Browsing by Author "Vedasto, Victor"

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    Antifungal Potential of Plant Bioactive Compounds, Sulphur and Copper Formulations against Alternaria brassicicola (Schwein.) Infecting Kales in Kiambu County, Kenya
    (Kenyatta University, 2025-07) Vedasto, Victor
    Kale is the most popular and majorly consumed green vegetable in both rural and urban settings in Kenya. It is cultivated by more than 90% of smallholder farmers in the country. One of the major biotic constraints hampering kale production in Kenya is Alternaria leaf spot (ALS) caused by Alternaria brassicicola. Most farmers manage the disease with the use of synthetic fungicides, which is not a sustainable approach. This study was conducted in Kiambu County to (i) determine the occurrence, prevalence, farmers’ knowledge, and current management practices for ALS in kales; (ii) evaluate the cultural, morphological, and molecular features of A. brassicicola isolates infecting kales and (iii) evaluate efficacy of bioactive compounds present in Jatropha curcas, Tephrosia vogelli, Persea americana, Cymbopogon citratus, Ocimum gratissimum, and Carica papaya extracts and selected Sulphur commercial formulation (WETSULF® 80% w/w, THIOVIT® JET 80% w/w) and Copper (VIFRA® 40 WG, ISOCAP® 50WP) against A. brassicicola invitro. A survey was conducted in 180 kale fields, ninety (n=90) fields in Githunguri and (n=90) fields in the Lari sub-county, using a semi-structured questionnaire. The fresh kale leaves depicting the typical symptoms of ALS were collected, and 3-5 leaves from each plant were collected and transported to the Kenyatta University agriculture laboratory for analysis, where a total of 120 A. brassicicola isolates were obtained. The result revealed that ALS is prevalent in most kale fields (80-85%) in both sub-counties, and 57.2% of respondents manage the disease using fungicide; 45% of farmers reported the fungicide to be either less effective or ineffective. The other method used to manage the disease was the removal (pruning) of the infected leaves or plants by 33% of the total farmers. A test on farmers' knowledge of ALS and its management revealed that most respondents had knowledge ranging from low to medium. The cultural and morphological study of isolates revealed that most isolates were not significantly different from one another. When isolates were characterized at the molecular level, their sequences exhibited a low genetic diversity, and they fell into two Clades. The overall genetic distance (d) was 21%, while among Githunguri isolates it was 28% and 8% for Lari isolates. Other isolates were found to belong to other species of Alternaria, e.g. A. alternata, A. altra, and A. aborescens, suggesting that ALS in the study area is inflicted by not only A. brassicicola but also other Alternaria species. Among six plant species tested, the bioactive compounds from J. curcas (62.2% at 2000mg/ml, 69.9% at 4000mg/ml) followed by T. vogelli (60.3% at 2000mg/ml, 64.4% at 4000mg/ml) showed mycelial inhibition of ≥ 50 % at the 10thday after inoculation of A. brassicicola. The degree of mycelial inhibition at 4000mg/ml was significantly higher than at 2000mg/ml. Two sulphur formulations, THIOVIT JET 80W/W, which achieved pathogen growth inhibition by 68%, and WETSULF 80W/W by 64.5%, and only one Copper formulation, VIFRA 40WG (66%), were effective (≥50%) against the pathogen at their manufacturer’s recommended dosage levels. These findings suggest that bioactive compounds from J. curcas and T. vogelli are good candidates that can be considered in the commercial manufacture of control products for ALS. Most of the Copper and Sulphur formulations are effective against ALS and thus can be used by farmers as part of the Integrated Disease management strategy. For effective management of ALS, product manufacturers should take into account the genetic variability of A. brassicicola but also other Alternaria species that cause similar symptoms. Furthermore, there is a need to capacitate kale farmers on precise identification, early and sustainable management of ALS