11. Genomic relationship of Oryza longiglumis and O. ridleyi

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+2-161 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. 

       
Table 1.  Meiotic chromosome configurations in O. longiglumis, O. ridleyi and
O.  longiglumis x O. ridleyi hybrid
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                  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.
The occurrence of 2411 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.

References

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.