Hot water treatment enhances the bioherbicidal efficacy of a fungus

Authors: Boyette, Clyde; Hoagland, Robert; Stetina, Kenneth - Ken

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2018
Publication Date: 9/28/2018
Citation: Boyette, C.D., Hoagland, R.E., Stetina, K.C. 2018. Hot water treatment enhances the bioherbicidal efficacy of a fungus. American Journal of Plant Sciences. 9(10):2063-2076.

Interpretive Summary: A process was developed to enable the bioherbicidal fungus, Colletotrichum truncatum, to control large hemp sesbania (>30 cm), a glyphosate-tolerant, problematic weed in southern U.S. rowcrops, using a hot water pre-treatment. In greenhouse tests, we found that when hemp sesbania plants were sprayed with hot water (45-95° C), followed immediately by spray applications of fungal spores suspended in either 0.2% Silwet L-77 surfactant in water or unrefined corn oil, or in corn oil, 80-95% control was achieved 12 days after treatment, with concomitant plant dry weight reductions. Plants treated with hot water formulations without the fungus were also damaged at temperatures =45° C, but at greatly reduced levels. Artificial dew treatments (25° C, 12 h), combined with the treatment protocols above, had no effect on weed mortality or dry weight reduction. Over 80% control of hemp sesbania was achieved after 12-15 days in replicated field experiments when a pre-treatment of hot water (65° C) was followed with fungal applications as described. Plants in field tests treated with the fungus without the hot water treatment were unaffected. These results suggest that hot water treatment may be useful for improving the bioherbicidal potential of plant pathogens.

Technical Abstract: Hemp sesbania (Sesbania exaltata) plants (> 30 cm tall) sprayed with hot water (45-95° C), followed by spray applications of fungal spores of Colletotrichum truncatum (CT) at 1.0 x 107 spores ml-1 and 22-25° C, suspended either in: 0.2% Silwet L-77 surfactant (SW); unrefined corn oil (CO)/distilled water (1:1, v:v); or 0.2% SW in CO were controlled by 80-95%, 12 days after treatment (DAT) under greenhouse conditions. These treatments also reduced dry weight accumulation of this weed. Plants treated with hot water sans CT were also injured at temperatures =35° C, (5% mortality) and 60% mortality at 95° C. Artificial dew treatments (25° C, 12 h), imposed on plants after the treatment protocols above, had little or no effect on weed mortality or dry weight reduction compared to treated plants without dew. Under field conditions, 85% control of hemp sesbania was achieved 12-15 DAT when a pre-treatment with hot water (65° C) was followed immediately with a CT application at the spore concentration as described above. Plants in field tests treated with CT sans a hot water treatment were visually unaffected, with no mortality or plant biomass reductions recorded 15 DAT. These results suggest that use of hot water may be an important tool for improving the infectivity and bioherbicidal potential of some plant pathogens.