Potency of Plant-based Fungicides against a Rot Pathogen of White Yam (Dioscorea rotundata Poir)

Abstract

Aims: This study assessed the in vitro antifungal potential of crude extracts of ten plants on the mycelial dry weight and spore germination of Botryodiplodia theobromae using hyphal extension bioassay. Study Design: The experiment was a 10 x 2 x 6 factorial laid out in a Completely Randomized Design (CRD) and replicated three times. Means were separated using LSD (P<0.05). Place and Duration of Study: Department of Botany, University of Calabar, Calabar and National Roots Crop Research Institute, Umudike both in Nigeria. The study was carried out between May 2015 and March, 2016. Methodology: The plant materials of Afromomum melegueta, Zingiber officinale, Allium sativum, Cola attiensis, Ocimum gratissimum, Xylopia aethiopica, Piper guineense, Garcina cola, Monodora myristica and Senna occidentalis were extracted in water and ethanol. Infected yams were collected and packaged in sterile polythene bags and taken to the laboratory for isolation of microorganisms and isolates identified. The pathogenicity of the isolates used was confirmed using axenic cultures. Results: Solvent of extraction and concentration of the extracts exerted significant influence on the performance of the extracts. Water extract treatments of Aframomum melegueta and Zingiber officinale were the best and comparable (P<0.05) in reducing spore germination each recording a value of 97%. The most impressive result obtained for ethanol extracted plant material was a 100% spore reduction value recorded for Z. officinale at 100 g/l concentration. Seeds of Aframomum melegueta and rhizomes of Zingiber officinale extracted in both water and ethanol were superior in reducing the mycelial biomass of B. theobromae compared to others. Water extracts of Aframomum melegueta and Zingiber officinale reduced the mycelial biomass of the test pathogen by 84.7% and 85.7% at 100 g/l concentration respectively. Their performances were comparable (P<0.05). Extracts of Allium sativum and Cola attiensis recorded the least spore germination reduction and mycelial dry weight reduction values irrespective of the solvent of extraction. No growth reduction was evident in the control treatments throughout the course of the study. Conclusion: All the plant extracts tested inhibited the growth and development of B. theobromae to varying degrees. Solvent of extraction and concentrationof the extractsexerted significant influence on the performance of the extracts.