Development and identification of synthetic interspecific hybrids between Oryza sativa and Oryza australiensis

Oryza sativa and Oryza australiensis are both diploid and containing AA and EE genomes, respectively. Although their distant genetic relationship makes crossing difficult, interspecific hybrids between the two species were obtained by young embryo rescue in this study. The F1 hybrids resembled the wild rice parent, O. australiensis, in respect of morphological traits such as plant height, lengths and widths of flags and second leaves, panicle type and length, long-awned spikelets, grain shattering, sensitivity to photoperiod and tillering capability. The genomic components and chromosome pairing of the hybrids were subsequently investigated using a genomic in situ hybridization analysis. Based on the mitotic metaphase chromosomal numbers in the root tips, all these hybrids are characterized to be allodiploids with 24 chromosomes, and their genomic constitution is AE. A poor chromosomal pairing was identified in meiotic anaphase I of the hybrid pollen mother cell as most of the chromosomes were univalent. This work laid the foundation for transferring favorable traits and useful genes from O. australiensis to cultivated rice in the near future.