USE OF CRUDE EXTRACTS OF Ageratum conyzoides FOR THE CONTROL OF BLACK POD DISEASE OF CACAO CAUSED BY Phytophthora megakarya

Abstract

Black pod disease caused by Phytophthora spp., is one of the most destructive diseases affecting cacao (Theobroma cacao) globally. Hence, the need for the use of plants such as (goatweed) Agerantumconyzoides known for itsenvironmentally-friendly antimicrobial properties, as possible replacements to chemical fungicides. This study aimed to evaluate the in vitro antifungal efficacy of aqueous leaf extracts of Ageratum conyzoides at different concentrations against Phytophthora megakarya, the causal agent of cocoa black pod disease. Aqueous extracts of air-dried A. conyzoides leaves were prepared at varying concentrations (5%, 10%, 15%, and 20%) and tested in vitro against a pathogenic laboratory isolate of P. megakarya using food poisoning technique. The mycelial radial growth observed on each treatment was measured on the 5th, 7th and 9th days after inoculation. Percentage mycelial inhibition was   calculated and data were subjected to analysis of variance (ANOVA) using Tukey HSD Test at p˂0.05. Average percentage inhibition (45.64%) exhibited at  15% concentration of the aqueous extract was significantly higher p<0.05  than those of 5%, 10% and 20% extract concentrations on Day 5. There was no significant difference (p<0.05)  in the percentage mycelial inhibition between the 10% and 20% extract concentrations on days 7 and 9. Fungicide (Ultimax) used as positive control (54.07 – 59.77%) however, had  significantly (p<0.05) highest mycelial inhibition) throughout the incubation period. Results obtained from the study showed that 15 and 20% concentrations of the extract, compared favourably  with the chemical fungicide in the control of mycelial growth  and sporulation of P. megakarya. Further research, however, need to be done in situ to ascertain the antifungal potentials of A. conyzoides aqueous extracts as costeffective  and environmentally-friendly alternatives for managing cocoa black pod disease.