The Cytogenetics of F₁ Hybrids from Oryza nivara Sharma et Shastry×O. sativa L.

Abstract

IRRI Accession 101508 of the wild species Oryza nivara Sharma et Shastry was crossed directly and reciprocally to six varieties of the cultivated species, O. sativa L. This accession was cross-compatible with the six O. sativa cultivars.
Each of the parents and hybrids have median, submedian, and subtelocentric chromosomes. A combination of three median (chromosome number 2, 3 and 7), seven submedian (number 1, 4, 5, 8, 9, 11 and 12), and two subtelocentric chromosomes (number 6 and 10) were the most common set. The parents and hybrids differed markedly in their chromomeric pattern, chromatin length, and arm ratio.
The most frequent chromosomal aberrations observed were loose pairing at pachytene, univalents, and quadrivalents at diakinesis and metaphase I, bridges and late disjunction at anaphase I, and bridges and laggards at telophase I.
Based at pollen and spikelet counts, only O. nivara, O. nivara×TNl and O. nivara×Dgwg were partially sterile. The other F₁ hybrids were fertile. The difference between the pollen and spikelet sterilities in most hybrids and parents may be due to environmental effects. There was no direct relationship between the meiotic aberrations observed and the sterility of the F₁ plants.
Chromosome pairing was essentially normal in all F₁ plants and most of them are fertile, indicating that the O. nivara accession and the O. saliva cultivars have the same genome composition (AA). There is close affinity between IRRI Acc. 101508 and the O. sativa cultivars.