The mycelium of Trichoderma viride can produce a variety of enzymes, including cellulases and chitinases which can degrade cellulose and chitin respectively.
The mould can grow directly on wood, which is mostly composed of cellulose, and on fungi, the cell walls of which are mainly composed of chitin.
Trichoderma viride is a fungus and a biofungicide.
It is used for seed- and soil treatment for suppression of various diseases caused by fungal pathogens.
Bacillus, (genus Bacillus), any of a genus of rod-shaped, gram-positive, aerobic or (under some conditions) anaerobic bacteria widely found in soil and water. The term bacillus has been applied in a general sense to all cylindrical or rodlike bacteria.
The largest known Bacillus species, B. megaterium, is about 1.5 μm (micrometres; 1 μm = 10−6 m) across by 4 μm long. Bacillus frequently occur in chains.
Unlike most insecticides, which target a broad spectrum of species, including both pests and beneficial insects, Bacillus thuringiensis (Bt) is toxic to a narrow range of insects. Research suggests that Bt does not harm the natural enemies of insects, nor does it impair honeybees and other pollinators critical to agroecological systems. Bacillus thuringiensis (Bt) integrates well with other natural controls and is used for integrated pest management by many organic farmers.
The use of insect-resistant Bacillus thuringiensis (Bt) plants can potentially reduce use of chemical insecticide sprays, which are extremely toxic and expensive. Applications of conventional pesticides recommended for control of the European corn borer, for example, dropped by about one-third after Bt corn was introduced.
Although lethal to certain insect species, Bacillus thuringiensis (Bt) toxin applied as an insecticide or consumed with GMO food crops is considered nontoxic to humans and other mammals because they lack the digestive enzymes needed to activate the Bacillus thuringiensis (Bt) protein crystals. However, any introduction of new genetic material is potentially a source for allergens, and, for this reason, certain strains of Bt are not approved for human consumption.
Bacillus thuringiensis (Bt), soil-dwelling bacterium that naturally produces a toxin that is fatal to certain herbivorous insects. The toxin produced by Bacillus thuringiensis (Bt) has been used as an insecticide spray since the 1920s and is commonly used in organic farming.
Bacillus thuringiensis (Bt) is also the source of the genes used to genetically modify a number of food crops so that they produce the toxin on their own to deter various insect pests.
The toxin is lethal to several orders of insects, including Lepidoptera (butterflies, moths, and skippers), Diptera (flies), and Coleoptera (beetles), though a number of Bt strains are available to make its use more target-specific.
Bacillus mucilaginosus shows potential as a fertilizer that people could use for crops to produce food and other plant-based goods.
It aids in plant growth by solubilizing phosphorus and potassium, both macronutrients required by plants for growth.
It releases these nutrients from soil minerals such as feldspar and mica into soluble forms that plants can uptake.
Crops grown in soils with Bacillus mucilaginosus have greater potassium and phosphorus uptake and more biomass than crops grown without this microbe.
It is also useful for cleaning up waste. It plays a part in microbial flocculation in wastewater by aggregating bacteria and minerals into large clumps that can be more easily removed from liquids such as sewage and industrial wastewater.
Potassium (K) is one of the major macronutrients and plays an important role in plant growth promotion. Potassium deficiency causes chlorosis, leaf falling, slow growth rate, poor root development, reduced production of seeds, and reduced yield in plants. Therefore it is necessary to apply an alternate potassium source such as bioformulations containing potassium solubilizers for improved plant growth and sustainability in agricultural crops (Prasad et al., 2019). Potassium mainly exists in three forms including soil minerals, nonexchangeable, and available form. About 90%–98% of the total K exists as insoluble rock and silicate minerals, micas, or feldspars in the rooting zone, which is relatively unavailable for plant uptake (Scheffer, 2002). The nonexchangeable form of K constitutes 10% of total K and exists as reserve to manage loss from the soil. Only 1%–2% of total K is available and found either in the solution or as part of the exchangeable cation on clay mineral. Further constraints such as imbalanced fertilizers, intensive cropping, soil erosion, leaching, and introduction of hybrids and other high-yielding crop varieties also cause difficulties to the plants. Different species of bacteria Bacillus subtilis, Bacillus mucilaginosus, Bacillus edaphicus, Bacillus circulans, Burkholderia spp, Paenibacillus spp., and Pseudomonas spp. are able to solubilize potassium by producing enzymes and organic acids (Saha et al., 2016; Liu et al., 2012; Hafeez and Hassan, 2011; Basak and Biswas, 2009). Other microbes including fungi, arbuscular mycorrhiza, and yeast also solubilize complex K sources including illite, micas, and orthoclase into soluble forms with the production of organic acid (Zeng et al., 2012). Members of fungi including Aspergillus terreus, Aspergillus niger, Glomas mosseae, Glomas intraradices, and Penicillium sp. have been reported promising in solubilizing complex sources of K (Rajawat et al., 2016; Meena et al., 2015; Lian et al., 2002).
These microbes adopt different approaches including direct and indirect mechanism, polysaccharide secretion, and biofilm formation on mineral surfaces to solubilize complex forms of K into simple ions. A direct method of solubilization is accomplished by the production of organic acids like oxalic, tartaric and citric acids, acidolysis, and enhanced solubility of minerals in the rhizosphere and chemical weathering based on carbonic acid (Mendes et al., 2013; Gerke, 1992; Park et al., 2009; Gadd, 2007). An indirect method of K solubilization includes chelation of the cations, followed by exchange and solubilization on mineral surfaces, formation of metal-ligand complexes, and release of plant hormones (Uroz et al., 2009; Sattar et al., 2019).
In addition to direct and indirect methods, beneficial microbes also adopt K solubilization by releasing exopolysaccharides (EPS), which helps in adhering of microbes over the surface of minerals to enhance the production of organic acids (Liu et al., 2012). These EPS are biodegradable, high-molecular-weight polymers made up of monosaccharides, and play an important role in aggregating soil particles, maintaining water potential, ensuring strict contact with bacteria and roots of plant, and protecting against phytopathogens (Pawar et al., 2016). EPS also adsorb organic acids, maintain the equilibrium between soil and minerals, and enhance dissolution and release of K+ (Lian et al., 2002). Bacteria including Bacillus, Clostridium, and Thiobacillus secrete capsules made of polysaccharides for degrading feldspar and illite to release K+ (Sheng and He, 2006).
Another important approach to solubilize K is the formation of biofilms. Bacteria produce biofilms to adhere to the surfaces of minerals and release various metabolites and organic acids, which lower the pH and help in solubilization of complex minerals and facilitate uptake by plants. The biofilms also help to protect, to adapt, and to survive in extremities of the environment by extracting nutrients through the release of extracellular polymers, polysaccharides exudates, and enzymes and mobilization and weathering of complex minerals.
by Richa Salwan, Vivek Sharma, in Plant Nutrition and Food Security in the Era of Climate Change, 2022
Phthorimaea absoluta is an invasive pest and a major threat to tomato production in sub-Saharan Africa, including Tanzania. Although chemical pesticides are commercially available and used locally, mis- and overuse can cause detrimental effects on human and environmental health, and can lead to emergence of resistance among populations of P. absoluta within a short period, increasing production costs among smallholder farmers in Tanzania.
The effectiveness of alternative options, such as the use of biological control agents and pheromone traps, has not yet been studied in the field in sub-Saharan Africa.
The present study evaluated the effectiveness of a commercially available biopesticide based on Metarhizium anisopliae and pheromone traps for managing P. absoluta in field conditions in Tanzania during the dry and wet season, and compared effectiveness with chemical pesticides (a combination of chlorantraniliprole, emamectin benzoate, spinetram and flubendiamide) and untreated plants as a positive and negative control, respectively. The two field experiments were conducted in a randomized complete block design with three replications per treatment.
Two weeks after transplanting, 20 plants were randomly selected from each plot, with the number of fully expanded leaves per plant and mines per plant counted at 7-day intervals until harvest. At harvest, the number and weight of damaged and marketable fruits were recorded, and yield and marketable yield per plot calculated.
The number of leaves per plant (an indicator of P. absoluta infestation) was higher in the wet season than in the dry season. In the wet season, Metarhizium anisopliae-treated plants contained more leaves than plants in control or pheromone-treated plots. The number of P. absoluta mines per plant was higher in the dry season than in the wet season.
In the dry season, the number of mines per plant was higher in control plots than in plots of other treatments.
However, total yield and marketable yield were higher during the dry season than during the wet season. During both seasons, damage was highest and yield lowest in control plots.
During the dry season, total yield and marketable yield did not differ significantly between pesticide-treated and Metarhizium anisopliae-treated plots.
Biological control using Metarhizium anisopliae could be integrated in field management of P. absoluta in tomato in the highlands of Tanzania as well as in other regions of this country and throughout Africa.
By Zekeya, N.; Dubois, T.; Smith, J.; Ramasamy, S.
Laboratory studies indicated that several Asian strains of Beauveria bassiana have potential as biological control agents of the brown planthopper [Nilaparvata lugens], the green leafhopper [Nephotettix sp.] and the whitebacked planthopper [Sogatella furcifera] on rice.
The infection cycle of Beauveria bassiana in invertebrates bodies has been depicted by Mascarin and Jaronski (2016) Asexual spores (conidia) are dispersed by wind, rain splashing or even by arthropod vectors facilitating the fungus to establish infection on susceptible hosts (OrtizUrquiza and Keyhani 2013).
The host infection by the fungus occurs in four steps: adhesion, germination and differentiation, penetration, and dissemination.
It is characterized by recognition and compatibility mechanisms of conidia of the host cuticle cells (Vey et al. 1982 reported by De Kouassi 2001). Conidia (or in some cases blastospores) were attached to insect’s cuticle by electrostatic and chemical forces (Mascarin and Jaronski 2016). Then, through the production of mucilage, they induced epicuticular modification (Wraight and Roberts 1987) leading to conidia germination.
Germination is a process that depends on environmental conditions, host physiology (biochemical composition of the host cuticle) as well. Such conditions can stimulate or inhibit it (Butt et al. 1995; Butt and Beckett 1994; Smith and Grula 1982; St Leger et al. 1989b). When conditions are suitable, conidia or blastospores germination leads to germ tubes formation. In fact, conidia germinate and form a germ tub with rehydration and chemical stimuli (Mascarin and Jaronski 2016). Differentiation is characterized by the appressoria or penetration peg establishment, which serves as inking point, softening the cuticle and promoting penetration. For this purpose, the germ tub may form a specialized structure, namely appressorium (i.e., an enlarged cell expression bearing key hydrolytic cuticle-degrading enzymes) or penetration peg enabling hyphae growth to breach the host integument (De Kouassi 2001; Mascarin and Jaronski 2016). However, appressoria production is highly dependent on nutritional value of the host cuticle (Magalhaes et al. 1988; St Leger et al. 1989a). A nutritious cuticle may stimulate mycelial growth rather than penetration (St Leger et al. 1989a).
From the appressorium or penetration peg and with the hydrolytic action of enzymes (proteases, chitinases, lipases: the most important being proteases), mechanical pressure, and other factors (such as oxalate), the fungus is able to penetrate all cuticle layers until reaching a nutrient-rich environment, i.e. the insect hemolymph.
In the hemolymph, the fungus undergoes a morphogenetic differentiation from filamentous growth to single-celled, yeast-like hyphal bodies or blastospores that strategically exploit nutrients, colonize internal tissues, and disturb the host immune system. During this stage of the infection, the fungus can also secrete toxic metabolites that help to overcome the insect’s immune defense mechanisms for successfully colonization. Some strains produce non-enzymatic toxins such as beauvericin, beauverolides, bassianolides, and isarolides increasing the speed of the infection process (Hajeck and StLeger 1994; Roberts 1981). These events eventually lead to the death of host that became mummified. When the infected insect dies, the fungus produces an antibiotic called “Oosporin” that is used to overcome bacteria competition in insect gut (De Kouassi 2001). Then, B. bassiana hyphae cross the insect integument preferentially at the inter-segmental level and then become cottony white. Finally, conidiophores appear on the mummified cadavers after a few days and bear newly infection conidia (sporulation) for dispersal (passive dissemination).
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