Cytological Characterization of Interspecific Hybrids in Rice (Oryza sativa L.)

The wild species of Oryza are an important source of useful genes for resistance to biotic and abiotic stresses in rice. In this study, wide hybridization was used to widen the genepool of japonica rice cultivars. Interspecific crosses were made between three japonica rice cultivars and four wild species of the genus Oryza. Hybrids were produced normally through crosses between O. sativa (AA genome) and O. rufipogon (AA genome). However, hybrids between O. sativa and other distantly related wild species such as O. officinalis (CC genome), O. minuta (BBCC genome), and O. alta (CCDD genome) were produced following hybridization and embryo rescue. The hybrids were intermediate in their morphological characters, compared with the parents of cultivated and wild species. The hybrids between O. sativa and O. rufipogon were partially sterile but the hybrids between O. sativa and O. officinalis, O. sativa and O. minuta, O. sativa and O. alta were completely sterile. Cytological analysis of the interspecific hybrids, AA x CC, AA x BBCC, AA x CCDD showed irregular meiosis with predominant occurrence of univalents and unequal distribution of chromosomes at anaphase 1 of meiosis. Genomic In-situ Hybridization (GISH) analysis showed the presence of O. minuta chromosomes in the F₁ hybrids between O. sativa and O. minuta cross.