Allelopathic Effects of Sorghum/Sorghum-Sudangrass Hybrids Against <i>Rotylenchulus reniformis</i>

Reniform nematode (<i>Rotylenchulus reniformis</i>) 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 <i>R. reniformis</i> 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 (<i>P</i> ≤ 0.05) and suppressed <i>R. reniformis</i> development in cowpea roots (<i>P</i> ≤ 0.05). In Trial I, 2-month-old amendments showed the greatest suppression, whereas in Trial II, 1-month-old amendments were more suppressive (<i>P</i> ≤ 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 <i>R. reniformis</i> infecting cowpea roots (<i>R</i>² = 0.69; <i>P</i> = 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.