Comparative histology of embryogenic cell and somatic embryo initiation in callus cultures of mungbean (Vigna radiata (L.) Wilckzek) pole sitao (V. unguiculata (L.) Walp. var. equipedalis (L.) Koern.) and mothbean (V. aconitifolia (Jacq.) Marechal)

Histological examinations of cotyledon- and leaf-derived callus cultures of mungbean (Vigna radiata (L.) Wilczek),pole sitao (V.unguiculata (L.) Walp. var. sesquipedalis (L.) Koern., and moth bean (V. aconitifolia Jacq. Marechal) initiated using MS-B5 medium with three different auxins were done to determine the origin and development of embryogenic cells and somatic embryos. This was aimed at explaining the inherent difficulty in affecting plant regeneration by somatic embryogenesis from callus cultures in the genes Vigna. Five-d-old cotyledons of pole sitao cv.UPLPS2 and mungbean cv. Pag-asa 3 inoculated in 20 mg/L 2,4-D, and of pole sitao cv. UPLPS2 and mungbean cv Pag-asa 7 grown in 10mg/L dicamba formed cambium-like zone due to active division of perivascular cells. This was also observed in leaf sections of pole sitao cv. UPLPS1 cultured in 20 mg/L 2,4 D and 10 mg/L picloram, and from established callus cultures of moth bean maintained in 2 mg/L, 2,4-D and 0.5 mg/L BAP.The presence of the cambium-like zones resulted in the formation of globular proembryoids from meristematic mass of cells. A small number of somatic embryo originating from single cell resembling zygotic embryo in origin and morphology was observed in pole sitao cv. UPLPS1 inoculated in 10 mg/L picloram.The proembryonic structures and somatic embryos in mungbean and pole sitao were not observed to differentiate into more advanced stage as evidenced by the absence of meristenoids in 3-and 4-wk-old cultures.On the other hand, various advanced stages of somatic embryogenesis originating from mass of cells were observed in established callus cultures of mothbean accs. 3374 and 3381. In addition, clumps of embryogenic individual cells at different stages were noted within the same explant in acc. 3381. Various modifications on the tissue culture medium conditions are recommended to enhance the proliferation of meristenoids allow subsequent differentiation of the proembryoids and eventually achieve regeneration in the recalcitrant mungbean and pole sitao.