Allelopathic Effects of Sorghum/Sorghum-Sudangrass Hybrids Against Rotylenchulus reniformis

Reniform nematode (Rotylenchulus reniformis) is a damaging and difficult-to-manage pest on many agricultural crops. Sorghum and sorghum-sudangrass hybrids (SSgHs) have shown potential in managing plant-parasitic nematodes by releasing toxic hydrogen cyanide gas through the hydrolysis of dhurrin, a cyanogenic glucoside found in leaf epidermal cells. The objectives of this study were to evaluate the effect of different SSgH varieties and their age on the suppression of R. reniformis and to quantify their dhurrin contents. Shoot biomass of seven SSgH varieties was harvested at 1, 2, and 3 months of growth and used as a soil amendment in two greenhouse cowpea bioassay trials. Dhurrin concentration was analyzed using high-performance liquid chromatography from 2-month-old tissues. The results indicated that energy sorghum 'NX-D-61' and SSgH 'Latte' exhibited the highest dhurrin concentrations (P ≤ 0.05) and suppressed R. reniformis development in cowpea roots (P ≤ 0.05). In Trial I, 2-month-old amendments showed the greatest suppression, whereas in Trial II, 1-month-old amendments were more suppressive (P ≤ 0.05). Potential effect of environmental stress on dhurrin concentration in SSgH tissue was discussed. Nonetheless, dhurrin concentrations were negatively related to the number of R. reniformis infecting cowpea roots (R² = 0.69; P = 0.02). These findings suggest that high-dhurrin SSgH varieties can be integrated into reniform nematode management plans as a cover crop and terminated no more than 2 months after planting.