Bioherbicidal effect of fumonisin B ₁ , a phytotoxic metabolite naturally produced by <i>Fusarium nygamai</i> , on parasitic weeds of the genus <i>Striga</i>

Abstract

Fusarium nygamai has been isolated and identified from diseased Striga hermonthica plants collected from sorghum fields in the Sudan. Fumonisin B1, produced by this fungus, was isolated and purified. In in vitro experiments, the bioherbicidal potential of this mycotoxin was evaluated against S. hermonthica and S. asiatica. Different concentrations (250, 500 and 1000 μg L−1 of water) of fumonisin B1, applied during the conditioning phase of the Striga seeds significantly reduced the germination of both species in a range of 19.8–32.2 and 34.5–47.6%, respectively. In addition, the length of the germ tubes was reduced and the germ tubes became brownish. Fumonisin B1 slightly delayed the emergence of Striga when 250 mg fumonisin B1 dissolved in 1 L of water were applied into the soil per pot before sowing sorghum. By the way of contrast, fumonisin B1 was very phytotoxic when Striga seedlings (leaves and stems) of different heights and ages were sprayed with a concentration series of 250, 500 and 1000 μg fumonisin B1 mL−1 until run-off, or when plants were injured with a scalpel before fumonisin B1 was applied into the injury at concentrations of 250 and 500 μg mL−1. One day after application, the plants showed symptoms of wilting, first at the top and then moving downwards. Leaves turned black and stems desiccated at the point of injuries. Within 4 days after the application, 55% of the plants tested were completely destroyed. In total, at the end of the experiment, 40 days after the treatment, 85% of the treated plants were killed by fumonisin B1, regardless of the concentration applied and the application technique used.