Interference potential of Pluchea lanceolata (Asteraceae): growth and physiological responses of asparagus bean, Vigna unguiculata var. sesquipedalis

The water-soluble compounds synthesized by the weed, Pluchea lanceolata, and released by it into the soil significantly reduced seed germination, number of nodes, internode length, shoot and root lengths, nodule number and weight, and Chl a and b and Chl a/b ratio of asparagus bean plants. The pattern of accumulation of nutrients in shoot and root of asparagus bean was also affected. In contrast, the net photosynthetic rate and stomatal conductance of fully expanded leaves were higher in plants grown with treated soil. The concentrations of Mg++, Zn++, and PO4(3-) were higher and K+ was lower in shoots of plants grown with treated soil as compared to those grown with the control soil. Also, roots of plants grown with treated soil showed greater accumulation of Mg++ and NO3-. Shoot/root ratio of nutrients in plants grown with control soil were higher for Zn++, Na+, Ca++, and NO3-, whereas plants grown with treated soil had higher ratios for PO4(3-). These results provide evidence for allelopathic interference by P. lanceolata to the growth of asparagus bean.