet fertility of 58.8% and 12.5% respectively. All of the F-1 and B C1 plants were found to be resistant to five Malaysian isolates (X066, XO99, X0100, X0257 and X0319) of Xanthontonas campestris pv oryzae. A mongst the BC(2)s, the reaction varied from resistant to moderately su sceptible. The 24-chromesome BC2 plant was resistant to the four isola tes and moderately resistant to isolate XO100 to which the O. sativa p arent was susceptible.