Hot Water Treatment Enhances the Bioherbicidal Efficacy of a Fungus

C Douglas Boyette,Kenneth C Stetina,Robert E Hoagland

doi:10.4236/ajps.2018.910150

Abstract

Hemp sesbania (Sesbania exaltata) plants (>30 cm tall) sprayed with hot water (45°C – 95°C), followed by spray applications of fungal spores of Colletotrichum truncatum (CT) at 1.0 × 107 spores/ml-1 and 22°C – 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 without 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 without 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.

Highlights

Inoculation tests revealed that spores were highly virulent to hemp sesbania plants (30 cm tall), i.e., ~100% mortality of inoculated plants 5 days after treatment (DAT) when plants received a hot water (65 ̊C) pre-treatment, fb spray treatment of Colletotrichum truncatum (CT) formulated in SW and/or corn oil (CO) (Figure 3)
SW and SW+CO applications without CT had no effect on mortality or dry weight reduction of hemp sesbania plants when applied following a pre-treatment of water at temperatures of 25 ̊C - 35 ̊C, followed by a 12-h dew period (Figure 4(a) & Figure 4(b))
Hemp sesbania plants (>30 cm tall) sprayed with hot water (65 ̊C - 95 ̊C), followed by spray applications of fungal spores of Colletotrichum truncatum (1.0 × 107 spores∙ml−1) were controlled 90% - 95% under greenhouse conditions and 75% - 85% under field conditions, 15 DAT

Summary

Introduction

Exposure to a flame for only 0.065 - 0.130 s was sufficient to kill leaf tissue [5] [8] and higher temperatures were more effective. Cellular structural changes were more pronounced when the cellular temperature changed more rapidly (e.g., flaming) compared to gradual and lower temperature changes (e.g., hot-water treatment) [5]. Since many of these treatments only kill plant shoots, the affected plants (especially perennial weeds) may regenerate, making repeated treatments necessary [1] [2]

Methods

Results

Conclusion