Response of Bradyrhizobium japonicum nodule variables to cucurbitacin-containing phytonematicides in cowpea (Vigna unguiculata L.) on N-deficient soil

Abstract

The Curve-fitting Allelochemical Response Data (CARD) had been adopted to develop the non-phytotoxic concentration of phytonematicides, technically referred to as the mean concentration stimulation point (MCSP). The MCSP for cucurbitacin-containing phytonematicides on Bradyrhizobium-nodulated legume crops had not been documented in low-input agricultural farming systems. The objective of this study was to determine the MCSP values of Nemarioc-AL and nemafric-BL phytonematicides on B. japonicum-nodulated cowpea (Vigna unguiculata) on nitrogen-deficient soils. Inoculated cowpea seeds were sown in 20-cm diameter plastic pots containing steam-pasteurised N-deficient loamy soil and Hygromix at 3: 1 (v/v) ratio. Two parallel experiments comprised Nemarioc-AL and Nemafric-BL phytonematicides, each had seven treatments (0, 2, 4, 8, 16, 32 and 64%) and applied once weekly. At 56 days after the treatments, the MCSP values for Nemarioc-AL and Nemafric-BL phytonematicides on cowpea were 5.4 and 6.3%, respectively, with the overall sensitivity (Σk) of one for each phytonematicide. In conclusion, the observed MCSP and Σk values suggested that the two cucurbitacin-containing phytonematicides were suitable for Bradyrhizobium-nodulated cowpea production systems on N-deficient soils.