The genus Oryza has two cultivated and 22 wild species with 2n=24
or 48 chromosomes. Of the two cultivated species, O. sativa (2n=24,
AA) is grown worldwide whereas O. glaberrima (2n=24, AA) is grown
in a limited area in West Africa. O. glaberrima is low yielding
but has useful genes for resistance to rice yellow mottle virus, African
gall midge, nematodes and good level of tolerance to abiotic stresses
such as drought, iron and
aluminum toxicity and phosphorous deficiency.
It is also an important source of weed competitiveness. We are trying
to combine the high productivity of O. sativa with tolerance to
abiotic stresses of O. glaberrima. The two species show strong
reproductive barriers and their F1 hybrids exhibit high level
of sterility (Sano et al. 1979). Several sterility genes differentiate
these two species (Oka 1988). Anther culture is being explored to overcome
sterility in such crosses and to produce homozygous lines, fix recombinants
and use such doubled haploid (DH) lines as mapping populations.
We cultured anthers on N6 medium of 75 F1s from crosses of
10 varieties of O. sativa with 18 accessions of O. glaberrima.
The calli were transferred to MS medium supplemented with 1 mg/l each
of BAP, kinetin and NAA. After 3 to 4 weeks, regenerated shoots were transferred
to 1/4 MS medium devoid of any auxin. After 2-3 weeks, the seedlings with
well developed roots were transplanted in soil. In general, the callus
induction frequency was low and ranged from 0.0-18.6%. Upon culture of
45,400 anthers from 75 F1s; we did not obtain any calli from
34 crosses. The other 41 F1s showed on an average 1.3% callus
formation from 144, 160 cultured anthers.
The plant regeneration ranged from 0.0 to 77.0%. The anther derived calli
from 16 F1s did not show any plant regeneration while in the
remaining 25 F1s, callus induction and plant regeneration varied
among genotypes (Table 1). We have produced 562 DH lines and then characterized
based on plant morphology. However, we obtained 137, 138 and 65 plants
respectively, from three crosses e.g. IR68552-5-3-2 x TOG 6589, IR68037-AC-24-1
x CG14. Others produced less than 30 plants each (Table 1). Among O.
sativa lines, an elite breeding line of new plant type (NPT), IR68552-55-3-2
was found to respond better for producing green plants in crosses with
O. glaberrima. Similarly, O. glaberrima accession, CG14
in crosses with some of O. sativa parents responded favourably
to anther culture. The DH lines showed very high seed sterility, 56.2
The results indicate strong genotypic differences for anther culturability
both for callus induction and plant regeneration. Furthermore, callus
induction and plant regeneration from anther culture were found to be
independent of each other (Table 1). As an example, in the cross IR68552-5-3-2
x TOG 6589, 6.2% anthers formed callus and showed 77.0% plant regeneration
whereas in IR68703-AC-24-1 x CG14, 18.6% anthers underwent callus formation
but showed only 34.4% plant regeneration. High sterility of DH lines is
indicative of presence of several loci for sterility differentiating the
Asian and African rice species.
Jones, M.P., M. Dingkuhn, G.K. Aluko and M. Semon, 1997. Interspecific
Oryza sativa L. x O. glaberrima Steud. progenies in upland
rice improvement. Euphytica 92: 237-246.
Oka, H.I., 1988. Origin of cultivated rice. Developments in Crop Science
Vol. 14, Japan Scientific Society Press Tokyo and Elsevier, Amsterdam.
Sano, Y., Y.E. Chu and H.I. Oka, 1979. Genetic studies of speciation in
cultivated rice: genetic analysis for F1 sterility between
O. sativa and O. glaberrima Steud. Jpn. J. Genet. 54: