Spodoptera litura is a serious pest to vegetables such as broccoli, beans, cabbage, and dasheen.
Spodoptera litura nucleopolyhedrovirus (SpliNPV) has been studied extensively to determine its infectivity levels, mass production potential, and biosafety towards bees, fish, silkworm, mice, rabbits, and monkeys.
Since 1997, SpliNPV has been produced as a commercialized insecticide via continuous rearing of the host larvae on an artificial diet.
Increasing public concern about the environmental consequences of the massive use of chemical pesticides and the development of resistances to these products by insects have increased scientists’ interest in finding alternatives for controlling insect pests.
Insects are major pests, not only to agricultural crops but also to domestic animals and humans.
Viruses offer alternatives for safe and environmentally friendly insect pest control, using various strategies. Insect viruses have been used as biological control agents with success against various insect pests.
Virus diseases have been reported from more than 800 species of insects and mites. Isolates of the baculovirus and cytoplasmic polyhedrosis virus groups have biological properties which should lead to their successful use as microbial control agents in integrated pest management programmes.
These viruses infect the larval stages of many lepidopterous and hymenopterous pests, producing a chronic or lethal infection and the release of large quantities of relatively stable infective inclusion bodies (IBs).
The IBs serve as the means by which the viruses are transmitted and persist outside the host.
Younger larvae are more susceptible to infection than older stages, and this difference influences the timing of application and doses of virus needed for practical pest control.
The fungicidal activity makes Trichoderma viride useful as a biological control against plant pathogenic fungi. It has been shown to provide protection against such pathogens as Rhizoctonia, Pythium and even Armillaria.
Trichoderma viride is found naturally in soil and is effective as a seed dressing in the control of seed and soil-borne diseases including Rhizoctonia solani, Macrophomina phaseolina and Fusarium species.
When Trichoderma viride is applied at the same time as the seed, it colonizes the seed surface and kills not only the pathogens present on the cuticle, but also provides protection against soil-borne pathogens.
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.
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
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