Abstract
Histological peculiarities of the abscission layer between pedicel and spikelet were investigated in Asian rice, African rice, their putative ancestral wild species, and the other nine wild Oryza species. As in the African rice (O. glaberrima Steud.), both the normally developed and partially developed abscission layers were found in the African rice's ancestral wild species (O. barthii). In other wild Oryza species including the putative ancestral wild species (O. rufipogon and O. nivara) of Asian rice (O. sativa L.), only the normally developed abscission layer was found. In these wild oryza species, the parenchymatous cells of the abscission layer cracked completely at maturity time, except for the wild species O. longistaminata. In the African ancestral wild species, sclerenchymatous cells were situated around the central vascular tissue, while any sclerenchyrmatous cells were situated in the other wild Oryza species. At maturity time, therefore, the thickness of the supporting zone consisting of the central vascular tissue and the sclerenchymatous cells was greater in the African ancestral wild species than in the other wild Oryza species. As the result the latter was essentially more fragile. According to its shape, the abscission layer was classified into three types : curved, straight, and sunken. All the wild rice plants belonging to the A genome species had the curved type of abscission layer.
