Effects of sorghum (sorghum bicolor L.) root exudates on the cell cycle of the bean plant (phaseolus vulgaris L.) root

Two experiments were conducted to test the allelopathic effect of sorghum (Sorghum bicolor L.) root exudates on bean (Phaseolus vulgaris L.) cell division. Research was conducted in the greenhouse of the Wistock Agricultural Research Institute of Minas Gerais State (EPAMIG) and in a laboratory of the Federal University of Lavras (UFLA). Sorghum variety BR-601 and bean variety Carioca MG were used. The exudate, called sorgoleone (SGL), was obtained by methylene chloride and acetic acid extraction from sorghum roots seven days after sowing on Petri dishes, and refrigerated until use. Solutions of 0.01, 0.05, 0.10, and 0.15 mM were prepared using Johanson solution as the SGL solvent. Seven-day-old bean seedlings grown in vermiculite in a greenhouse were transplanted to the solution. Seven days after transplantation, the beans did not show any sign of phytotoxicity; however, cytogenetic observations showed that SGL reduced the number of cells in prophase, metaphase, and anaphase stages. Colchicine effects were observed among cells in metaphase on the third and fifth days after treatments and varied with SGL concentrations. By the seventh day, the colchicine effects were inversely proportional to concentration, which varied from 34.3% for 0.01 mM to 6.6% for 0.15 mM. SGL acts as a mitotic inhibitor. It probably depolymerizes the microtubular proteins and induces the formation of colchicine metaphases causing polyploid nuclei. A largest period of SGL treatment also induced chromosome breaks and bridge formation in anaphase and telophase. Although SGL cannot be used as a herbicide for bean cultures, its allelochemical effects on other cultures are the factors that will define the use of sorghum as a natural herbicide.