Biocontrol Potential of Chitin and Chitosan Extracted from Black Soldier Fly Pupal Exuviae against Bacterial Wilt of Tomato

Abstract

Globally, Ralstonia solanacearum (Smith) is ranked one of the most destructive bacterial pathogens inducing rapidly and fatal wilting symptoms on tomato. Yield losses on tomato vary from 0 to 91% and most control measures are unaffordable to resource poor farmers and ineffective. This study investigated the biocontrol potential of chitin and chitosan extracted from black soldier fly (BSF) pupal exuviae by chemical methods against R. solanacearum. Ralstonia solanacearum was isolated from soil samples collected from JKUAT tomato growing fields. Morphological, biochemical, and molecular techniques were used to characterize isolated R. solanacearum for in vitro and in vivo experiments. All experiments were done in triplicates and all data were expressed as means ± standard error. One-way analysis of variance (ANOVA) was used to test difference in means and means were separated using the Bonferroni range test. Results revealed that at higher concentration (5%w/v) BSF chitosan significantly inhibited in vitro growth of R. solanacearum by 19.83 ± 1.17 mm when compared to 1% acetic acid (11.67±2.35 mm). However, there was no significant difference in the antibacterial activities between BSF pupal exuviae chitosan and commercial chitosan against R. solanacearum (p˃0.05). Cocopeat amended with 20 g BSF-chitin and 20 g chitosan demonstrated a reduction in bacterial wilt disease incidence by 30.31% and 34.95%, respectively. On the other hand, disease severity was reduced by 22.57 and 23.66 % when inoculated tomato plants were subjected to cocopeat amended with BSF chitin and chitosan, respectively. These findings show that BSF pupal shells are an attractive renewable raw material for the recovery of valuable products (chitin and chitosan) with promising eco-friendly management option for bacterial wilt R. solanacearum. Further studies should explore integrated pest management options that involve multiple components including insect-based chitin and chitosan to manage bacterial wilt disease and contribute to increased tomato production.