The role of the diffuse stage in the cytological problems of meiosis in Rosa.

Abstract

A technique involving denaturation - reassociation for the staining of different stages of meiosis in squash preparations has been standardised. Based on this technique, observations on meiosis in diploid and hexaploid Rosa plants as well as in a hybrid between them are presented. A diffuse stage at early diplotene was observed in which the bivalents lose their distinct morphology and the nucleus is filled with a network of fine fibrils. In both parent plants, restitution of bivalents from the diffuse stage occurs easily and at diakinesis fully condensed and regular bivalents are usually found. In the hybrid plant, however, the restitution from diffuse stage chromosomes to the fully contracted ones appears to be affected, the chromosomes often entering the metaphase stage before reaching full contraction. Varied multivalent-like configurations were found which are probably due to the irregular restitution of chromosomes and to the remains of the fibrillar structures from the diffuse stage. The origin and the nature of the multivalent-like formations found in hybrid Rosa plants is not clear.