Browsing by Subject "Biocontrol"

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Banana weevil borer (Cosmopolites sordidus) : plant defense responses and control options
(2021) Bakaze, Elyeza; Wünsche, Jens Norbert
Each year 25-75% of banana yields are lost to Cosmopolites sordidus, one of the major pests of banana/plantain plants. This loss is common with resource-limited farmers who cannot afford the frequent application of insecticides due to their cost and developed resistance by weevils. Larvae, the most destructive life stage, occupy ecologically different microenvironments from adult weevils, thus least affected by synthetic insecticides. Feeding of larvae on banana rhizomes interferes with the established and emerging roots which reduce water and nutrient uptake and consequently weaken the plant stability during windy weather. Integrated pest management (IPM) is being promoted, for a single control strategy produces limited and or unsustainable results. IPM options for banana weevils include habitat management (cultural control), biological control, host resistance, botanical control and chemical control as last resort. Of the above IPM strategies, this research evaluated host resistance, botanical plant extracts and entomogenous fungi to contribute to the overall goal of reducing synthetic insecticides use. In the evaluation of host resistance, physiochemical of phenolic origin; lignin, and suberin were considered. Comparably, weevil and methyl jasmonate treatment, induced higher deposits of lignin and suberin, cellular modifications, and high total phenolic content as well as antioxidant capacity in “Km5” than “Mbwazirume” banana cultivars. Induced polyphenols reduced weevil damage to less than 5% in “Km5” compared to 11% damage in the “Mbwazirume” cultivar. However, with the onetime application of 0.01% methyl jasmonate, “Mbwazirume”, had 50% reduced weevil damage compared to untreated control. Extracts from dried clove buds (Syzygium aromaticum), pepper fruits (Piper guineense) and neem seeds (Azadirachta indica) and their synthetic analogs were evaluated as botanical control option to Carbofuran against C. sordidus in the laboratory and infested field experiments. Efficacy of plant extracts and their synthetic analogs, revealed egg hatch inhibitory effect, larvicidal toxicity and adult repellency variation. For instance, clove extracts and its synthetic analogs had the lower egg inhibitory dose (ID50) of 0.08 to 0.22% than black pepper (0.24 to 0.75%), and half the ID50 value caused 50% larvae mortality. However, in 6 to 48 hours pepper repelled 80 - 98%, clove 78 - 90% and neem 63 - 75% adult weevils, an effect that significantly (P =0.001) reduced field weevil population. Lastly, three Entomogenous fungi; Curvularia senegalensis, Fusarium verticillioides, and Fusarium oxysporum species complex (FOSC) were also evaluated for their ability to infect weevil eggs, larvae and adult weevils, and to reduce weevil damage in potted plants. C. senegalensis and F. verticillioides greatly affected egg hatching and larval survival, for instance, they caused 75 to 90% eggs hatch inhibition, unlike the 25 to 55% egg hatch inhibition for Beauveria bassiana and FOSC. Besides that, fungal treated plants 14 days before weevils, had significantly high SPAD value (P <0.0001), less than 20% rhizome damage and predictive weevil mortality R2 = 0.46. Rhizome damage was greatly reduced by C. senegalensis, followed by B. bassiana and F. verticillioides, and it is the first record to demonstrate that C. senegalensis and F. verticillioides are pathogenic to C. sordidus. In conclusion, an IPM that combines host resistance with locally available botanic extracts and effective entomogenous fungi may provide a sustainable intervention in the management of the weevil population and their damages to benefit both commercial and resource-limited farmers.
Characterization ofantifungal properties of lipopeptide-producing Bacillus velezensis strains and their proteome-based response to the phytopathogens, Diaporthe spp
(2023) Akintayo, Stephen Olusanmi; Hosseini, Behnoush; Vahidinasab, Maliheh; Messmer, Marc; Pfannstiel, Jens; Bertsche, Ute; Hubel, Philipp; Henkel, Marius; Hausmann, Rudolf; Vögele, Ralf; Lilge, Lars
Introduction: B. velezensis strains are of interest in agricultural applications due to their beneficial interactions with plants, notable through their antimicrobial activity. The biocontrol ability of two new lipopeptides-producing B. velezensis strains ES1-02 and EFSO2-04, against fungal phytopathogens of Diaporthe spp., was evaluated and compared with reference strains QST713 and FZB42. All strains were found to be effective against the plant pathogens, with the new strains showing comparable antifungal activity to QST713 and slightly lower activity than FZB42. Methods: Lipopeptides and their isoforms were identified by high-performance thin-layer chromatography (HPTLC) and mass spectrometric measurements. The associated antifungal influences were determined in direct in vitro antagonistic dual culture assays, and the inhibitory growth effects on Diaporthe spp. as representatives of phytopathogenic fungi were determined. The effects on bacterial physiology of selected B. velezensis strains were analyzed by mass spectrometric proteomic analyses using nano-LC-MS/MS. Results and Discussion: Lipopeptide production analysis revealed that all strains produced surfactin, and one lipopeptide of the iturin family, including bacillomycin L by ES1-02 and EFSO2-04, while QST713 and FZB42 produced iturin A and bacillomycin D, respectively. Fengycin production was however only detected in the reference strains. As a result of co-incubation of strain ES1-02 with the antagonistic phytopathogen D. longicolla, an increase in surfactin production of up to 10-fold was observed, making stress induction due to competitors an attractive strategy for surfactin bioproduction. An associated global proteome analysis showed a more detailed overview about the adaptation and response mechanisms of B. velezensis, including an increased abundance of proteins associated with the biosynthesis of antimicrobial compounds. Furthermore, higher abundance was determined for proteins associated with oxidative, nitrosative, and general stress response. In contrast, proteins involved in phosphate uptake, amino acid transport, and translation were decreased in abundance. Altogether, this study provides new insights into the physiological adaptation of lipopeptide-producing B. velezensis strains, which show the potential for use as biocontrol agents with respect to phytopathogenic fungi.
Impacts of the fungal bio-control agent Fusarium oxysporum f.sp. strigae on plant beneficial microbial communities in the maize rhizosphere
(2016) Musyoki, Mary Kamaa; Cadisch, Georg
Striga hermonthica causes severe yield reduction in cereal crop production in Sub-Saharan Africa. Intergrated Striga management has been proposed as one of the best options to control striga. Along this line, the use of biocontrol agent (BCA) Fusarium oxysporum f.sp. strigae (Foxy-2) has been proven as an effective and environmental friendly management strategy. It is well established that a prerequisite for a successful BCA is sufficient risk assessment analysis. Towards this direction, Foxy-2 was assessed for its potential non-target impacts on the abundance, community structure of bacterial and archaeal nitrifying prokaryotes as well as enzymatic activities of proteolytic bacteria. Maize rhizosphere soils treated with or without Foxy-2, Striga and high quality organic residues (i.e., Tithonia diversifolia) as N source were evaluated by quantitative polymerase chain reaction (qPCR) and terminal restriction fragment length polymorphism (TRFLP). It was observed that Foxy-2 had a promoting effect on archaeal abundance under controlled conditions in sandy soils. Furthermore, crop growth stage, seasonality and soil type had a strong effect on abundance and community structure of nitrifying prokaryotes over Foxy-2 inoculation. In addition proteolytic enzymatic activities analysis showed that Foxy-2 did not affect their activities. Correlation analysis also showed that abundance and community structure on nitrifying communities positively correlated with extractable organic carbon, extractable organic nitrogen and soil pH, while proteolytic enzymatic activities correlated with extractable organic nitrogen and soil ammonium. It was concluded that Foxy-2 is compatible with nitrifying prokaryotes and proteolytic enzymatic activities.
Investigating the mode of action of the mycoherbicide component Fusarium oxysporum f.sp. strigae on Striga parasitizing sorghum and its implication for Striga control in Africa
(2011) Ndambi Beninweck, Endah; Cadisch, Georg
Amongst the factors that are a threat to food security in Africa, is the parasitic weed Striga hermonthica which affects mostly cereals that constitute the staple food for subsistence farmers, thus affecting the livelihood of millions of people. Popularly known as witchweed, attack due to S. hermonthica can completely destroy the yield of cereal crops. Efforts to combat Striga have had very limited success since farmers rarely adopt control methods due to the mismatch between technologies and farmers? socio-economic conditions. Being such a severe problem, an appropriated method for Striga management adapted for African farmers is very much needed. The use of soil-borne fungi for biocontrol is now being developed as an alternative to the use of chemicals considering the specificity of such fungi and the fact that most of the damage by Striga is done before its emergence. The fungus Fusarium oxysporum f.sp. strigae has been identified and shown to be effective and specific to S. hermonthica and S. asiatica but its mode of action is not yet well known. It is required that the mechanisms underlying the mycoparasitic process of this natural antagonistic agent be well understood before its use. Thus, studies on the effectiveness, specificity and timely colonization of Foxy 2 on S. hermonthica are necessary as well as studies on the effect of Foxy 2 in Striga-host plants which should demonstrate its non-pathogenicity to food crops. The objective of this study was therefore to investigate the mode of action of Foxy 2 in its target S. hermonthica and non-target Sorghum bicolor and also to examine the safety of the use of this mycoherbicide by evaluating its ability to produce toxins. In the first part of the thesis, the ability of Foxy 2 to colonize sorghum roots and possibly shoots was investigated using light and transmission electron microscopy. The efficacy of Foxy 2 to cause death of S. hermonthica seedlings attached to Foxy 2 colonized sorghum roots was also evaluated. Microscopic investigations revealed that the intensity of root colonization by Foxy 2 increased with time and Foxy 2 could survive and colonize the sorghum rhizodermis, root hairs and cortical parenchyma up to four weeks after sowing. This behaviour is well adapted for Striga control as it corresponds to the peak of Striga seedling attachment. Hyphae were completely absent from the sorghum root central cylinder even after four weeks and also absent from the sorghum shoots up to 11 weeks after sowing indicating the non-pathogenity of Foxy 2 to sorghum. Furthermore, Foxy 2 was effective in controlling S. hermonthica by causing disease in 95% and 86% of S. hermonthica seedlings when coated on seeds of tolerant and susceptible sorghum cultivars respectively. Therefore, Foxy 2 could be combined with the tolerant sorghum variety in an integrated approach against S. hermonthica and S. asiatica. The effect of Foxy 2 on various growth stages of S. hermonthica was investigated subsequently so as to understand the mechanisms of action of Foxy 2 within S. hermonthica in the real living complex between the mycoherbicide Foxy 2, the parasite S. hermonthica and its host sorghum. Light, scanning and transmission electron microscopy were used to evaluate the pattern of colonization and control of S. hermonthica seedlings and shoots by Foxy 2. Results showed that 26 days after sowing Foxy 2 coated sorghum seeds, all tissues of the young S. hermonthica seedlings attached to sorghum roots were completely degraded and destroyed by Foxy 2 including the haustorial intrusive cells, hyaline tissue, vessels, central xylem elements and Striga cortical parenchyma. Some S. hermonthica plants which attached to areas of the sorghum root which were not yet colonized by Foxy 2 (towards the root tips), were able to outgrow the fungus and emerged. In the emerged S. hermonthica shoots, hyphae had subsequently penetrated and colonized vessels clogging them over long distances and were identified up to the top of the plants. In some vessels there was an intensive blockage of the vessels by hyphae such that spaces or gaps were rare. Ultrathin sections showed that the diseased S. hermonthica shoots reacted to Foxy 2 invasion by forming an electron dense wall coating along the secondary vessel walls probably to prevent fungal digestion of the walls. The study thus identified two mechanisms by which Foxy 2 contributed to wilting and death of S. hermonthica which included complete digestion of underground S. hermonthica seedlings and hyphal clogging of vessels in emerged S. hermonthica plants which interfered with water conduction. In order to understand the reactions of sorghum towards the presence of Foxy 2 as part of the risk assessment to ensure the safe use of this biocontrol agent, the action of Foxy 2 and a known pathogenic Fusarium species, F. proliferation, were compared in the fourth chapter. Sorghum roots were also wounded to expose the vascular system so as to investigate whether removal of the endodermal barrier could give access to Foxy 2 into the vessels which could lead to digestion resulting in wilting of the sorghum plants. The colonization processes of the two Fusaria species were quite different at all stages of growth. While F. proliferatum degraded the endodermis, invaded the central cylinder and digested the xylem parenchyma two weeks after sowing, Foxy 2 was restricted to the cortex even up to four weeks after sowing. Hyphae of Foxy 2 filled the intercellular spaces at the outer endodermal wall but could not penetrate the endodermis. Sorghum roots were observed to react to Foxy 2 invasion by reinforcing the central cylinder as seen by an increase in blue auto fluorescence especially of the endodermis. Five days after wounding and inoculating sorghum roots, Foxy 2 hyphae invaded the central cylinder very close to the cut but were completely absent from the central cylinder at a distance of 3000 µm from the cut, meanwhile F. proliferatum hyphae had digested the cells of the central cylinder at this distance. This indicated that not only the endodermis was a barrier but there could also be a physiological barrier within the central cylinder of the sorghum root which did not allow further spread of Foxy 2. Hence, exposure of the vascular system did not serve as a route for the invasion of Foxy 2 which therefore implied that it could not cause wilting of the plant. In the last part of the thesis, S. hermonthica shoots were analyzed by HPLC-MS/MS to investigate the possible production of toxins by Foxy 2 to kill the plant. Amongst the toxins tested (beauvericin, fumonisins B1, B2, B3, C and P series, enniatins A, A1, B and B1, and moniliformin), only beauvericin (BEA) was detected to be produced by Foxy 2 in S. hermonthica shoots. The concentration of this toxin increased with increased infection e.g. 60 µg BEA/kg Striga shoot tissue (dry weight) were detected three weeks after emergence rising to 720 µg BEA/kg Striga shoot tissue after six weeks in the severely diseased S. hermonthica shoots. When beauvericin was applied on S. hermonthica shoots at concentrations of 50 µM, transmission electron microscopy showed that all cell types became necrotic. However, beauvericin as well as all the other toxins were not detected in sorghum grains harvested from sorghum plants which were hosts to the S. hermonthica plants and growing from Foxy 2 coated sorghum seeds. Given that some F. oxysporum strains were previously shown to be able to produce fumonisins which are among the toxins which have been reported to be of potential risks to human and animal health, a pure culture of Foxy 2 was evaluated for its fumonisin production ability. Results from real-time PCR using two specific primer pairs for the FUM1 gene (which is the key gene for fumonisin synthesis), were negative confirming that Foxy 2 was not able to produce fumonisins and might not be of major concern for human and animal health when used as a biocontrol agent in the field, therefore safe for use as a biocontrol agent. To conclude, Foxy 2 showed potential to control S. hermonthica by completely destroying young underground stages and clogging vessels in aboveground stages, as well as producing the toxin beauvericin, both actions contributing to wilting of the plants. Its non-pathogenicity to sorghum and its inability to produce fumonisins could be seen as factors which make it well suited as a biocontrol agent. Further research needs to be done to evaluate its efficacy under field conditions and the impact of naturally occurring soil microorganisms and abiotic conditions on performance of Foxy 2 so as to understand its interactions with the environment and to optimize its efficacy.
New approaches to manage Asian soybean rust (Phakopsora pachyrhizi) using Trichoderma spp. or their antifungal secondary metabolites
(2022) El-Hasan, Abbas; Walker, Frank; Klaiber, Iris; Schöne, Jochen; Pfannstiel, Jens; Voegele, Ralf T.
Attempts have been made to determine the in vitro and in planta suppressive potential of particular Trichoderma strains (T16 and T23) and their secondary metabolites (SMs) against Asian soybean rust (ASR) incited by Phakopsora pachyrhizi. Aside from the previously identified SMs 6-pentyl-α-pyrone (6PAP) and viridiofungin A (VFA), the chemical structures of harzianic acid (HA), iso-harzianic acid (iso-HA), and harzianolide (HZL) were characterized in this study. Our results indicate that exposure of urediospores to 200 ppm 6PAP completely inhibits germination. A slightly higher dosage (250 ppm) of HZL and VFA reduces germination by 53.7% and 44%, respectively. Germ tube elongation seems more sensitive to 6PAP than urediospore germination. On detached leaves, application of conidia of T16 and T23 results in 81.4% and 74.3% protection, respectively. Likewise, 200 ppm 6PAP recorded the highest ASR suppression (98%), followed by HZL (78%) and HA (69%). Treatment of undetached leaves with 6PAP, HA, or HZL reduces ASR severity by 84.2%, 65.8%, and 50.4%, respectively. Disease reduction on the next, untreated trifoliate by T23 (53%), T16 (41%), HZL (42%), and 6PAP (32%) suggests a translocation or systemic activity of the SMs and their producers. To our knowledge, this study provides the first proof for controlling ASR using antifungal SMs of Trichoderma. Our findings strongly recommend the integration of these innovative metabolites, particularly 6PAP and/or their producers in ASR management strategies.
Spent Pleurotus ostreatus substrate has potential for managing Fusarium wilt of banana
(2021) Ocimati, Walter; Were, Evans; Tazuba, Anthony Fredrick; Dita, Miguel; Zheng, Si-Jun; Blomme, Guy
A range of basidiomycetes including the edible mushroom Pleurotus ostreatus (Po) can suppress plant pathogens such as Fusarium spp. With the current increase in production and consumption of Po in Uganda, the spent Po substrate (SPoS) could be an alternative to manage Fusarium wilt of banana (FWB), caused by the soil borne pathogen Fusarium oxysporum f. sp. cubense, race 1 (Foc). This study determined the potential of SPoS to inhibit Foc in vitro and in potted plants. In vitro studies confirmed suppression of Foc in pure co-culture (Po vs. Foc) assays and media amended with different concentrations (0% to 50% w/v) of un-sterilized SPoS filtrates. Foc growth in the sterile SPoS filtrate was comparable to the water control, suggesting possible roles of biotic or thermolabile components of the SPoS. To further verify the suppressive effects of SPoS, pot experiments were carried out with a resistant (‘Mbwazirume’, AAA) and susceptible (‘Sukali Ndizi’, AAB) banana cultivar using both artificially and naturally infested soils. Independent of the inoculation method, SPoS significantly reduced the severity of FWB in pot experiments. Susceptible cultivar ‘Sukali Ndizi’ growing in substrates amended with SPoS showed lower (1.25) corm damage (Scale 0–5) than the un-amended control (3.75). No corm damage was observed in uninoculated controls. The resistant cultivar ‘Mbwazirume’, showed slight (0.25) corm damage only in the Foc-inoculated plants without SPoS. These findings suggest that SPoS could be used as part of the management practices to reduce the impact of FWB.