10. Interspecific hybrids produced through embryo rescue between cultivated and eight wild species of rice

D. S. BRAR, Ruth ELLORAN and G. S. KHUSH

International Rice Research Institute, P.O. Box 933, Manila, Philippines

The genus Oryza to which cultivated rice (Oryza sativa L.) belongs has more than 20 wild species. These wild species are an important reservoir of useful genes for resistance to major diseases and insect pests and tolerance to abiotic stresses. To widen the rice gene pool and for transfer of useful alien genes, we have produced hybrids of rice varieties with eight wild species (Table 1). In these cross-combinations, 15977 rice florets were pollinated with pollen of eight species and 1420 seeds were obtained. The seed set ranged from 3.8 to 22.1 percent average being 8.9 percent. From crosses of rice with 12 accessions of wild species, 204 hybrid plants were produced through embryo rescue. These hybrids were produced specifically to transfer genes for tungro tolerance from O. officinalis (105220) and O. latifolia (105141, 105142); yellow stemborer and tungro tolerance from O. ridleyi (100821); brown planthopper and bacterial leaf blight resistance from O. rhizomatis and O. eichingeri; high biomass from O. alta and to determine genomic constitution of O. ridleyi, O. granulata and O. indandamanica.

Immature embryos, 10-14 day of post pollination were excised from different cross-combinations. These embryos were cultured on 1/4 MS medium and were incubated in the dark (25±1°C) until germination following the procedure of Jena and Khush (1984). The seedlings were kept in the light incubated room up to three leaf stage and transferred to soil after growing in liquid culture medium for 10 days. The hybrid nature of some of these plants was confirmed from PMC analysis. In general, the hybrids were intermediate in morphological characters between the two parents (Fig. 1). The F1 hybrids were male sterile. These hybrids are being maintained and multiplied through tiller propagation. We have already produced BC1 plants through embryo rescue from crosses of IR42 X O. eichingeri, IR31917-45-3-2 X O. rhizomatis and IR31917-45-3-2 X O. granulata. We now have interspecific hybrids involving elite breeding line/varieties of rice with 12 wild species having genomes other than A.

Table 1. Interspecific hybrids produced through embryo rescue between
cultivated rice (O.  sativa) and eight wild species of Oryza
===============================================================================
              Hybrid-combination
=============================================
              Wild species (male)
          ===================================
O.sativa      Species    Genome   Accession    Florets  Seed set Embryos Hybrid
(female)                                     pollinated  (No.)  cultured plants
                                                (No.)             (No.)   (No.)
===============================================================================
IR42      O. eichingeri    CC      105181        48       20       18      13
IR64(4n)        "          "       105181        12        6        1       1
IR31917-45-3-2  "          "       101422       184       33        5       1
IR54            "          "       101422       112       12        0       0
IR64            "          "       101422       106       12        4       1
IR64(4n)        "          "       101430        55        5        4       4
IR20     O. officinalis    CC      105220        90       30        6       1
IR22            "          "       105220       238        2        0       0
IR24            "          "       105220       416        6        0       0
IR31917-45-3-2  "          "       105220       452       10        1       0
IR70            "          "       100878       105        1        1       1
IR31917-45-3-2 O.rhizomatis CC     105432       127       26       19       8
IR36(4n)        "          "       105432       609        2        0       0
IR20     O. latifolia     CCDD     105141       441       64       39      25
IR22            "          "       105141       786      185       44      33
IR24            "          "       105141      1264      173       79      36
IR31917-45-3-2  "          "       105141      1745      131       49       6
IR64(4n)        "          "       105141       122        2        0       0
IR20            "          "       105142       384       32        8       6
IR22            "          "       105142       294       27        5       2
IR24            "          "       105142       932       40       19      15
IR31917-45-3-2  "          "       105142       407       37       17      13
IR36(4n)        "          "       105142       103       11        8       0
IR31917-45-3-2 O.alta     CCDD     101395       111       63        0       0
IR64            "          "       101395        54       18        3       2
IR64(4n)        "          "       101395        80        0        0       0
IR36(4n)        "          "       101395       121        0        0       0
IR72     O. ridleyi      unknown   100821      1263        3        1       1
IR74            "          "       100821      2091      224       40      27
IR31917-45-3-2  "          "       100821      1259      128       12       1
IR56     O. granulata    unknown   100879       372       42        2       0
IR31917-45-3-2  "          "       100879       537       45       14       3
IR36(4n)        "          "       100879       642        3        0       0
IR31917-45-3-2 O.indandamanica unknown  -       160        1        0       0
IR36(4n)        "          "                     95        0        0       0
IR64(4n)        "          "                    160       26        4       4
===============================================================================

Fig. 1. Morphology of O. sativa cv. IR 31917-45-3-2 and (left), F1 hybrid (center) O. granulata(right).

 

Reference

Jena, K. K. and G. S. Khush, 1984. Embryo rescue of interspecific hybrids and its scope in rice improvement. RGN 1: 133-134.