Fourteen rice accessions resistant to bacterial leaf blight (BB),
caused by Xanthomonas oryzae
pv. oryza (Xoo) and belonging to nine wild Oryza species
representing three genomic groups: AA
(O. nivara, O. barthii, O. longistaminata,
O. rufipogon and O. meridionalis), BBCC (O. punctata,
O. malampuzhaensis and O. minuta) and CCDD (O. latifolia)
were used to produce hybrids with two
O. sativa (2n=24, AA) cultivars PR 106 and Pusa
Basmati 1 (PB 1). The seed set in similar genome
crosses ranged between 1·4 and 79% depending upon the
rice cultivar used. In general, PR 106
showed better crossability with the wild species. Hybrids were obtained
from intergenomic crosses
with O. malampuzhaensis, O. latifolia and O.
punctata, using embryo rescue. Morphologically, the
hybrids were more vigorous than their parents and tended to resemble their
male parent.
Intragenomic hybrids showed little fertility (0·24–8·04%),
while the intergenomic hybrids were
completely sterile. Meiotic studies revealed irregularities in cell
division, with a high frequency of
univalents (12·17–18·75), fewer bivalents
(2·43–5·80) and occasional multivalents, in intragenomic
hybrids. The intergenomic hybrids were characterized by a very high frequency
of univalents
(34·98–35·35). The reaction of the hybrids to
BB revealed the presence of both dominant and recessive
genes in the wild gene pool. The hybrids with O. longistaminata,
O. punctata, O. latifolia and
O. malampuzhaensis showed resistance in the F1
generation, and hence they were likely to carry
dominant genes for resistance, while the hybrids with O. barthii,
O. nivara, O. meridionalis and
O. rufipogon were susceptible and hence carried recessive genes
for resistance.