Characterisation of Phaeoisariopsis Griseola, Phytochemical Screening and Fungicidal Activity of Selected Plant Extracts Against Phaeoisariopsis Griseola of Common Bean Var. Glp 1127 (Mwezi Moja) Maseno, Kenya
Simon Meso OBILA
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v ABSTRACT Angular leaf spot disease (ALS) caused by Phaeoisariopsis griseola is a major constrain of common bean leading to production of less than 25% of the potential yield thus posing a chronic threat to food security in Kenya. Synthetic fungicides are primarily preferred in the management of ALS although it’s use is becoming restrictive due to a number of shortcomings. Azadirachta indica, Allium sativum and Tithonia diversifolia plant extracts have demonstrated successful antimicrobial activity against plant pathogens and are gaining popularity as they are safe to use, easily available and cheap. Little though is known about the success of using these crude extracts to manage ALS. The aim of this study was to characterise Phaeoisariopsis griseola, phytochemically screen and determine fungicidal activity of Azadirachta indica, Allium sativum and Tithonia diversifolia extracts against Phaeoisariopsis griseola. The study was conducted at Maseno University. Plant specimens were taxonomically identified and authenticated then air-dried and fine ground for extraction using methanol, ethanol and distilled water. Phaeoisariopsis griseola from Ugenya, Bondo and Sabatia sub-counties were isolated for morphological profiling and pathogenicity tests. The plants specimens were screened for phytochemicals. Inhibition of spore germination of Phaeoisariopsis griseola was determined at concentrations of 50, 75 and 100% In vitro. Synthetic fungicide and water were used as positive and negative controls respectively. In vivo evaluations were conducted in the greenhouse in a completely randomized design with four replications. The experimental plants were inoculated with 60ml suspension 2.5 x 106 spore/ml of Phaeoisariopsis griseola 5 weeks from emergence. Two weeks later, the plants were sprayed with 100% concentration methanolic extracts. Data on morphological profiling was assessed under a light microscope after 14 days incubation at 25oC. Data on pathogenicity tests was scored on being pathogenic or not pathogenic. Data on phytochemical screening was scored for presence or absence of specific phytochemicals, Inhibition zones were measured in millimetres, growth, yield and disease index were collected 8 weeks from emergence and the data collected subjected to Analysis of Variance (ANOVA) and treatment means separated and compared using LSD (P=0.05). Morphological profiling of isolates revealed variations in terms of hyphae and spores’ characters. Alkaloids, tannins, flavonoids, terpenoids, saponins, cardiac glycosides and sterols were present in nearly all the plant specimens with flavonoids being absent in Azadirachta indica and sterols, saponins and alkaloids being absent in Tithonia diversifolia. All the plant extracts significantly inhibited spore germination of Phaeiosariopsis griseola (P≤0.05). The most effective was methanolic Allium sativum extract at 100% concentration. Among the plant extracts Allium sativum In vivo had the highest fungicidal effect proportionate to the concentration percentages. Methanol had the highest extraction potential while water solvent had the least effect. The extracts had higher significant effect on growth index, yield components and disease index (P<0. 001). From this study plant extracts of Azadirachta indica, Tithonia diversifolia and Allium sativum had higher potential for pathogen control at higher concentrations (100%) hence are recommended as potential botanicals for the control of ALS disease of common bean Var. GLP 1127 Mwezi moja.