Fungal entomopathogens are the most effective biocontrol agents against insect pests in the natural ecosystem. This study was conducted for phenotypic, molecular, and virulence characterization of locally isolated entomopathogenic fungi from soil samples of six localities in Ethiopia. Entomopathogenic fungi were isolated from 120 soil samples with the galleria baiting method. A total of 65 (54.2%) entomopathogenic fungal isolates belongs to Beauveria spp and Metarhizium spp were identified based on cultural and morphological features. All isolates were pre-screened based on germination, vegetative growth rate, and spore production as fungal in-vitro virulence determinates. Isolate AAUKB-11 displayed the peak germination of 99.67% and isolate AAUMFB-77 achieved the highest radial growth rate of 3.43 mm day À1 with the highest sporulation 4.60 Â 10 8 spores/ml. The phylogenetic analysis of ITS-rDNA confirmed that 7 isolates were identified as B. bassiana and 5 isolates were categorized into M. anisopliae. Selected B. bassiana and M. anisopliae strains were evaluated for their pathogenicity efficiency against G. mellonella larvae and caused 86.67%-100% mortality. The mortality rates of G. mellonella larvae peaked at 100% with 4(33.33%) isolates from B. bassiana and 2(16.67%) isolates from M. anisopliae after 10 days of treatments. The high virulent isolate, B. bassiana AAUMB-29 displayed the least LT 50 value of 2.36 days followed by isolate B. bassiana AAUMFB-77 with LT 50 of 2.53 days. Future studies should be needed to focus on the evaluation of high virulent isolates against other potential insect pests to assess their vigorous role as favorable biological control agents.
Background Bacillus thuringiensis is a Gram-positive, rod-shaped, and spore-forming microbial entomopathogen. The silverleaf whitefly, Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae), is a worldwide important cryptic species causing serious economic damage to several vegetable crops including tomato. The aim of this study was to characterize and evaluate the bio-insecticidal effects of locally isolated Bacillus thuringiensis (Bt) against Galleria mellonella and Bemisia tabaci. Results Thirty-one isolates of Bt were obtained from 70 soil samples based on cultural characterization coupled with insecticidal crystal protein detection. All of the 31 bacterial isolates were pre-screened for their bio-insecticidal property against the greater wax moth, Galleria mellonella L. larvae. Only 20 (64.5%) isolates were virulent to G. mellonella with a percentage mortality that ranged from 2.50 to 95%. The groEL gene sequences of all 20 entomopathogenic indigenous isolates displayed 99–100% similarity with Bt isolates. Bioassay evaluation of 12 selected isolates against 3rd to 4th nymphal instars of B. tabaci with spore-crystal suspensions of 1 × 109 spores/ml caused 0 to 31.25%, 0 to 57%, and 0 to 82.5% percentage mortality within 48, 96, and 144 h accordingly. Among isolates of Bt, isolate AAUDS-16 had the highest virulence, followed by the isolate AAUES-69D with LC50 values of 9.67 × 106 spores/ml and 1.16 × 107 spores/ml, respectively. The virulent isolates were tested for their growth response to a different temperature range between 15 and 40 °C. All isolates showed a maximum growth rate around 30 °C. Conclusions Bt isolates of AAUES-69D and AAUDS-16 displayed high insecticidal potential against B. tabaci nymphs and G. mellonella larvae, and showed a maximum growth rate in a wide range of temperature. High virulence and temperature-tolerant isolates should be important candidates for diverse insecticidal toxin studies.
Objective This study was aimed to assess the enzymatic activity and pathogenicity potential of Beauveria bassiana and Metarhizium anisopliae against whiteflies in Ethiopia. Results The data showed that Beauveria bassiana AAUMB-29, AAUMFB-77, and AAUEB-59 generated the highest chitinase (EI = 3.41), lipase (EI = 4.45), and protease activities (EI = 5.44) respectively. The pathogenicity study of isolates on whitefly nymphs and adults indicated significant variation (P < 0.05) with mortality ranging from 71.67 to 98.33% and 60 to 100% against Bemisia tabaci and Trialeurodes vaporariorum nymphs respectively. The mortality of adults was between 58 and 94.27% against B. tabaci and 59.03 to 95.37% against T.vaporariorum. The result also showed that AAUMB-29, AAUMFB-77, and AAUDM-43 were the most virulent with LC50 values of 2.7 × 104, 5.3 × 104, and 5.4 × 104 conidia/ml against nymphs of B. tabaci, and with LC50 values 6.8 × 104, 8.2 × 104, and 7.2 × 104 conidia/ml against nymphs of T. vaporariorum, respectively. The B. bassiana AAUMB-29, B. bassiana AAUMFB-77, and M. anisopliae AAUDM-43 induced the highest whitefly mortality than other isolates. These isolates can be recommended for further tests under field conditions to fully realize their potential as effective biocontrol agents against whitefly pests in tomato.
Faba bean (Vicia faba L.) is one of the most widely cultivated leguminous crops grown in the Highlands of Ethiopian. This study was aimed at evaluating the effect of Rhizobium leguminosarum bv.viciae isolates from other cross-inoculation hosts from field pea, grass pea, and lentil on faba bean varieties. Thus, 12 isolates were selected from faba bean, field pea, grass pea and lentil using host trap method on soil samples that was collected from North Shoa. All isolates were tolerated to pH (5 to 9), salt concentration (1 to 2%), and at a temperature of (15 to 35°C). Cross-inoculation experiments were conducted in the greenhouse to test the effects of R. leguminosarum isolates from faba bean, field pea, grass pea and lentil hosts on Hachallu and Wolki varieties of faba bean. The mean nodule number, nodule dry weight and mean shoot dry weight of the inoculated plants showed variations among the different cross inoculants (p<0.01). Symbiotic effectiveness varied from a minimum of 64% on Hachallu variety inoculated by isolate AUFBR5 (faba bean) and 52% on Wolki variety by isolate AUFPR1 (field pea) association to a maximum of 98% in Hachallu variety inoculated with isolate AUGPR13 (grass pea), and 117% in Wolki variety inoculated with isolate AUFBR5 (faba bean). The study showed physiological and symbiotic diversity of R. leguminosarum isolates of faba bean, field pea, grass pea and lentil. The effective isolates that have been tested with Hachallu and Wolki varities at green house level should be re-tested under field conditions to ascertain their performance in vivo.
Whiteflies are one of the most devastating horticultural pests attacking tomatoes. Although there are several control methods for the control of whitefly pests, the integrated application of entomopathogenic fungi (IPM) with chemical and botanical insecticides has proven more effective than individual control agents. This study was carried out to evaluate individual and combined treatments of entomopathogens B. bassiana, M. anisopliae, B. thuringiensis, Hunter 40 EC, and neem oil for the control of whitefly species on tomato (Solanum lycopersicum) under greenhouse and field condition. The greenhouse study showed that the different treatments resulted in a 58.48 to 100% reduction of nymphs and a 52.06 to 100% reduction of adults on both Galilea and Melkashola tomato varieties under greenhouse conditions. The combined treatments of AAUMB-29 + Neem oil displayed a higher yield (423.3 g fruits/plant) on the Gelilea tomato variety, and AAUDM-43 + Hunter 40 EC displayed a yield of (376.66 g/plant) on the Melkashola tomato variety. Under field conditions, the application of AAUMB-29 + Hunter 40 EC + Neem oil significantly decreased the whitefly population by 91.93% ( P < 0.001 ) after 10 days of the fourth spray. The result of fruit yield of tomato was significantly higher in all treatments (31.17 t to 70.42 t·ha−1) compared to untreated control (25.83 t·ha−1). Among the treatments, AAUMB-29 + Hunter 40 EC + Neem oil gave the highest fruit yield of 70.42 t·ha−1 followed by AAUMB-29 + Hunter 40 EC (64.50 t·ha−1) on the Galilea tomato variety under field conditions. The combined treatment of AAUMB-29 + Hunter 40 EC + Neem oil was the most effective with lower whitefly infestation, higher marketable yields, and less percentage of yield losses. Further investigations are required to determine the optimization and practicability of this integrated application of treatments for the control of both sucking and chewing insect pests under field conditions.
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