Bio-encapsulation of microbial cells for targeted agricultural delivery

Biofertilizers, namely Rhizobium and biocontrol agents such as Pseudomonas and Trichoderma have been well established in the field of agricultural practices for many decades. Nevertheless, research is still going on in the field of inoculant production to find methods to improve advanced formulation and application in fields. Conventionally used solid and liquid formulations encompass several problems with respect to the low viability of microorganisms during storage and field application. There is also lack of knowledge regarding the best carrier in conventional formulations. Immobilization of microorganisms however improves their shelf-life and field efficacy. In this context, microencapsulation is an advanced technology which has the possibility to overcome the drawbacks of other formulations, results in extended shelf-life, and controlled microbial release from formulations enhancing their application efficacy. This review discusses different microencapsulation technologies including the production strategies and application thereof in agricultural practices.     

Crop rotation and tillage systems as a proactive strategy in the control of peanut fungal soilborne diseases

Soil management practices can affect the population dynamics of soil microbial communities. Cultural practices can be adequately combined to benefit natural populations of microorganisms that may have a role in biological control (actinomycetes, Trichoderma spp., and Gliocladium spp.), thus contributing to the management of peanut fungal soilborne diseases in a sustainable manner within ecological boundaries. During six agricultural cycles, rhizosphere soil samples were taken from a field subjected to crop rotation (soybean, peanut, and maize), peanut being under two tillage systems (no till, reduced tillage) with the aim of quantifying populations of soil microorganisms. The incidence of diseases caused by soilborne fungi in peanut was determined at harvest. The highest amount of actinomycetes, Trichoderma spp., and Gliocladium spp. were recorded when maize was the preceding crop. Regarding tillage systems, the populations of the three groups of microorganisms were higher in peanut under no tillage than under reduced tillage. Under these conditions, the lowest incidence of peanut blight (Sclerotinia minor) and root rot (strains of Fusarium solani) was observed, suggesting a possible natural control of peanut soilborne pathogens. The quantification of actinomycetes, Trichoderma spp., and Gliocladium spp. was used as a tool to explore the impacts of different management systems on microbial groups that may be involved in the biological control of soilborne diseases, with the aim of combining those practices that improve native populations of possible beneficial microorganisms. This manipulation can provide sustainable management strategies in the control of soilborne diseases, avoiding the use of artificial inoculations of microorganisms, and reducing agrochemical application.     

Organic fertilizers alter the composition of pathogens and arbuscular mycorrhizal fungi in maize roots

Roots of agricultural crops, including maize, are hosts of different microorganisms, many beneficial, like plant growth and health‐promoting arbuscular mycorrhizal fungi (AMF), as well as pathogens including Pythium, Polymyxa and Microdochium. To improve crop nutrition and health, profound knowledge is required regarding how agricultural practices affect field populations of root‐associated microorganisms. Hence, the objective of this work was to evaluate the effect of crop genotype and organic fertilizers on the plant growth performance of maize and their root‐associated microorganisms. The experiment was conducted as a fully factorial greenhouse pot experiment with maize cultivars (two land races and two hybrids) and organic fertilizers (green manure, cow manure and compost) as the two main factors. Plants were harvested 8 weeks after sowing. In general, the different maize cultivars responded similarly to the applications of the organic fertilizers. Cow manure and compost increased plant growth, whereas green manure had limited effect on plant growth. Root colonization with AMF was reduced by green manure with rape. Infection with the root pathogens Pythium and Polymyxa was reduced by all organic fertilizers, whereas in contrast, infection with Microdochium increased with the majority of the organic fertilizers applied. In conclusion, both maize genotype and organic fertilizers affect the abundance of AMF and root pathogens in maize, which should be considered when developing management strategies of these root‐inhabiting microorganisms.     

Development of a mode of application of bioorganic fertilizer for improving the biocontrol efficacy to <Emphasis Type="Italic">Fusarium</Emphasis> wilt

More effective ways of applying biocontrol products should be developed based both on the characteristics of the biocontrol agents and the normal practices of the agricultural producer. A new system was developed to improve the biocontrol efficacy of Fusarium wilt for watermelon production, and this system was tested in pot and field experiments. Biocontrol was achieved by applying a novel bioorganic fertilizer product (BIO) to Fusarium-infested soil. The best biocontrol was obtained by application of a bioorganic fertilizer, BIO, into soil during the nursery phase of watermelon seedling followed by a second application to Fusarium-infested soil when watermelon seedlings were transplanted. In comparison with the controls, the incidence of the disease was reduced by 60–100% in the pot experiment and by 59–73% in the field experiment when the BIO was applied during the nursery stage. After application of BIO during the nursery stage, the number of colony-forming units of Fusarium oxysporum in rhizospheric soil was significantly (P < 0.05) inhibited compared to the controls. An in vitro experiment showed that the antagonist Paenibacillus polymyxa in the BIO could effectively colonize the rhizosphere of watermelon and proliferate along the extending plant roots. This inhibited growth of Fusarium oxysporum in the rhizosphere of watermelon and protected the watermelon roots from attack by the pathogens. The method used for biocontrol Fusarium wilt disease in watermelon should be a useful strategy to improve field efficacy of other biocontrol agents.     

Control of plant parasitic nematodes with active saponins and biomass from Medicago sativa

Medicago sativa L., alfalfa, is the most known plant species within the Medicago genus. The plant has been extensively studied for its content of saponins, mainly consisting of triterpene glycosides of medicagenic acid, possessing several biological properties including a biocidal activity on different soil microorganisms. Phytoparasitic nematodes are responsible for heavy economic damages to numerous agricultural crops and, due to their large distribution, they are among the most difficult crop pests to control. Attention on environmental safety and human and animal health has led to the progressive dismission of many synthetic formulations for the control of those pests and to the search of alternative strategies, including the use of natural metabolites from plants. Saponins from M. sativa may be good candidates for natural nematicide formulations, as in our in vitro studies the saponin mixtures from M. sativa tissues have been found effective in vitro against the virus-vector nematode Xiphinema index, the root-knot nematode Meloidogyne incognita and the potato cyst parasite, Globodera rostochiensis. A structure–activity relationship among saponins and related prosapogenins and sapogenin, respectively, has also been analyzed. The nematicidal efficacy differed among the three assayed nematode species, G. rostochiensis being the most susceptible to the active compounds from alfalfa. The in vitro results were also confirmed by experiments in potting mixes infested by M. incognita or G. rostochiensis and amended with dry top and root material from M. sativa, and in field trials on M. incognita and carrot cyst nematode Heterodera carotae with M. sativa pelleted meal. All amendments reduced root and soil population densities of target nematode species compared to non-treated and chemical controls, with a general improvement of plant growth and yield performances.     

Two granular formulations of Fusarium oxysporum f.sp. orthoceras to mitigate sunflower broomrape Orobanche cumana

Fusarium oxysporum Schlecht. f.sp. orthoceras (Appel & Wollenw.) Bilai, a potential biocontrol agent against Orobanche cumana Wallr.,was formulated into two granular forms, wheatflour kaolin (`Pesta') granules and sodium alginatepellets. The formulations were compared in terms ofeffectiveness for mitigating O. cumanaparasitism in sunflower and shelf-life forstorage. `Pesta' granules reduced the emergence of O. cumana shoots by 64% while sodium alginatepellets did not reduce the emergence rate but increased thepercentage of diseased O. cumana plants.Calculated efficacy of the application was better for`Pesta' granules. Viability of the formulatedmaterial tested in the laboratory was higher in sodium alginatepellets than in the `Pesta' formulation.However, a loss of virulence after six months of storage wasalso observed in sodium alginate pellets in agreenhouse experiment.     

Production and utilization of Bacillus thuringiensis

Biological insecticide formulations based on the entomogenous bacterium. Bacillus thuringiensis, have begun to be used widely in agriculture. This spore-forming bacillus can be grown in submerged culture and formulated to provide stable agricultural formulations compatible with aerial and ground application systems. The safety of these products to nontarget organisms and man is responsible for the growing interest in their use on a variety of crops including pastures and forests. No longer a laboratory curiosity, B. thuringiensis is an economic alternative to chemical insecticides.     

Efficacy of aqueous and oil formulations of a specific Metarhizium anisopliae isolate against Aphis craccivora Koch, 1854 (Hemiptera: Aphididae) under field conditions

Cowpea (Vigna unguiculata) production is constrained by biotic and abiotic factors, among which Cowpea aphid (Aphis craccivora) is ranked a key insect pest that severely limits its potential for provision of food and nutritional security to millions of people in sub‐Saharan Africa. The use of entomopathogenic fungi for A. craccivora management has been recently demonstrated at laboratory and field levels as alternative to synthetic insecticides, but with low adoption in Africa. This study assessed the efficacy of aqueous and oil formulations of Metarhizium anisopliae ICIPE 62 against A. craccivora under field conditions. Metarhizium anisopliae formulations and a commonly used insecticide Duduthrin^® were applied using knapsack sprayers with target output of 350 L/ha. Data on aphid infestation levels were collected weekly. ICIPE 62 efficacy in inducing mortality was also assessed 24 hr post‐treatment coupled with mycosis test. Further, leaf and grain yields were determined. After six weeks post‐treatment in the wet season, there was no significant reduction in aphid density in fungus‐treated plots compared to control and Duduthrin^®‐treated plots. However, in the dry season six weeks after applying the treatments, oil formulation spray resulted low aphid density compared to control and Duduthrin^®‐treated plots. ICIPE 62 formulations did not negatively affect the natural enemies’ population. Leaf yield from the various treatments did not differ significantly in the wet season, but the two fungal formulations recorded higher yields in dry season compared to other treatments. Grain yields in wet and dry seasons were lower in control and Duduthrin^®‐treated plots compared to both ICIPE 62 formulations. This study showed that both M. anisopliae ICIPE 62 formulations are effective in suppressing A. craccivora population under field conditions without adverse effects on its beneficial insects. The study also revealed that efficacy of fungal‐based biopesticides is highly dependent on environmental conditions.     

Performance of carrot and onion seed primed with beneficial microorganisms in glasshouse and field trials

Beneficial microorganisms (Clonostachys rosea IK726, Pseudomonas chlororaphis MA342, Pseudomonas fluorescens CHA0, Trichoderma harzianum T22 and Trichoderma viride S17a) were successfully applied to carrot and onion seed during a commercial drum priming process. Applied microorganisms were recovered above the target of at least 1 × 10⁵ cfu g⁻¹ seed following subsequent application of pesticides to the seed according to standard commercial practices of film-coating carrot and pelletting onion seed. Two glasshouse experiments consistently showed that priming improved emergence of carrot seed and that C. rosea IK726 further improved emergence time. Priming improved emergence of onion seed in one glasshouse experiment, but had an unexpected negative effect on emergence in the second experiment, possibly due to the proliferation of an unidentified indigenous microorganism during priming, becoming deleterious in high numbers. In this experiment, the application of beneficial microorganisms during priming negated this effect and significantly improved emergence. For each crop, a series of field trials was also carried out over three years, at two different sites each year. Although some positive effects of different seed treatments were seen on emergence or yield in individual field trials, no consistent effects were found for primed or microorganism-treated seed across all sites and years. However, a combined analysis of data for all years and sites indicated that pesticide application did consistently improve emergence and yield for both carrot and onion. This is the first comprehensive study assessing glasshouse and field performance of carrot and onion seed primed with beneficial microorganisms during a commercial process of drum priming in the UK.     

Production of environmentally safe biocides from essential oils having antimicrobial activity

Different liquid formulations of anise, coriander and black cumin essential oils were used for preparing some biocides. The prepared formulations were tested for their antimicrobial activity against some post-harvest pathogenic microorganisms. The tested microorganisms were Fusarium oxysporum (Dray rot of potato), Alternaria alternata (Black rot of tomato), Penicillium italicum, P. digitatum, (Blue and green rot of orange, respectively), Botryitus cinerea (Gray rot of strawberry) and Erwinia carotovora (Soft rot of potato).The results revealed that the different formulations showed a complete inhibition effect on the growth of most of the tested microorganisms. Also, the antimicrobial activity of the formulated essential oils did not affect the formulation process compared with the original oil.     

脱落酸生物合成研究进展

脱落酸作为一种抑制生长的植物激素,是平衡植物内源激素和调节生长代谢的关键因子。脱落酸具有提高作物抗旱耐盐、减少果实褐变的作用,同时可降低疟疾发病率、刺激胰岛素分泌,因此在农业和医药领域有着广阔的应用前景。相较于传统的植物提取法和化学合成法,利用微生物合成脱落酸是一种经济、可持续的来源方式。目前利用天然微生物如灰葡萄孢霉菌、蔷薇色尾孢菌等合成脱落酸的研究已经取得了诸多进展,而脱落酸的异源微生物合成研究相对较少。酿酒酵母、解脂耶氏酵母、大肠杆菌等工程菌株作为天然产物异源合成的常用宿主,具有遗传背景清晰、易于操作、便于工业化生产等优势,因此利用微生物异源合成脱落酸是一种更具潜力的生产方式。本文着重从底盘细胞的选择、关键酶的筛选与表达强化、辅因子的调节、增强前体供应及促进脱落酸外排5个方面对微生物异源合成脱落酸的研究进行综述。最后,对该领域的未来发展方向进行了展望。     

Formulation and Delivery of the Bacterial Antagonist Bacillus subtilis for Management of Lentil Vascular Wilt Caused by Fusarium oxysporum f. sp. lentis

Different formulations of Bacillus subtilis were prepared using standard laboratory protocols. Bacillus subtilis survived in glucose and talc powders at 8.6 and 7.8 log₁₀ CFU/g, respectively, for 1 year of storage at room temperature compared with 3.5 log₁₀ CFU/g on a peat formulation. Glasshouse experiments using soil and seed treatments were conducted to test the efficacy of B. subtilis for protecting lentil against the wilt disease caused by Fusariumoxysporum f. sp. lentis. Seed treatments with formulations of B. subtilis on glucose, talc and peat significantly enhanced its biocontrol activity against Fusarium compared with a treatment in which spores were applied directly to seed. The formulations decreased disease severity by reducing colonization of plants by the pathogen, promoting their growth and increased the dry weight of lentil plants. Of these treatments the glucose and talc‐based powder formulations were more effective than the peat formulation and the spore application without a carrier. It was shown that the B. subtilis spores applied with glucose were viable for longer than those applied with other carriers. Seed treatment with these formulated spores is an effective delivery system that can provide a conducive environment for B. subtilis to suppress vascular wilt disease on lentil and has the potential for utilization in commercial field application.     

Evaluation of seed dressing and soil application formulations of Trichoderma species for integrated management of dry root rot of chickpea

The efficacy of the newly developed seed dressing and soil application formulations of Trichoderma viride, T. virens and T. harzianum were evaluated individually and in combinations under pot and field experiments for the management of dry root rot (Rhizoctonia bataticola) of chickpea (Cicer arientinum). In pot experiments, T. harzianum based seed dressing formulation, Pusa 5SD, and soil application formulations, Pusa Biogranule 5 (PBG 5) and Pusa Biopellet 10G (PBP 10G), were found to be effective in reducing dry root rot incidence in chickpea and increasing the seed germination, shoot and root lengths of the crop. Under field experiments, a combination of soil application of T. harzianum based PBP 10G and seed treatment with Pusa 5SD+carboxin was found to be the best by providing the highest seed germination, shoot and root lengths and grain yield and the lowest dry root rot incidence in chickpea.     

Bio-formulation of fluorescent Pseudomonas spp. induces systemic resistance against red rot disease and enhances commercial sugar yield in sugarcane

Abstract

Isolates of Pseudomonas spp. collected from the rhizosphere of sugarcane and cane stalks were screened for their antagonistic activity against Colletotrichum falcatum causing red rot disease in sugarcane. Talc formulations of the selected Pseudomonas spp. isolates improved the sugarcane vegetative sett germination and sugarcane growth under field conditions. Optimal talc formulations were assessed for their effect on induction of systemic resistance against the pathogen in the canes under artificial inoculation. All the four isolates CHAO, EP1, KKM1 and VPT4 were effective in inducing systemic resistance against C. falcatum in two seasons. In other studies, the bacterial formulations were assessed to induce resistance in sugarcane in a sick plot situation. In pathogen-infested soil the isolates KKM1 and CHAO suppressed the red rot disease development in susceptible sugarcane cultivar. Pseudomonas strains also protected sugarcane in a disease-endemic location. Pseudomonas spp treatment substantially improved the cane juice quality parameters affected by the pathogen infection. Standardization of talc formulations and application methods in the field offers potential for large-scale application of biocontrol formulations for the management of red rot disease in sugarcane growing regions.     

Formulations useful in applying beneficial microorganisms to seeds

Microbial inoculants are very likely to have an increasing role in agriculture as the trend away from chemical treatments for plants continues. For microbial inoculation to be effective, it must be compatible with agricultural needs. This usually means that the microorganisms must be formulated with agents that facilitate packaging, extend shelf-life and render the preparation easy to handle. This article addresses these general points and considers formulations that may be useful in applying beneficial microorganisms to seeds.     

Field efficacy of biorational insecticides against Melanaphis sacchari (Zehntner) in sorghum

Abstract

The sugarcane aphid, Melanaphis sacchari (Zehntner), is a major pest in diverse sorghum-growing regions, affecting yields if no effective control measures are implemented. The objective of this study was to evaluate the field efficacy of commercial formulations of biorational insecticides against this pest. All the evaluated biorational insecticides exerted acceptable biological efficacy for at least 7 days after application. The insecticides based on fatty acid potassium salts (Ultralux^® S and Impide^®) maintained aphid density below the established threshold of 50 aphids per leaf up to 14 days after application. The results obtained suggest that biorational insecticides can be included in the integrated management of M. sacchari.     

Organic agricultural practice enhances arbuscular mycorrhizal symbiosis in correspondence to soil warming and altered precipitation patterns

Climate and agricultural practice interact to influence both crop production and soil microbes in agroecosystems. Here, we carried out a unique experiment in Central Germany to simultaneously investigate the effects of climates (ambient climate vs. future climate expected in 50–70 years), agricultural practices (conventional vs. organic farming), and their interaction on arbuscular mycorrhizal fungi (AMF) inside wheat (Triticum aestivum L.) roots. AMF communities were characterized using Illumina sequencing of 18S rRNA gene amplicons. We showed that climatic conditions and agricultural practices significantly altered total AMF community composition. Conventional farming significantly affected the AMF community and caused a decline in AMF richness. Factors shaping AMF community composition and richness at family level differed greatly among Glomeraceae, Gigasporaceae and Diversisporaceae. An interactive impact of climate and agricultural practices was detected in the community composition of Diversisporaceae. Organic farming mitigated the negative effect of future climate and promoted total AMF and Gigasporaceae richness. AMF richness was significantly linked with nutrient content of wheat grains under both agricultural practices.     

Soil application of Beauveria bassiana GHA against apple sawfly,Hoplocampa testudinea (Hymenoptera: Tenthredinidae): Field mortality and fungal persistence

Low impact alternatives to synthetic insecticides for the control of apple sawfly (Hoplocampa testudinea Klug) are scarce encumbering pest management in organic apple orchards. We investigated the soil persistence and field efficacy of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (BotaniGard) against apple sawfly under common organic orchard practices. We also assessed the efficacy of B. bassiana GHA and Metarhizium brunneum Petch (indigenous strain) against sawfly in the laboratory. Larvae treated with either fungus in the laboratory died faster than control larvae and displayed 49.4%–68.4% mycosis. In the field, B. bassiana density remained high in the week after application, during larval descent to the soil. Fungal density decreased to 25% at 49 d after application and to 0.4% after 55 weeks. Molecular markers revealed that the majority of fungal isolates recovered comprised the applied B. bassiana strain GHA. Larvae pupating in soil cages in the orchard for 49 d displayed 17% mycosis. The high efficacy under laboratory conditions was not seen in the field. B. bassiana application resulted in densities above the upper natural background level during the growing season, but reversion to background levels occurred within a year. It remains to be investigated whether this has a detrimental effect on nontarget organisms. Additional work is needed to bridge the knowledge gap between laboratory and field efficacy in orchards.     

Entomopathogenic Nematode Production and Application Technology

Production and application technology is critical for the success of entomopathogenic nematodes (EPNs) in biological control. Production approaches include in vivo, and in vitro methods (solid or liquid fermentation). For laboratory use and small scale field experiments, in vivo production of EPNs appears to be the appropriate method. In vivo production is also appropriate for niche markets and small growers where a lack of capital, scientific expertise or infrastructure cannot justify large investments into in vitro culture technology. In vitro technology is used when large scale production is needed at reasonable quality and cost. Infective juveniles of entomopathogenic nematodes are usually applied using various spray equipment and standard irrigation systems. Enhanced efficacy in EPN applications can be facilitated through improved delivery mechanisms (e.g., cadaver application) or optimization of spray equipment. Substantial progress has been made in recent years in developing EPN formulations, particularly for above ground applications, e.g., mixing EPNs with surfactants or polymers or with sprayable gels. Bait formulations and insect host cadavers can enhance EPN persistence and reduce the quantity of nematodes required per unit area. This review provides a summary and analysis of factors that affect production and application of EPNs and offers insights for their future in biological insect suppression.     

Stability of biocontrol products carrying Candida sake CPA-1 in starch derivatives as a function of water activity

The preservation and shelf-life of formulations of the biocontrol agent Candida sake CPA-1 and starch derivatives as a function of water activity (a_W) were studied in terms of the physical stability of the products and cell viability. Formulations of biocontrol products (BCPs), based on combinations of potato starch and pre-gelatinised potato starch (F1 and F2) or maltodextrines (MD) (F3) containing cell protectants, were obtained by fluidised-bed drying. The carriers and the formulated products were stored at 20°C under different a_W conditions. The water sorption and water plasticization behaviour of the different products were analysed through the water sorption isotherms and glass transition temperatures (T_g). Likewise, the viability of C. sake over time was determined as a function of the a_W. The solubility of the products was also assessed. Although formulations stored at 20°C and low a_W (≤?0.33) exhibited a better shelf-life, a significant decrease in cell survival ratio after 180 storage days was observed. Cold storage (5°C) was required to better maintain the cell viability, thus prolonging the shelf-life of BCPs. Formulations containing MD were the most effective at preserving cell viability and also exhibited the highest water solubility. All the formulations were physically stable at ambient temperature; therefore, the cell stability is the critical point at which to establish both the a_W levels and temperature during storage. Packaging the product using high water vapour barrier material and under cold storage would be necessary to ensure a high number of viable cells and an effective and competitive BCP.