Relationship Between Levels of Cyanide in Sudangrass Hybrids Incorporated into Soil and Suppression of Meloidogyne hapla.

Sudangrass cv. Trudan 8 has been demonstrated to suppress infection of vegetables by Meloidogyne hapla (Mh). Hydrogen cyanide, released from the degradation of the cyanogenic glucoside (dhurrin) during decomposition of Trudan 8, was the primary factor involved in suppression of Mh on vegetables. The cyanide ion level in leaf tissue of 14 hybrids of sudangrass varied between 0.04 (cv. SX-8) to 1.84 parts per million (cv. 840F). The suppressive activity of the sudangrass hybrids against Mh was assessed in greenhouse tests by incorporating various amounts of leaf tissue into organic soil. After 1 week, eggs of Mh were added to the soil (8 eggs/cm[sup3] soil), which was then planted with lettuce as a bioassay plant. After 8 weeks, the lettuce roots were washed and rated for root-gall severity (RGS). Incorporation of sudangrass tissue resulted in a reduction of RGS up to 54%. There was a correlation between the amount of free cyanide incorporated into the soil and the reduction in RGS. Other green manures of cyanogenic plants tested were white clover, which resulted in a 45% reduction in RGS, and flax, which resulted in a 53% reduction in Mh penetration of lettuce roots. These results suggest that cyanogenic plants have potential as nematicidal green manures.