The potential of thiarubrine C as a nematicidal agent against plant-parasitic nematodes

Thiarubrine C, a polyacetylenic 1,2-dithiin isolated from the roots of Rudb eckia hirta (Asteraceae), exhibited strong nematicidal activity in in vitro and growth chamber assays. Thiarubrine C was toxic, in the absence of ligh t, to the plant-parasitic nematodes Meloidogyne incognita and Pratylenchus penetrans at LC(50)s of 12.4 ppm and 23.5 ppm, respectively. A minimum expo sure time between 12 and 24 hours was the critical period for nematode mort ality due to thiarubrine C. Although thiarubrine C was not totally dependen t on light for toxicity, activity was enhanced in the presence of light, es pecially with the microbivorous nematode, Teratorhabditis dentifera. Upon e xposure of M. incognita juveniles to 20 ppm thiarubrine C for 1 hour, infec tion of tomato plants was greatly reduced compared to untreated checks. Thi arubrine C was also effective in reducing plant infection when mixed with s oil 24 hours prior to or at planting, unlike other related compounds such a s partial derivative-terthienyl.