Abstract
Cytological investigations of the microsporogenesis in male-sterile (MS) ramie (Boehmeria nivea var. ‘Miyasaki’) and its offspring were carried out. Fourteen bivalents were observed at the totality of the analyzed diakinesis and metaphase I cells. A low percentage of laggard and sticky chromosomes was seen in anaphase I and II. In MS plants, however, a degenerative process started at the tetrad stage. Callose became thicker in comparison to male-fertile (MF) plants and could not be disrupted. The four microspores enclosed by callose were smaller and connected to each other, probably due to incomplete cytokinesis. The amorphous and shriveled remnant structures presented distinct size and cytoplasmic content. At the same time, a degenerative process took place in young male buds which fell down before anthesis. Cytomictic channels were also observed between PMCs in one or more meiotic stages from pachytene to telophase II in all plants examined and pollen grains with different cytoplasmic content observed in MF plants were interpreted as consequence of cytomixis. Male sterility in ramie appears to be controlled by a recessive gene instead of cytoplasmic factors due to the fact that crossing male-sterile (as female parental) with male-fertile produced MS and MF plants. Ramie male sterility may be a valuable tool to be explored in breeding programs for fiber and/or forage purposes since asexual reproduction assures the maintenance of MS genotypes in the field.
