International Rice Reseach Institute, P.O.Box 933, Manila, Philippines
Wide hybridization in cereals is a significant plant breeding tool
for the incorporation of desirable characters from wild into the cultivated
species. Several accessions of three diploid wild species of rice, e.g., O.
australiensis (Domin), O. officinalis (Wall), and O. brachyantha (Chev. et
Roehr) are resistant to all biotypes of brown planthopper (BPH). In order to
transfer genes for BPH resistance from these wild species we crossed them
with three improved plant-type BPH susceptible lines of Oryza sativa L.,
e.g., IR1529-680-3-2, IR25587-109-3-3-3-3 and IR31917-45-3-2.
We used 3 accessions of O. australiensis, 5 accessions of O. officinalis and 1 accession of O. brachyantha as male parents in crosses with three breeding lines of cultivated rice. Due to cross incompatibility between the parents we obtained very low seed set and few hybrid seeds we obtained, were poorly developed. Most of the hybrid embryos started degenerating two weeks after pollination because of the incompatibility between the genomes.
To overcome the problem of degeneration of interspecific hybrid embryos we resorted to embryo rescue work. Spikelets, after 14 days of pollination, were taken and surface sterilized in sodium hypochlorite solution (35%) supplemented with 2 drops of Twin-20. After washing them in
Table 1. Embryo rescue of interspecific hydrids
============================================================================= Embryos Embryos Percentage Hydric combination cultured germinated of ger- mination ============================================================================= IR1529-680-3-2 x O. australiensis (1) 27 31 77.8 IR1529-680-3-2 x O. australiensis (2) 34 13 38.2 IR1529-680-3-2 x O. australiensis (3) 36 27 75.0 IR1529-680-3-2 x O. officinalis (1) 148 83 56.1 IR1529-680-3-2 x O. officinalis (2) 174 78 44.8 IR1529-680-3-2 x O. officinalis (3) 98 72 73.5 IR1529-680-3-2 x O. officinalis (4) 6 3 50.0 IR1529-680-3-2 x O. officinalis (5) 8 5 62.5 IR1529-680-3-2 x O. brachyantha 37 29 73.5 IR25587-109-3-3-3-3 x O. australiensis (1) 8 4 50.0 IR25587-109-3-3-3-3 x O. australiensis (2) 5 4 80.0 IR25587-109-3-3-3-3 x O. australiensis (3) 7 5 71.4 IR25587-109-3-3-3-3 x O. officinalis (1) 41 21 51.2 IR25587-109-3-3-3-3 x O. officinalis (2) 19 12 63.2 IR25587-109-3-3-3-3 x O. officinalis (3) 45 28 62.2 IR25587-109-3-3-3-3 x O. officinalis (4) 13 6 46.2 IR25587-109-3-3-3-3 x O. officinalis (5) 15 12 80.0 IR31917-45-3-2 x O. australiensis (1) 16 8 50.0 IR31917-45-3-2 x O. australiensis (2) 14 6 42.9 IR31917-45-3-2 x O. australiensis (3) 9 5 55.6 IR31917-45-3-2 x O. officinalis (1) 59 39 66.1 IR31917-45-3-2 x O. officinalis (2) 71 49 69.0 IR31917-45-3-2 x O. officinalis (3) 7 3 42.9 IR31917-45-3-2 x O. officinalis (4) 22 14 63.6 IR31917-45-3-2 x O. officinalis (5) 13 4 30.8 IR31917-45-3-2 x O. brchyantha 5 4 80.0 =============================================================================
The hybrid plants of the three interspecific crosses are now growing. We shall examine their cytological behavior and pollen and seen fertility and study the possibility of gene transfer from these wild species to the cultivated rice.