Virulence and horizontal transmission of Metarhizium anisopliae by the adults of the greenhouse whitefly Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) and the efficacy of oil formulations against its nymphs

The pathogenicity of dry conidia and fungal suspensions of 16 entomopathogenic fungal isolates (10 Metarhizium anisopliae and six Beauveria bassiana) was evaluated against adults and second instar nymphs of the greenhouse whitefly, Trialeurodes vaporariorum respectively. All the tested isolates were pathogenic to T. vaporariorum and caused mortality of 45–93% against the adults and 24–89% against the nymphs. However, M. anisopliae strains showed higher virulence to both developmental stages as compared to B. bassiana strains. The three most virulent isolates that caused high mortalities in adults were M. anisopliae ICIPE 18, ICIPE 62 and ICIPE 69, with cumulative mortalities of 82, 91 and 93%, and median lethal times (LT50) of 5.20, 5.05 and 4.78 days, respectively. These isolates were further assessed for spore acquisition and retention by the adult insects at 0, 24, 48 and 72 h after exposure to dry conidia spores. There was no significant difference among isolates on their acquisition by the insects, although the effect of time on the number of spores retained by each insect was significant. For M. anisopliae ICIPE 62 and ICIPE 69, spore number was significantly higher immediately after exposure at 0 h than at 24, 48 and 72 h, whereas for M. anisopliae ICIPE 18, the spore number remained constant for all the days. The infected “donor” insects were able to horizontally transmit the acquired spores to uninfected “recipient” insects causing high mortality rates in both donor and recipient groups. Metarhizium anisopliae ICIPE 7, ICIPE 18 and ICIPE 62 were the most virulent isolates against the nymphs in aqueous formulation during the first screening with >80% mortality. However, in 2% (v/v) oil formulations at 1 108 conidia/ml, canola formulated ICIPE 62, ICIPE 18 and olive formulated ICIPE 18 were the most effective, resulting in 87.8, 88.1 and 99.4% nymphal mortalities respectively and with lower LT50. Oil formulations significantly enhanced the efficacy and virulence of the isolates against the nymphs compared to aqueous formulations.The German Academic Exchange Service (DAAD) through African Regional Postgraduate Programme in Insect Science (ARPPIS) of icipe. The icipe core funding provided by UK’s Foreign, Commonwealth and Development Office (FCDO); Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya.http://www.cell.com/heliyonam2022Forestry and Agricultural Biotechnology Institute (FABI)Zoology and Entomolog

Efficacy of Metarhizium anisopliae and (E)–2–hexenal combination using autodissemination technology for the management of the adult greenhouse whitefly, Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae

DATA AVAILABILITY STATEMENT : The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding author.The efficiency of an autodissemination technique in controlling adult whiteflies, Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae) on tomato, Solunum lycopersicum was investigated with previously identified potent fungal isolates of Metarhizium anisopliae ICIPE 18, ICIPE 62 and ICIPE 69 under screenhouse or semi-field conditions. The autodissemination device was inoculated with dry conidia of the M. anisopliae isolates, while control insects were exposed to a fungus–free device. Sampling for conidia uptake, conidial viability and persistence, and insect mortality was done at 1, 2, 3, 5 and 8 days post–exposure, and collected insects were monitored for mortality over ten days. Overall, mortality was higher in insects exposed to ICIPE 18 (62.8%) and ICIPE 69 (61.8%) than in those exposed to ICIPE 62 (42.6%), with median lethal times, (LT50) ranging between 6.73–8.54 days. The control group recorded the lowest mortality rates (18.9%). A general linear reduction in conidial viability with exposure time was observed, although this was more pronounced with M. anisopliae ICIPE 62. Insects exposed to M. anisopliae ICIPE 69 also recorded the highest conidia uptake, hence selected for further evaluation with a T. vaporariorum attractant volatile organic compound, (E)–2–hexenal. The volatile inhibited fungal germination in laboratory compatibility tests, therefore, spatial separation of M. anisopliae ICIPE 69 and (E)–2–hexenal in the autodissemination device was conducted. The inhibitory effects of the volatile were significantly reduced by spatial separation at a distance of 5 cm between the fungus and the volatile, which was found to be more suitable and chosen for the subsequent experiments. Results showed that (E)–2–hexenal did not influence conidia uptake by the insects, while fungal viability and the subsequent mortality variations were more related to duration of exposure. The fungus–volatile compatibility demonstrated with spatial separation provides a basis for the optimisation of the volatile formulation to achieve better T. vaporariorum suppression with an excellent autodissemination efficiency when used in the management of whiteflies under screenhouse conditions.BioInnovate Africa Phase I project “Promoting smallholder access to fungal biopesticides through Public Private Partnerships in East Africa” (BA/CI/ 2017-02/PROSAFE), and UK’s Foreign, Commonwealth and Development Office (FCDO) (FCDO Biopesticide Project, B2291A - FCDO - BIOPESTICIDE) through the International Centre of Insect Physiology and Ecology (icipe). The icipe core funding provided by UK’s Foreign, Commonwealth and Development Office (FCDO); Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya.https://www.frontiersin.org/journals/insect-sciencehj2023Forestry and Agricultural Biotechnology Institute (FABI)Zoology and Entomolog

Endophytic colonisation of Solanum lycopersicum and Phaseolus vulgaris by fungal endophytes promotes seedlings growth and hampers the reproductive traits, development, and survival of the greenhouse whitefly, Trialeurodes vaporariorum

In the scope of mitigating the negative impacts of pesticide use and managing greenhouse whiteflies, Trialeurodes vaporariorum sustainably, 16 endophytic fungal isolates from five different genera (Beauveria, Trichoderma, Hypocrea, Bionectria, and Fusarium) were screened for their ability to colonise two preferred host plant species, namely, tomato (Solanum lycopersicum L.) and French bean (Phaseolus vulgaris L.), through seed inoculation. Seven and nine isolates were endophytic to P. vulgaris and S. lycopersicum, respectively, where significant differences in the endophytic colonisation rates were observed among the fungal isolates in P. vulgaris and its plant parts, with a significant interaction between the isolates and plant parts in S. lycopersicum. Hypocrea lixii F3ST1, Trichoderma asperellum M2RT4, Trichoderma atroviride F5S21, and T. harzianum KF2R41 successfully colonised all the plant parts of both hosts and therefore were selected and further evaluated for their endophytic persistence, effect on plant growth, and pathogenicity to T. vaporariorum adults and F1 progeny. The four endophytes remained in both host plants for the 5-week assessment with varied colonisation rates related to the strong interaction with the time, isolates, and plant parts in both hosts. The effect of the same endophytes on the different host growth parameters varied in P. vulgaris and S. lycopersicum, with T. asperellum M2RT4 not boosting the growth in both host plants while T. atroviride F5S21 resulted in enhanced shoot biomass in S. lycopersicum. T. atroviride F5S21 and T. harzianum KF2R41 inoculated S. lycopersicum plants and H. lixii F3ST1, T. asperellum M2RT4, and T. harzianum KF2R41 inoculated P. vulgaris plants had significantly lower oviposition, while nymph development in both hosts was significantly prolonged in all the endophytically– colonised plants. The endophytes H. lixii F3ST1 and T. asperellum M2RT4 significantly reduced the longevity/survival of the exposed T. vaporariorum adults and the progeny in both S. lycopersicum and P. vulgaris. The findings demonstrate the attributes of the various endophytes in host plant growth promotion as well as their effects on the lifehistory parameters of T. vaporariorum and could consequently be developed as potential endophytic fungal-based biopesticides for the sustainable management of the pest in S. lycopersicum and P. vulgaris cropping systems.This research was funded by the BioInnovate Africa Phase I project “Promoting smallholder access to fungal biopesticides through Public-Private Partnerships in East Africa” (BA/CI/2017- 02/PROSAFE), and the Foreign, Commonwealth, and Development Office of United Kingdom (FCDO) (FCDO Biopesticide Project, B2291A- FCDO -BIOPESTICIDE) through the International Centre of Insect Physiology and Ecology (icipe). We thank the German Academic Exchange Service (DAAD) In-Region Post-graduate Scholarship for the financial assistance provided to VP through African Regional Postgraduate Programme in Insect Science (ARPPIS). We gratefully acknowledge the icipe core funding provided by the Foreign, Commonwealth, and Development Office of United Kingdom (FCDO); Swedish International Development Cooperation Agency (Sida); the Swiss Agency for Development and Cooperation (SDC); the Federal Democratic Republic of Ethiopia; and the Government of the Republic of Kenya.http://www.frontiersin.org/Plant_Scienceam2022Forestry and Agricultural Biotechnology Institute (FABI)Zoology and Entomolog

Identification of soft rot species found in the Harare area of Zimbabwe and an evaluation of the susceptibility of selected potato cultivars of the pathogens

Experiments were conducted at the University of Zimbabwe, Crop Science Department from 2012- 2014 with the overall aim of identifying soft rot pathogens in the peri-urban Harare area and to screen some of the locally grown potato cultivars for resistance to these pathogens. In the first experiment, potato tubers and stems showing soft rot and blackleg symptoms respectively were purposely collected from eight commercial potato farms within a 60 km radius of Harare. Using standard biochemical tests, a polymerase chain reaction and sequencing, the predominant soft rot pathogen in the area was found to be Dickeya species. In experiment II, five potato cultivars namely Amethyst, BP1, Jasper, Montclaire and KY20 were evaluated for their response to blackleg caused by Pectobacterium carotovorum subsp. brasiliensis (Pcb) in a potted experiment. A randomised complete block design with four blocks was used. Six-week old plants were inoculated in the stem with 6x108 cfuml-1Pcb suspension. Data on disease incidence was collected after one week. Analysis of variance on log10 transformed disease incidence data showed no significant differences among cultivars (P>0.05). All the cultivars showed typical blackleg symptoms and were susceptible to blackleg caused by Pcb. The objective of experiment III was to evaluate the biochemical defence mechanisms of the five cultivars by analysing the activities of two defence enzymes, polyphenol oxidase (PPO) and peroxidase (POD) in response to pathogen infection and mechanical damage. The experiment was arranged in a Completely Randomised Design with a 5*6 factorial treatment structure replicated twice. The moderately resistant cultivar Montclaire was used as the control. Six week old plants were stem inoculated with 6 x 108 cfuml- 1Pcb or wounded by cutting off the plant’s apical bud. Enzyme assays were conducted on leaf samples taken at 0, 12, 24, 48, 84 h and one week after treatments. Four leaves from the middle of the plant were excised using the destructive sampling method. Results showed there was no significant difference on PPO and POD activity in inoculated and wounded plants for both seasons (P>0.05). The interaction between time and cultivar had a significant effect on enzyme activity (P<0.05) with differences in POD activity observed at 12, 24 and 84 h at which Montclaire showed the highest enzyme activity, Amethyst, BP1 and Jasper were intermediate with KY20 exhibiting the lowest enzyme activity. For PPO, the interaction between cultivar and time was significant in 2012 only with Montclaire showing a higher activity than the other cultivars at 12, 24 and 84 h. These results suggest that both pathogen infection and mechanical damage can induce PPO and POD although the level of induction depends on other factors such as cultivar and time after treatment. Experiment IV was carried out to find out if foliar sprays of salicylic acid (SA) and acibenzolar-s-methyl (ASM) can cause an induction of PPO and POD. The above mentioned five cultivars were used. The experiment was a Completely Randomised Block Design with a 5*3*3 factorial treatment structure. Replication was done across blocks. In the three treatment groups, four week old plants were sprayed with 1.5 mM SA; 100 mg active ingredient/litre (a.i/l) ASM and water (control) till run-off. Sampling was carried out as in experiment III and assays were done at 0, 3 and 6 days after treatments. Results showed that cultivars had a significant effect on PPO and POD activity (P<0.05). The interaction between treatment and time showed a significant effect on enzyme activity (P<0.05). The control treatment exhibited enzyme activities higher or equal to SA and ASM treatments. Results suggest that 1.5 mM SA and 100 mg a.i/l ASM applied as foliar sprays were not effective in enhancing PPO and POD activity. Control of soft rot pathogens using on-farm cultural practices still remains an effective management strategy to reduce losses from soft rots. Defence enzymes alone were not enough to protect the plants as all the cultivars proved susceptible to blackleg caused by Pcb.With Dickeya species now the predominant soft rot pathogen in the area under study, an understanding of these plant-pathogen systems enables the implementation of appropriate control measures in order to minimise losses.,The Regional Universities Forum for Capacity Building in Agriculture (RUFORUM