What are mushrooms? 1. Zygomycota Most mushrooms belong to the Basidiomycota ,and aid in producing, storing of spores that would be used in reproduction. Mushrooms have been consumed by humans for thousands of years. Since the demand for these mushrooms has increased, commercial mushroom cultivation has started. In Sri Lanka, demand for edible mushrooms has increased in the last few years.
Figure 1 - Labelled figure of mushrooms
Commercially Cultivated Mushrooms in Sri Lanka Among these mushroom types, Muthubeli Bimmal is the most popular Mushroom variety and Piduru Bimmal are commonly cultivated. Edible Mushrooms Native to Sri Lanka Pest and the Disease Management in Mushroom Cultivation Control Methods Preservation of Harvested Mushrooms Characteristics of Poisonous Mushrooms Simple Tricks to Identify the Poisonous Mushrooms at Home
Figure 2 – 𝘈𝘮𝘢𝘯𝘪𝘵𝘢 𝘮𝘶𝘴𝘤𝘢𝘳𝘪𝘢 – a Poisonous Mushroom
Advantages of Mushroom Cultivation
References https://agrislanka.blogspot.com Image courtesy Featured image – https://agri.pdn.ac.lk>dodangolla
Mushrooms are unique structures of fungi that belong to the Kingdom fungi, which also includes yeasts, moulds, and mildews. Fungi have been categorized under four major groups.
2. Ascomycota
3. Basidiomycota
4. Deuteromycota
In Sri Lanka, growing mushrooms is primarily done at the household level as a small business. There are many mushroom growers in Sri Lanka. Even though there is a sizable market for high-quality mushrooms, most growers frequently fall short of the standards because they lack the necessary knowledge. If done properly, mushroom cultivation can be a lucrative business.
Uru Paha Bimmal – Lentinus giganteus
Uru paha Bimmal is a mushroom species native to Sri Lanka. This mushroom species has the taste of Pork. Hence the name Uru (Pig) paha Bimmal. This species is the largest Mushroom in Sri Lanka. Uru paha bimmal grow naturally around the roots of large trees like Jack (Artocarpus heterophyllus). This species has shown promising results of growing under artificial environments. Apart from these varieties, some other types of mushrooms that naturally grow in Sri Lanka include Mawali Hathu, Indalolu, Monara Bimmal, and Kiri Bimmal.
Large-scale financial losses result from pest attacks on the mushroom industry. Particularly harmful insect species include Drosophila, which feeds on these mushrooms. When mushrooms appear transparent or decayed, these pest attacks are apparent.
Once these mushrooms have been infected, it is difficult to control the pests of mushrooms. So, it is really important to take actions to prevent the pest attacks from the beginning of the cultivation. Keeping the equipment used in Mushroom cultivation clean, avoid using same cultivation room to keep differently aged mushrooms, removing and destroying any infected bags from the cultivating area ,harvesting the mushrooms at correct maturity, only using sprayers to moist the cropping room without using hands, if the pest attack is severe, remove all the bags from the cottage and use a recommended insecticide to treat the infected area – keeping the cottage close for 24 hours after treating could be practiced.
As mushrooms contain more than 90% of water, they have less shelf – life. If mushrooms are kept in an open environment, these mushrooms can dry rapidly due to loss of water. This will also result in reduction of weight of mushrooms. So, it is really important to preserve these mushrooms immediately after harvesting.
Muthubeli Bimmal can be kept fresh in a cold place up to 12 hours after the harvest. This can be kept inside a refrigerator, packed in aerated polythene bags up to 2 – 3 days. To keep this species up to 4 -6 weeks, mushrooms can be boiled for three minutes and stored in a deep freezer.
Stripped mushrooms can be boiled with water vapor for 03 minutes and then sun dried to preserve for 06 months.
Piduru Bimmal is less preservable. It can be kept up to several hours after the harvest in a cold environment. Can be kept up to 24 hours in a refrigerator.
Poisonous mushrooms have a dark color and a strong aroma. One of the characteristics of poisonous mushrooms is that they deter insects.
To identify poisonous mushrooms, one can perform easy tests at home. The mushrooms may be poisonous if the onions turn purple when cooked with them or if they stain the silver spoons black.
Good return on investment, availability of low-cost raw material, ability to start the cultivation within a small space, ability to start the cultivation with prevailing infrastructure facilities (Room inside a house), harvesting is possible in short duration of time.
Figure 1 – https://www.researchgate.net/figure.Mushroom-morphology
Figure 2 – https://en.m.wikipedia.org/wiki/File:Amanita_muscaria
Day: October 27, 2022
Probiotics – Double Edged Sword Effect of a Known Savior
Probiotics are the live beneficial microbes that obtain for desired outcomes, such as prevention of diseased state or improvement in general health outcome observed in host organisms. Probiotics can be either bacteria or fungi. Most probiotic organisms are lactic acid bacteria (LAB), which comprise a wide range of genera and include a considerable number of species, especially Lactobacillus, Bifidobacterium, and Enterococcus species. Probiotic bacteria can be epiphytes, endophytes, or rhizospheric bacteria. There are plant probiotics as well as human or animal probiotics, where animal probiotics are the majority.
Nowadays, there is a trend of using probiotics instead of antibiotics due to their higher safety. But there are certain probiotics that contain antibiotic-resistant genes. The hidden danger in this trend is that the genes that are responsible for antibiotic resistance can be horizontally transferred to other bacterial strains, especially pathogen genomes. Horizontal gene transfer occurs through three main genetic mechanisms: transformation, conjugation, and transduction. Once transferred, the genes and pathogens continue to evolve, often resulting in bacteria with greater resistance.
There have been several clinical incidents, including treatment failures and eventually extending to both hospital morbidities as well as mortalities, caused by pathogens with antibiotic resistant genes. Lactobacillus is a very good example of a probiotic bacteria genus which consists of antibiotic resistant genes. According to recent studies, most of the Lactobacillus strains contain at least 11 tetracycline resistant genes, which were able to transfer horizontally between Lactobacillus strains as well as to different gram-positive bacteria, including pathogens such as Staphylococcus strains. Apart from that, Lactobacillus strains, which are multi-drug resistant mediated, have a high chance of acquiring antibiotic resistance and receiving antibiotic resistant genes from other bacterial strains. This phenomenon can also happen in probiotic strains which have not been studied yet.
Figure 1 – Mechanisms of bacterial horizontal gene transfer
There is no mechanism to eliminate the antibiotic resistance effect of probiotics. But these genes can be screened according to a properly recognized procedure to reduce the effect of antibiotic resistance. This is a crucial safety hurdle that a certain probiotic should pass before being used as a safe probiotic. Educating the public about this double-edged sword effect is a current need for the betterment of the community.
References
Shuhadha, M. F. F., Panagoda, G. J., Madhujith, T., & Jayawardana, N. W. I. A. (2017). Evaluation of probiotic attributes of Lactobacillus sp. isolated from cow and buffalo curd samples collected from Kandy. Ceylon Medical Journal, 62(3).
Ruiza, D., Agaras, B., de Werrab, P., Wall, L. G., & Valverde, C. (2011). Characterization and screening of plant probiotic traits of bacteria isolated from rice seeds cultivated in Argentina. The Journal of Microbiology, 49(6), 902-912.
Burmeister, A. R. (2015). Horizontal gene transfer. Evolution, medicine, and public health, 2015(1), 193.
Gueimonde, M., Sánchez, B., de los Reyes-Gavilán, C. G., & Margolles, A. (2013). Antibiotic resistance in probiotic bacteria. Frontiers in microbiology, 4, 202.
Image courtesy
Featured image – https://theconversation.com/how-to-train-the-bodys-own-cells-to-combat-antibiotic-resistance-106052
Figure 1 – https://www.researchgate.net/publication/361748873/figure/fig4/AS:1184084101472259@1659319057983/Mechanisms-of-horizontal-gene-transfer-where-bacterial-DNA-can-be-transferred-from-one_W640.jpghttps://www.curioustem.org/stem-articles/horizontal-gene-transfer
Role of Biofertilizers in Agriculture
Global food production has increased by many folds as compared to the past, but still, the pace of agricultural productivity is not adequate for a rapidly increasing population. Presently, chemical fertilizers used for crop yield improvements are not compatible because of their environmental hazards and cost. Indiscriminate use of synthetic fertilizers has led to pollution and contamination of soil and water basins. This has resulted in the soil being deprived of essential plant nutrients and organic matter. It has led to the depletion of beneficial microorganisms and insects, indirectly reducing soil fertility and making crops more prone to diseases. The increasing cost of fertilizers would be unaffordable to small and marginal farmers, thus intensifying the depleting levels of soil fertility due to the widening gap between nutrient removal and supplies. In the present scenario, there has been a real resurgence of environmental-friendly, sustainable agricultural products. Biofertilizers are formulations that contain living microorganisms that have the ability to colonize crop roots and promote growth by improving nutrient availability and acquisition.
Classification of Biofertilizers
Several microorganisms and their interactions with crop plants are being used to create biofertilizers. They can be grouped in different ways based on their nature and function.
Rhizobium: Rhizobium is a soil habitat bacterium, which colonizes legume roots and fixes atmospheric nitrogen symbiotically. Morphology and physiology differ from free-living conditions to nodule bacteroids. They are the most efficient biofertilizers as per the quantity of nitrogen fixed. They have seven genera and are highly specific for forming nodules in legumes, referred to as cross inoculation.
Azotobacter: Among various Azotobacter species, A. chroococcum happens to be the dominant inhabitant in arable soils capable of fixing N2 (2-15 mg N2 fixed /g of carbon source) in culture media. The bacterium produces abundant slime, which helps in soil aggregation. The numbers of A. chroococcum in Indian soils rarely exceeds 105/g soil due to a lack of organic matter and the presence of antagonistic microorganisms in soil.
Azospirillum: Azospirillum lipoferum and A. brasilense are primary inhabitants of the soil, the rhizosphere, and intercellular spaces of the root cortex of graminaceous plants. They develop associative symbiotic relationships with graminaceous plants. Apart from nitrogen fixation, growth promoting substance production (IAA), disease resistance, and drought tolerance are some of the additional benefits of inoculation with Azospirillum.
Cyanobacteria: Both free-living as well as symbiotic cyanobacteria (blue green algae) have been harnessed in rice cultivation.
Azolla is a free-floating water fern that floats in water and fixes atmospheric nitrogen in association with the nitrogen-fixing blue green alga Anabaena azollae. Azolla can be used either as an alternate nitrogen source or as a supplement to commercial nitrogen fertilizers. Azolla is used as a biofertilizer for wetland rice and it is known to contribute 40–60 kg N/ha per rice crop.
Phosphate solubilizing microorganisms (PSM): Several soil bacteria and fungi, notably species of Pseudomonas, Bacillus, Penicillium, Aspergillus, etc., secrete organic acids and lower the pH in their vicinity to bring about the dissolution of bound phosphates in soil. Increased yields of wheat and potatoes were demonstrated due to inoculation of peat-based cultures of Bacillus polymyxa and Pseudomonas striata.
AM fungi: The transfer of nutrients, mainly phosphorus, and also zinc and sulphur from the soil milleu to the cells of the root cortex is mediated by intracellular obligate fungal endosymbionts of the genera Glomus, Gigaspora, Acaulospora, Sclerocysts, and Endogone, which possess vesicles for storage of nutrients and arbuscules for funneling these nutrients into the root system. By far, the commonest genus appears to be Glomus, which has several species distributed throughout the soil.
Silicate solubilizing bacteria (SSB): Microorganisms are capable of degrading silicates and aluminum silicates. Several organic acids are produced during the metabolism of microbes, and these have a dual role in silicate weathering. They supply H+ ions to the medium and promote hydrolysis. Also, they promote the removal of and retention of organic acids like citric, oxalic acid, keto acids, and hydroxy carbolic acids, in the medium in a dissolved state.
Plant growth promoting rhizobacteria (PGPR): The group of bacteria that colonize roots or rhizosphere soil and are beneficial to crops is referred to as plant growth promoting rhizobacteria (PGPR). The PGPR inoculants promote growth through suppression of plant disease (termed Bioprotectants), improved nutrient acquisition (termed Biofertilizers), or phytohormone production (termed Biostimulants). Species of Pseudomonas and Bacillus can produce as yet not well characterized phytohormones or growth regulators that cause crops to have greater numbers of fine roots, which have the effect of increasing the absorptive surface of plant roots for uptake of water and nutrients. These PGPR are referred to as Biostimulants, and the phytohormones they produce include indole-acetic acid, cytokinins, gibberellins, and inhibitors of ethylene production.
The formulation of biofertilizers is a crucial multistep process that includes the mixing of a suitable carrier with an inoculant, providing optimal conditions during storage, packaging, and dispatch, and ensuring survival and establishment after introduction into soil.
Methods of Application of Biofertilizers
Seed Treatment: 200 g of biofertilizer is suspended in 300-400 mL of water and mixed gently with 10 kg of seeds using an adhesive like gum acacia, jiggery solution, etc. The seeds are then spread on a clean sheet or cloth under shade to dry and can be used immediately for sowing.
Seedling Root Dip: This method is used for transplanted crops. For rice crops, a bed is made in the field and filled with water. Recommended fertilizers are mixed in this water and the roots of seedlings are dipped for 8–10 h and transplanted.
Soil Treatment: 4 kg each of the recommended biofertilizers is mixed in 200 kg of compost and kept overnight. This mixture is incorporated in the soil at the time of sowing or planting.
Advantages of Using Biofertilizers
Some of the advantages associated with biofertilizers include:
- They are eco-friendly as well as cost-effective.
- Their use leads to soil enrichment, and the quality of the soil improves with time.
- Though they do not show immediate results, the results shown over time are spectacular.
- These fertilizers harness atmospheric nitrogen and make it directly available to the plants.
- They increase the phosphorus content of the soil by solubilizing and releasing unavailable phosphorus.
- Biofertilizers improve root proliferation due to the release of growth-promoting hormones.
- Microorganisms convert complex nutrients into simple nutrients for the availability of the plants.
- Biofertilizer contains microorganisms which promote the adequate supply of nutrients to the host plants and ensure their proper development of growth and regulation in their physiology.
- They help in increasing the crop yield by 10–25%.
- Biofertilizers can also protect plants from soil-borne diseases to a certain degree.
Figure 1 – Mechanisms of plant growth promoting Rhizobacteria
Constraints in Biofertilizer Technology
Despite the fact that biofertilizer technology is a low-cost, environmentally friendly technology, several constraints limit its application or implementation. The constraints may be:
- Technological constraints like the unavailability of good quality carrier material and a lack of qualified technical personnel in production units.
- Infrastructural constraints like lack of essential equipment, power supply, etc.
- Financial constraints like non-availability of sufficient funds and problems in getting bank loans.
- Environmental constraints like seasonal demand for biofertilizers, simultaneous cropping operations, and a short span of sowing/planting in a particular locality, etc.
- Human resource and quality constraints, such as a lack of technically qualified personnel in production units and a lack of appropriate production technique training,
- Unawareness of the benefits of the technology due to problems in adoption of the technology by the farmers due to different methods of inoculation, no visual difference in the crop growth immediately as that of inorganic fertilizers.
Application of biological fertilizers is thought to be a key element in maintaining soil fertility and crop productivity at a sufficiently high level, which is indispensable to achieve the sustainability of farming. Biofertilizers may also help mitigate pitfalls arising from the growing demand of the global population for food and from the widespread chemicalization of agroecosystems. The changing approach to agricultural practices makes biofertilizers a vital part of modern-day crop production and emphasizes the significance of biological inoculants in forthcoming years.
References
DebmalyaDasguptaa,KulbhushanKumarbRashi,MiglanibRojita,MishracAmrita Kumari,PandadSatpal SinghBishtb.(2021). Microbial biofertilizers: Recent trends and future outlook:Toward the establishment of Microbial biofertilizers: Recent trends and future outlook.
S. Kannaiyan, Cyanobacterial biofertilizer technology for rice crops. In: Algal biotechnology (Trivedi, P.C. Ed.). Pointer publishers, Jaipur, India.2001. Rakesh Kumar, Narendra Kumawat,Yogesh Kumar Sahu.(2017). Role of Biofertilizers in Agriculture.
Image courtesy
Featured image – https://Anuvia aims to have its biofertilizer on 20m farm acres by 2025 (agfundernews.com)
Figure 1 – https://www.aimpress.com/article/id/371
What’s Next for Sri Lanka’s Agriculture Sector?
Majority of the Sri Lankan families, including yours and mine, are facing an unprecedented food crisis. With the country’s acute malnutrition among children under 5 years, reaching 17%, Sri Lanka has secured the second highest malnutrition rate across South Asia, a position of shame and disappointment.
Many factors, including the Covid-19 pandemic, national issues such as poor governance and irrational policy making can be identified as major catalysts which have escalated this nutritional crisis.
Significant effects have been raised due to the continuous rising of food costs, which was reported as a 90.9 percent increase in July 2022 (Department of Census and Statistics – Sri Lanka). While a higher level of inflation is expected in the future, why has Sri Lanka’s inflation been so high and identification of the influence of the agricultural sector is of utmost importance.
In a broader perspective, Sri Lanka’s foreign currency shortage and bad credit reputation has resulted in continuous failures of purchasing and importing key agricultural imports such as fuel, fertilizer and pesticides. This in turn has led to almost halving of the gross agricultural production (BBC.com). While blames are being shared and thrown across, an important realization noted through this crisis was the heavy reliance on imports and unsustainable nature of Sri Lanka’s agricultural sector.
Although historically known to have produced enough rice to ship excess to Myanmar, today Sri Lanka is a recipient of rice donations from the same nation. There’s much to reflect and lament on where and what went wrong and even now it is not too late to take mitigatory actions.
Donations from friendly nations: Myanmar, China and India as well as global organizations such as the UN’s World Food Program play a vital role. Nevertheless, questions on their proper management and equivalent distribution exists in a major scale.
For short-term and long-term solutions, an in-depth analysis of the current and prevalent issues must be carried out and a systematic action plan must be implemented. This should be done while integrating the expert knowledge and advice of academics and researchers across Sri Lanka – frequently disregarded by all-knowing political factions.
Agriculture is of global importance and therefore, almost every day, a novel discovery inching us closer towards global food security, is being released. However, these require considerable investments and specialized training which is a heavy price to pay for a country already in crisis.
Therefore, search for feasible solutions that can be employed in a localized and short-term framework is of paramount importance.
1. Promoting urban farming. Farming in Sri Lanka has been concentrated in certain regions away from urbanization. Although it makes sense for large scale operations, small or medium scale farming within urban regions should be encouraged including individual households.
2. Improving existing infrastructure to facilitate easy transportation, distribution of agricultural products from farmer to consumer and minimizing mediator costs.
3. Reducing food wastage. Despite the ongoing crisis, food wastage by individuals and corporations is a significant problem. Focusing on demand vs. supply, and donation of excess daily produce can help feed many.
4. Providing specialized, ground-level support and guidance to farmers with available newest technologies and local discoveries.
5. Recruiting the private sector for aid, under the corporate social responsibility frameworks.
6. Raising public awareness of the ongoing crisis and creating a collective social impact via Scientific communication.
Although feasible solutions are available, without proper guidance or monitoring, it is difficult to achieve them. A national strategy with a clear set of objectives and goals is imperative if we are to overcome this crisis because, nutritional Crisis might not be your problem today, but it could be yours tomorrow.
References
http://www.statistics.gov.lk/
https://www.bbc.com/news/business-62990385
https://srilankabrief.org/sri-lankas-agricultural-scientific-community-predicts-substantial-yield-losses-in-agricultural-production-due-to-govts-new-policy/
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Featured image – https://srilankabrief.org/sri-lankas-agricultural-scientific-community-predicts-substantial-yield-losses-in-agricultural-production-due-to-govts-new-policy/
Use of Biofertilizer in Modern Agriculture
Modernized agricultural methods play a significant role in meeting the food demands of a growing world population, which has also led to an increasing dependence on chemical fertilizers and pesticides. The term “chemical fertilizer” refers to any number of synthetic compound substances created specifically to increase crop yield and composed of known quantities of nitrogen, phosphorus, and potassium, and their exploitation causes air and groundwater pollution by eutrophication of water bodies. Because of this, recent attention has been given to developing an environmentally friendly bio fertilizer.
The new trend in agricultural production is the use of biological-based organic fertilizers as an alternative to agro-chemicals. This means that soil fertilization relies on organic inputs to improve nutrient supply and conserve field management. Organic farming is one such strategy that not only ensures food safety but also adds to the biodiversity of the soil. The additional advantages of bio fertilizers include longer shelf life, causing no adverse effects to the ecosystem. Bio fertilizer is made up of free living bacteria that promote plant growth, increase productivity through root strengthening, and help to reduce the amount of synthetic fertilizer used on crops.
Organic farming is mostly dependent on the natural microflora of the soil, which constitutes all kinds of useful bacteria and fungi, including the arbuscular mycorrhiza fungi (AMF) and plant growth-promoting rhizobacteria (PGPR). Through nitrogen fixation, phosphate and potassium solubilization or mineralization, the release of plant growth regulating substances, the production of antibiotics, and the biodegradation of organic matter in the soil, biofertilizers keep the soil environment rich in all types of micro- and macronutrients.
When bio fertilizers are applied as a coating for seeds or directly as soil inoculants, the microbes present multiply and participate in nutrient cycling, boosting crop productivity.
In general, 60% to 90% of the total applied fertilizer is lost, and the remaining 10% to 40% is taken up by plants in the traditional use of chemical fertilizer. In this regard, microbial inoculants have paramount significance in integrated nutrient management systems to sustain agricultural productivity and a healthy environment. The PGPR or co-inoculants of PGPR and AMF can increase the nutrient use efficiency of fertilizers.
The rhizosphere, which is the narrow zone of soil surrounding plant roots, can comprise up to 1011 microbial cells per gram of root and over 30,000 prokaryotic species. There are microbial strains providing numerous services to crop plants, like organic matter decomposition, nutrient acquisition, water absorption, nutrient recycling, weed control, and bio-control. Rhizosphere microbial communities are an alternative to chemical fertilizers and have become a subject of great interest in sustainable agriculture and bio-safety programs.
A major focus in the coming decades will be on safe and environmentally friendly methods of sustainable crop production by utilizing beneficial microorganisms.Such microorganisms, in general, consist of diverse naturally occurring microbes whose inoculation into the soil ecosystem advances soil physicochemical properties, soil microbe biodiversity, soil health, plant growth and development, and crop productivity. The agriculturally useful microbial populations include plant growth promoting rhizobacteria, N2-fixing cyanobacteria, mycorrhiza, plant disease suppressive beneficial bacteria, stress tolerance endophytes, and bio-degrading microbes.
These biofertilizers are a supplementary component to soil and crop management traditions. Azotobacter, Azospirillum, Rhizobium, cyanobacteria, phosphorus and potassium solubilising microorganisms, and mycorrhizae are some of the PGPRs that were found to increase in the soil under no tillage or minimum tillage treatment. Efficient strains of Azotobacter, Azospirillum, Phosphobacter, and Rhizobacter can provide a significant amount of nitrogen to plants and increase the plant height, number of leaves, stem diameter, percentage of seed filling, and seed dry weight. Similarly, in rice, the addition of Azotobacter, Azospirillum, and Rhizobium promotes the physiology and improves the root morphology.
References
Abbaszadeh-Dahaji, P., Masalehi, F., and Akhgar, A. (2020). Improved growth and nutrition of sorghum (Sorghum bicolor) plants in a low-fertility calcareous soil treated with plant growth–promoting rhizobacteria and Fe-EDTA. J. Soil Sci. Plant Nutr.
Agnolucci, M., Avio, L., Pepe, A., Turrini, A., Cristani, C., Bonini, P., et al. (2019). Bacteria associated with a commercial mycorrhizal inoculum: community composition and multifunctional activity as assessed by illumina sequencing and culture-dependent tools.
Ahmed, B., Midrarullah, and Sajjad Mirza, M. (2013). Effects of inoculation with plant growth promoting rhizobacteria (PGPRs) on different growth parameters of cold area rice variety, Fakre malakand. Afr. J. Microbiol.
Ahmed, E., and Holmström, S. J. M. (2014). Siderophores in environmental research: roles and applications. Microb. Biotechnol.
Alori, E. T., Glick, B. R., and Babalola, O. O. (2017). Microbial phosphorus solubilization and its potential for use in sustainable agriculture.
Image courtesy
Featured image – https://biomassmagazine.com/articles/19167/unlocking-biofertilizer-as-additional-revenue-source
The Secret of Poinsettia with Phytoplasma
Poinsettia is a colorful blooming potted plant, in the Euphorbia family. It is a popular holiday plant especially used for decorations during the winter holidays in Europe and American countries. Poinsettia is more attractive because of its colorful bracts (leaves). Different colored poinsettias in the market are from different varieties. The Poinsettia flower is made up of bracts that look like a petal, but in the center, there are tiny yellow flowers called cyathia. The potted poinsettia has more branches and it grows like a small bush and it is an important feature in the market. They are usually produced through cutting propagation of the axial bud or terminal bud of vegetative stock plants. It is necessary to treat the plant with chemicals 6-7 times. Today all the commercial poinsettia varieties are planted with free branching phenotypes. The secret of this free branching is a result of the infection by phytopathogens known as Phytoplasma.
Phytoplasmas are a group of prokaryotes which are very small bacteria without a cell wall but covered by a membranous envelope. Phytopathogenic studies of various genes of phytoplasma suggest that they are descended from walled-bacteria in the Bacillus/Clostridium group. They are less than 1µm in diameter with a reduced genome greatly in size. Therefore, they lack enzymes needed for biosynthetic pathways. Thus, what should they do to obtain the necessary compounds? All known phytoplasmas infect plants and transmit through insect vectors and obtain necessary compounds from plants and vectors. Phytoplasmas are phloem-limited pathogens. In plants phytoplasma mainly lives in the sieve cells of phloem tissues. Therefore, phytoplasma transmission has been confirmed only through phloem-feeding insects. Phloem-feeding insects such as leafhoppers and planthoppers of the order Hemiptera are identified as vectors. Vectors acquire phytoplasmas passively during feeding and have a long time period of acquisition during feeding time to acquire sufficient phytoplasmas to establish in the vector body. It can take up to nearly three weeks. Once phytoplasmas are established, they will be found in most organs of the infected vector. Phytoplasma replicates in the salivary glands of vector insects. In addition, phytoplasma can be transmitted through vegetative propagation.
Phytoplasma diseases spread mainly in tropical and sub-tropical countries. The presence of phytoplasma is associated with a wide range of symptoms. Phyllody is the development of leaf-like growth in place of normal flowers. Some plants develop green color in place of normal flower color (green flowers) called virescence and witches' broom is an abnormal excessive proliferation of axillary shoots resulting in a broom-like growth. The other characteristic symptom is little leaves, the development of abnormally small leaves.
The proliferation of axillary shoots is useful in the production of poinsettia. Witches' broom symptoms are shown at the infection of poinsettia. The phytoplasma associated with poinsettia branching belonging to group 16SrIII-H produces more auxiliary shoots that have more than one coloured shoot with flowers. Therefore, some symptoms of phytoplasma are commercially important except for their negative impacts.
References
Pondrella, M.; Caprara, L.; Bellardi, M.G.; Bertaccini, A., Roll of Different Phytoplasma in Inducing Poinsettia Branching. Proc.10th IS Virus Disease Ornamentals, 2002, pp 170-176.
Assunta, B., Plants and Phytoplasma: When bacteria modify Plants. MDPI 2022, 11
Hogenhout, S.A., Plant Pathogen – Minor (Phytoplasma). Elsevier 2009
Kumari, S.; Nagendran, K.; Bahadur Rai, A.; Singh, B.; Rao, G.P.; Bertaccini, A., Global Status of Phytoplasma Disease in Vegetable crop. Frontiers in Microbiology 2019, 10
Bertaccini, A.; Oshima, K.; Maejima, K.’; Namba, S., Phytoplasma: Plant Pathogenic Bacteria-III, Chapter 2
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Featured image – https://www.ambius.com/blog/wp-content/uploads/2016/12/Poinsettia-1024×679.jpg
Microbial Biopesticides
Introduction to biopesticides
Biopesticides are biological agents used to control pest populations.They include botanicals, pathogenic microbes such as fungi, bacteria, viruses, other natural enemies of pests such as parasitoids, predators, nematodes and semiochemicals.
Biopesticides can be divided into three major categories.
1. Microbial pesticides
These consist of microorganisms as the active ingredient. Microbial pesticides can control many kinds of pests. However, the active ingredient of the biopesticide is relatively specific for its target pest.
E.g., Bacillus thuringiensis: each strain of this bacterium produces a different mix of proteins that specifically kills one or few related species of insect larvae.
2. Biochemical Pesticides
These are naturally occurring substances that control pests by non–toxic mechanisms in contrast to conventional pesticides that either kill or inactivate pests.
E.g., Sex pheromones, various scented plant extracts that interfere with the mating behavior of pests.
3. Plant-incorporated protectants (PIPs)
This is where plants produce certain pesticidal constituents by themselves from genetic material that are inserted to the plant genome.
E.g., Scientists can extract the gene for the Bacillus thuringiensis (Bt.) pesticidal protein and introduce the gene into the plant genome. Thereby, the plant can manufacture the particular pesticidal protein that inhibit the pest when it feeds on the plant.
An insight to microbial biopesticides
In this category, the active ingredient is a microorganism that either occurs naturally or is genetically engineered.
The pesticide action may be from the organism itself or from a substance it produces. The most commonly used microbial biopesticides are the living organisms which are pathogenic for the pest of interest. They include,
(i) Biofungicides (E.g., Trichoderma, Pseudomonas, Bacillus)
(ii) Bioherbicides (E.g., Phytophthora)
(iii) Bioinsecticides (E.g., Bacillus thuringiensis)
The active ingredient of the microbial pesticide (which is a microorganism such as bacterium, fungus, virus, protozoa, alga, rickettsia, mycoplasma or nematode) suppresses pests either by producing toxic metabolites, competition, or various other modes of action.
An example for a microbial biopesticide; Bacterial biopesticides
Bacterial biopesticides are the most common form of microbial pesticides that function in multiple ways. Generally, they are used as insecticides, although they can be used to control the growth of plant pathogenic bacteria and fungi.
As an insecticide, they are generally specific to individual species of moths, butterflies, beetles, flies, and mosquitoes. To be effective, they must come into contact with the target pest and may require to be ingested. In insects, bacteria disrupt the digestive system by producing endotoxins that are often specific to the particular insect pest.
When used to control a pathogenic bacteria or fungus, the bacterial biopesticide colonizes the plant and crowds out the pathogenic species. The most widely used microbial pesticides are subspecies and strains of B. thuringiensis during its sporulation synthesizes crystalline infusions containing proteins known as endotoxins or Cry proteins, which have insecticidal properties.
Due to their high efficiency and safety in the environment, B. Thuringiensis and Cry proteins are considered as sustainable alternatives to chemical pesticides for the control of insects.
References
Ruiu, L. (2018). Microbial Biopesticides in Agroecosystems. Agronomy, 8(11), 235. https://doi.org/10.3390/agronomy8110235
What are Biopesticides? | US EPA. US EPA. (2022). Retrieved from https://www.epa.gov/ingredients-used-pesticide-products/what-are-biopesticides.
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