Tuesday, 13 December 2016

Application of Nanotechnology in plant disease management

1. Rust in Beans 
          Hoch’s first indications that fungal organisms navigate by a sophisticated sense of touch came as a result of his team’s earlier work with the rust fungus Uromyces appendiculatus. Plant pathologists and submicron engineers determined that the fungus distinguishes minute differences in leaf surface topography in order to decide where and when to infect its host—bean plants. The team simulated leaf topography by micro fabricating ridges on silicon wafers using electron-beam lithography. They then used scanning electron microscopy and light microscopy to follow the growing rust fungus as it explored the artificial surfaces to demonstrate that the fungus orients itself to ridges similar to those on a real leaf surface. The fungus “crawls” across the ridges until it senses a correct topographical feature mimicking “stomatal lips” associated with leaf stomata, or tiny holes, on the surface of the bean leaf. This event signals the fungus to develop the primary infection structure, called an apressorium, precisely over the stomatal opening to invade the leaf tissue. Hoch and his team determined that ridges 0.5 μm high were the optimum cue that signaled for appressorium development, and that this size parameter matched almost exactly the size of the stomatal lips of the bean leaf. “The use of precision-made, highly reproducible surfaces allowed us to elucidate the mechanisms involved in the fungus’s perception of signaling cues normally located on the plant’s surface,” Hoch says. The information has provided greater insight into the inner workings of the bean rust fungus and someday may be used by bean breeders to develop bean plants with a smaller stomatal lip structure that helps make the plant more rust resistant.
2. Anthracnose in Corn
          In a related project, Hoch and his associates investigated destructive events of fungi that cause anthracnose disease on grasses. The goal was to simulate the movement of Colletotrichum graminicola, the fungus that causes anthracnose on corn and determine what features trigger the fungus to develop an appressorium. In this case rather than being formed over a stomata, the appressoria develop anywhere on the leaf surface where they exert great internal pressure needed to facilitate penetration of the leaf cuticle. Again, they used nano techniques: lithography to nanofabricate a pillared surface on silicon wafers. This lawn of miniature pillars 1.4 20 μm wide and spaced various distances apart was used to examine movement of the fungus across the surface that mimicked some of the characteristics of the host plant. Images of the fungus crawling across the nanofabricated surface have helped the researchers determine that the fungus needs to make minimum contact of at least 4.5 μm before it starts to develop appressoria. Knowing this, it is hoped that plants can be bred to possess surfaces that are less inductive to the fungus's sensing mechanisms.
3. Pierce’s Disease in Grapes
          In his current work, Hoch and his colleagues in Geneva and at the Wadsworth Center in Albany have moved from studying pathogenic fungi to studying pathogenic bacteria. Their goal is to examine how Xyllela fastidiosa moves “upstream” against the flow of sap in the plant’s vascular plumbing system, the xylem vessels. Their upstream movement has been particularly puzzling to plant pathologists because the bacteria do not have flagella, whiplash-like propelling hairs, and common to many other bacterial species. The bacteria colonize the plant’s plumbing system to the point that they block the flow of water and cause the plant to wither and die—developing what is known as Pierce’s disease. The bacteria cause millions of dollars worth of damage to grape and citrus worldwide. It is of great concern to growers in the warmer states like California, Texas, and Florida, and is of concern to grape growers in the Eastern United States. Because the bacteria cannot be readily viewed and studied by microscopy in living plants, Hoch and his post-doctoral associate, Yizhi Meng ’98, MS ’01, PhD ’03, fabricated microfluidic chambers to mimic plant xylem vessels and “infected” them with both wildtype and mutant Xylella strains created in the lab of fellow plant pathologists Thomas Burr and Yaxin Li. They created these artificial xylem vessels using a silicone elastomer that was replicated from silicon wafers onto which “master” patterns were constructed with photo-lithography. Scanning electron microscopy was used to examine the bacteria in both artificial and bona fide grape xylem. Using time-lapse light microscopy, they created “movies” of the bacteria as they colonized and “clogged” the artificial xylem. With this technology, they discovered that individual bacteria “twitched” their way upstream, against the flow, using pili, or tiny hair-like filaments, to attach the cells to the surface of the xylem wall. As the pili are repeatedly retracted and extended, the cells twitch forward—a nanometer at a time. Using these movies, they clocked bacteria moving at the microworld fast rate of 12 μm per minute against a flow velocity of about 20,000 μm per minute. On a human scale, this feat is comparable to a person swimming against the current of the Niagara River, a remarkable finding. Burr and Li, and Cheryl Galvani who also works at the Geneva experiment station, are working on transforming Xyllela so that the bacteria can no longer “twitch.”
UK University discovers perfect antimicrobial technology
          Cheap, safe and effective antimicrobial nanoparticles for food packaging have been discovered just six months into a three-year-long study at the UKbased University of Leeds' Nanomanufacturing Institute. Official results are not expected for at least another three months, but Professors Yulan Ding and Malcolm Povey and PhD candidate Lingling Zhang say already nanoparticles of zinc oxide and magnesium oxide have shown to be effective in killing microorganisms. Ding says the team is trying to find cheap, safe alternatives to nano-sized silver, which has excellent antimicrobial properties, but is expensive and as a heavy metal, is not suitable for human contact. 'We have already found some that work, such as nanoparticle zinc oxide and magnesium oxide. Results so far have been very positive,' Ding acknowledges.
          Ding’s research team is continuing to explore a larger list of cheap and inert nanoparticles for their potential effectiveness in killing microorganisms. Ding says they plan to incorporate effective antimicrobial nanoparticles into packaging materials as research progresses. 'The smart nanocomposites are assemblies of functionalized nanoparticles which are hundreds of micrometres in size and strong enough for safe and easy handling,' Ding says. The nanocomposites can be triggered to disintegrate in liquid into nanoparticles that are capable of attaching to and killing or controlling microorganisms.
Conclusion:
      In India, nanotechnology, which has already made some imprints in many areas of plant pathology, is the second craze after biotechnology for innovative research Nanotechnology now a day’s playing very important role in daily life and in agriculture. By using nanotechnological tool we can easily identify pathogen and easily management of pathogen which leads to reduction in chemical use and plant damage and environment friendly option for plant disease management, but high toxicity of nanoparticles inadvertently released in the environment may pose greater threat to man and other organisms. Therefore, nanotechnological progress is to be viewed with caution and dealt accordingly

Referencess :
Report of the OECD Workshop on the Safety of Manufactured Nanomaterials: Building Co-operation, Co-ordination and Communication (Organization for Economic Co-operation and Development, Paris, 2006).
Maynard, A. D. Nanotechnology: A Research Strategy for Addressing Risk (Woodrow Wilson International Center for Scholars, Washington DC, 2006).
Two-Year Review of Progress on Government Actions: Joint Academies' Response to the Council for Science and Technology's Call for Evidence (The Royal Society and The Royal Academy of Engineering, London, 2006). 

Article compiled by Mr. Amol Vijay Shitole (Ph.D. Scholar)
Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola (M.S.)

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