35. Embryo rescue of interspecific hybrids and its scope in rice improvement


K. K. JENA and G. S. KHUSH

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

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                                             Embryos   Embryos     Percentage
Hydric combination                           cultured  germinated  of ger-
                                                                   mination
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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
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sterilized water, the delicate young embryos were excised and isolated under a stereomicroscope in an asceptic condition on a laminar flow bench. The isolated embryos were cultured asceptically on 1/4 MS medium and were incubated in the dark (25 +\- 1degC) until germination. The seedlings were kept in light incubation room up to three leaf stage and transferred to soil after growing in liquid culture medium for 10 days. The germination of hybrid embryos ranged from 38%-77%, 46%-80% and 31%-80% in the interspecific hybrids of three varieties, respectively (Table 1).

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.