L. A. SITCH, R. DALMACIO, D. S. BRAR and G. S. KHUSH
International Rice Research Institute, P.O. Box 933, Manila, Philippines
The genus Oryza to which the cultivated rice (Oryza sativa L.), belongs has more than 20 wild species. These wild species have 2n=24 or 48 chromosomes and represent 6 genomes; AA, BB, BBCC, CC, CCDD, EE, FF. The genomic constitution of some species such as O. granulata, O. meyeriana, O. indandamanica, O. ridleyi and O. longigiumis is unknown. Both O. ridleyi and O. longiglumis are tetraploid species (2n=48). O. longiglumis is distributed along the Koembe River, Irian Java, Indonesia and in Papua New Guinea whereas O. ridleji grows across Southeast Asia and as far east as Papua New Guinea.
Fig. 1. Morphology of O. longiglumis (left), F1 hybrid (center) and O. ridleyi (right).
We have produced F1 hybrid between O. longiglumis (Acc. 100974) and O. ridleyi (Acc. 101453) following embryo rescue. Both O. ridleyi and O. longiglumis are similar in certain morphological characters such as node, stigma and pericarp colour. However colour of basal leaf sheath and awns of O. ridleyi is different from O. longiglumis. The hybrid was intermediate in morphological characters (Fig. 1), and showed expression of dominant traits such as purple leaf sheath and pigmented awns. Meiotic analysis of O. longiglumis showed 61.5% of the cells with 24II, 30.9% with 16-23II+2-16I and 5.2% cells with a ring of four chromosomes. Similar behavior was observed in O. ridleyi (Table 1). The presence of a ring of four chromosomes indicates chromosomal interchange between the two genomes or partial homology between two pairs of chromosomes in the parents. The F1 hybrid showed predominantly 24II (74.2% cells) and one or two rings of four chromosomes in 3.7 and 3.3% cells respectively. The presence of two rings of four chromosomes in the hybrid indicates that the chromosomes involved in interchange/genomic homology are different in the two parents.
The occurrence of 24II in the hybrid shows that the genomes of O. ridleyi and O. longiglumis are identical. Crosses of O. ridleyi with O. sativa, O. minuta and O. officinalis indicate that O. ridleyi genome is different from A, B, and C genomes (Katayama and Onizuka 1979, Katayama et al. 1981). We have made additional crosses with other species to determine the genomic constitution of O. ridleyi and O. longiglumis.
Table 1. Meiotic chromosome configurations in O. longiglumis, O. ridleyi and O. longiglumis x O. ridleyi hybrid ============================================================================== Chromosome No. of cells with chromosome Species/ number 24II configurations Total cells F1 hybrid (2n) ============================= II+I III+I 1IV 21V ============================================================================== O. longiglumis 48 60(61.5) 30(30.9) 2(2.1) 5(5.2) O(O) 97 O. ridleyi 48 62(50.0) 57(46.0) O(O) 5(4.0) O(O) 124 O. longiglumis x 48 141(74.2) 36(17.4) O(O) 7(3.7) 6(3.3) 190 O. ridleyi (F1) ============================================================================== Figures in parenthesis are percent of cells.
Katayama, T. and W. Onizuka, 1979. Intersectional F1 plants from Oryza sativa x O. ridleyi and O. sativa x O. meyeriana. Jpn. J. Genet. 54: 43-36.
Katayama, T., W. Onizuka and Y. B. Shin, 1981. Intersectional F1 hybrids obtained from the crosses Oryza minuta Pres. x O. ridleyi Hook and O. officinalis Wall x O. ridleyi Hook. Jpn. J. Genet. 56:67-71.