Toxicity of tomatine and tomatidine on weeds, crops and phytopathogens fungi

α-Tomatine was not highly phytotoxic and slightly inhibited the stem elongation (7 to 13%) when applied as a spray to etiolated 4-day-old seedlings of sesbania [Sesbania exaltata (Raf.) Rybd.], sicklepod (Senna obtusifolia L.), mungbean (Vigna radiata L.), wheat (Triticum aestivum L.) and sorghum (Sorghum vulgare L.). Tomatidine had less effect on stem elongation than tomatine and reduced the elongation (5 to 10%). Tomatine was more effective than tomatidine in reducing chlorophyll content in excised etiolated tissues of hemp sesbania, sicklepod, mungbean, wheat and sorghum. Inhibition of chlorophyll accumulation by tomatine ranged from 16 to 89% of control values, whereas inhibition by tomatidine ranged from 0 to 30% of control in these species. Both tomatine and tomatidine increased electrolyte leakage of corn (Zea mays L.), kudzu [Pueraria lobata (Willd.) Ohwi], palmleaf morningglory (Ipomea wrightii Gray) and wild senna (Cassia marilandica L.) leaf disks at 24 to 72 h after exposure to the compounds (0.5 mM) and light (100 μE m² s⁻¹). Tomatidine caused greater electrolyte leakage than tomatine in tissues of these species. When incorporated into growth media (agar) at 0.3 mM, tomatine and tomatidine inhibited the growth of three fungal bioherbicidal phytopathogens. Alternaria cassiae (weed host = sicklepod), the most sensitive pathogen was inhibited 70% by both compounds. Tomatine inhibited Colletotrichum truncatum (weed host = hemp sesbania) and Fusarium subglutinans (produces fumonisin, phytotoxic to many plants) growth by 63% and 50%, respectively; while tomatidine inhibited the growth of these latter two pathogens by 50% and 15%, respectively. These natural plant products were shown to have a broad range phytotoxicity and fungitoxicity which may be important in plant defense mechanisms.