8. Cytogenetic and molecular characterization of
an intergeneric hybrid between Oryza sativa L. and Porteresia
coarctata (Roxb.) Tateoka
D.S. brar, R.M. elloran, J.D. talag, F. abbasi
and G.S. khuch
International Rice Research Institute. P.O. Box 933, 1099 Manila,
Philippines
The genus Oryza has two cultivated species and 22
wild species. A number of genes for resistance to biotic stresses have
been transferred from wild species into the cultivated rice through embryo
rescue and backcrossing procedures (Brar and Khush 1997). The wild perennial
grass species Porteresia coarctata Tateoka (formerly 0. coarctata
Roxb., 2n = 48) is considered as a potential source of genes for salinity
tolerance.
We report the successful production of intergeneric hybrid
(O. sativa x P. coarctata) through embryo rescue.
Panicles of 0. sativa cv. IR56 were emasculated and pollinated with
pollen of P. coarctata. Immature embryos after 10-14 days of pollinations
were excised and cultured on the nutrient medium to obtain the hybrid seedling.
Isozyme analysis was used to characterize the F1 hybrid. Meiotic
chromosome analysis was carried out from anthers squashed in 2% acetocarmine.
Total genomic DNA of O. sativa and P. coarctata was
individually used as a probe. EcoRI digested DNA from both the species
was used in DNA hybridization to determine the molecular divergence and
nature of the F1 hybrid.
The hybrid is slow growing and is intermediate in morphological
characteristics (Fig. 1 ). It is completely male sterile. Jena (1994) also
reported a hybrid between (O. sativa and P. coarctata.
Starch gel electrophoresis showed IR56 and P. coarctata to be highly
polymorphic. Out of 20 loci, Amp1, Amp2, Amp3, Amp4, Pgi1, Pgi2, Pgd1,
Pgd2, Adhl, Sdhl, Mal1, Got1, Got3, Mdh1, Mdh2, Mdh3, Est1, Est2, Est5,
Est9 examined, 16 were polymorphic. The F1 showed isozyme
bands from both parents indicating hybrid nature. Meiotic chromosome analysis
of the hybrid showed 36 univalents at metaphase I indicating lack of pairing
between chromosomes of O. sativa and P. coarctata
(Fig. 2).
Hybridization of P. coarctata DNA when used as
a probe showed strong hybridization with P. coarctata and limited
cross hybridization with IR56 indicating strong diver-
44 Rice Genetics Newsletter Vol. 14
Figs. 1-3: 1. Intergeneric hybrid between 0ryza sativa
(2n = 24) and Porteresia coarctata (2n = 48) produced
through embryo rescue: 2. Meiotic metaphase showing 36 univalents in the
F1 hybrid indicating lack of homoeology between chromosomes
of 0. sativa and P. coarctata; 3. Hybridization after probing
with genomic DNA of P. coarctata (A) and IR56 (B). Lane 1-molecular
marker, 2-0. sativa cv. IR56; 3- F1 hybrid; 4-P. coarctata.
(A) showing strong hybridization signal after probing with genomic DNA
of P. coarctata (lane 4) and very low cross hybridization with DNA
of IR56 (lane 2). B-strong hybridization signal after probing with DNA
of IR56 (lane 2) and limited hybridization with DNA of P. coarctata
(lane 4).
gence between the genomes of O. sativa and
P. coarctata (Fig. 3). Similar divergence was observed when IR56
DNA was used as a probe. Total genomic DNA hybridization approach has been
used to determine divergence between various species of Oryza (Aggarwal
et al. 1997). Cytogenetic and molecular analysis confirmed true
hybrid nature of the Fi and showed limited homoeology between (9. sativa
and P. coarctata ge-
nomes.
We have vegetatively multiplied the F1 hybrid.
These hybrid plants are being used in backcrossing with IR56 for the transfer
of genes for salinity tolerance from P. coarctata into rice.
References
Aggarwal, R.K., D.S. Brar and G.S. Khush, 1997. Two
new genomes in the Oryza complex, identified on the basis of molecular
divergence analysis using total genomic DNA hybridization. Mol. Gen. Genet.
254:1-12.
Brar, D.S. and G.S. Khush, 1997. Alien introgression in rice.
Plant Molecular Biology 35: 35-47. Jena, K.K., 1994. Development
of intergeneric hybrid between 0. sativa and P. coarctata.
RGN II: 78-79.