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Plant Pathogens in Irrigation Water: Challenges and Opportunities C This article was downloaded by: [EBSCOHost EJS Content Distribution - Current] On: 29 January 2011 Access details: Access Details: [subscription number 925797205] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37- 41 Mortimer Street, London W1T 3JH, UK Critical Reviews in Plant Sciences Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713400911 Plant Pathogens in Irrigation Water: Challenges and Opportunities C. X. Honga; G. W. Moormanb a Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Hampton Roads Agricultural Research and Extension Center, Virginia Beach, VA b Department of Plant Pathology, The Pennsylvania State University, University Park, PA To cite this Article Hong, C. X. and Moorman, G. W.(2005) 'Plant Pathogens in Irrigation Water: Challenges and Opportunities', Critical Reviews in Plant Sciences, 24: 3, 189 — 208 To link to this Article: DOI: 10.1080/07352680591005838 URL: http://dx.doi.org/10.1080/07352680591005838 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Critical Reviews in Plant Sciences, 24:189–208, 2005 Copyright c Taylor & Francis Inc. ISSN: 0735-2689 print / 1549-7836 online DOI: 10.1080/07352680591005838 Plant Pathogens in Irrigation Water: Challenges and Opportunities C. X. Hong Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Hampton Roads Agricultural Research and Extension Center, Virginia Beach, VA 23455-3315 G. W. Moorman Department of Plant Pathology, The Pennsylvania State University, University Park, PA 16802-4506 all that it contains is a potential risk factor, particularly if it must Plant pathogens in irrigation water were recognized early in be repeatedly applied to crops to compensate for limited rainfall the last century as a significant crop health issue. This issue has in- or made available at a specific time in the crop’s development. creased greatly in scope and degree of impact since that time and it If the water carries undesirable chemicals or microbes, an entire will continue to be a problem as agriculture increasingly depends crop can be lost. The subject of this review, the risk posed by on the use of recycled water. Plant pathogens detected from wa- ter resources include 17 species of Phytophthora,26ofPythium,27 the plant pathogens in irrigation water, was recognized early genera of fungi, 8 species of bacteria, 10 viruses, and 13 species of in the last century as a significant crop health issue (Bewley plant parasitic nematodes. There is substantial evidence demon- and Buddin, 1921; Oyler and Bewley, 1937). Whether the initial strating that contaminated irrigation water is a primary, if not the source of water harbors pathogens or pathogens enter the water sole, source of inoculum for Phytophthora diseases of numerous along the path of distribution, one consequence is the repeated nursery, fruit, and vegetable crops. These findings pose great chal- lenges and opportunities to the plant pathology community. A va- inoculation of plants with the pathogens. riety of water treatment methods are available but few have been The problem of plant pathogens in irrigation water is aggra- assessed for agricultural purposes under commercial conditions. vated by the increasing use of recycled water. Recycling irri- Investigations into their technical feasibility and economics are ur- gation in some locales is crucial to comply with stringent wa- gently needed. Aquatic ecology of plant pathogens is an emerging ter policies and regulations. As the concern over water scarcity field of research that holds great promise for developing ecologi- cally based water decontamination and other strategies of pathogen spreads, agricultural use of water resources is being more closely mitigation. Pathogen detection and monitoring as well as biological monitored and regulated by governments. In some localities, it is and economic thresholds are much-needed IPM tools and should mandated or considered highly desirable that runoff and leachate be priorities of future research. Teaming with hydrologists, agri- from irrigated agricultural areas be captured to prevent nitro- cultural engineers, ecologists, geneticists, economists, statisticians, gen, phosphorus, and pesticides from contaminating ground- and farmers is essential to effectively attack such a complex issue of growing global importance. Research should proceed in con- water and surface supplies (Kabashima, 1993; von Broembsen junction with nutrient and pesticide management studies in a co- et al., 2001; Norman et al., 2003). The trend in the United States ordinated and comprehensive approach as they are interrelated is for farms to be viewed as point sources of pollution. If desig- components of water resource conservation and protection. nated as such by regulatory agencies, farmers will be required to comply with some of the same regulations as manufacturers. Downloaded By: [EBSCOHost EJS Content Distribution - Current] At: 22:49 29 January 2011 Keywords aquatic ecology, biological threshold, pathogen detection Although farmers are forced to look at production methods in and monitoring, IPM, water resource conservation and new ways because of this possibility, it is important to note that protection most farm families live close to and utilize for personal purposes the same water resources used as for growing crops or raising livestock (Scarpa, 2000). Farmers too are very interested in pre- I. INTRODUCTION venting the degradation of the water and conserving this vital One factor common to all crop production is the need for resource. In the course of devising and implementing best water water. As a common denominator in growing plants, water and conservation management practices, the issue of plant pathogens in water has come to the forefront. There are reports of the presence of almost every major Address correspondence to C. X. Hong, Department of Plant Pathol- ogy, Physiology, and Weed Science, Virginia Polytechnic Institute and pathogen group in water. In this review, we will discuss the possi- State University, Hampton Roads Agricultural Research and Extension ble sources of plant pathogens in irrigation water, how irrigation Center, Virginia Beach, VA 23455-3315. E-mail: [email protected] may distribute these pathogens, the methods used to detect and 189 190 C. X. HONG AND G. W. MOORMAN monitor the presence of plant pathogens, and the current tech- impervious “ebb and flow” or “flood and drain” benches that are nology available for the mitigation of pathogens in water. Our temporarily flooded with water and then drained to tanks where objectives are to highlight selected papers that are the basis of the water is stored until pumped back onto the benches at the next our current understanding of the problem of plant pathogens in irrigation cycle. A variation of this technique, termed “flooded water and to point out what additional knowledge is needed to floor” irrigation, positions containers of plants on an impervi- attack this issue of global importance. ous floor with a surrounding low curbing that allows the entire production floor to be flooded to the depth of a few centime- II. WATER SOURCES, IRRIGATION METHODS, AND ters during irrigation and then drained away to a storage tank for PLANT PATHOGENS reuse. Equipment driven across these floors and workers travers- Well water seldom contains plant pathogens (McCarter- ing the area can be the means of introducing contaminated soil Zorner et al., 1984; Pottorff and Panter, 1997; Themann et al., to the water used to flood this area and ultimately to the holding 2002; Yun, 2003). If, however, the well is not cased or if the head tank and all the connecting plumbing. In hydroponic, nutrient is not sealed near the surface, runoff carrying sediment can enter film, and other methods of producing plants with bare roots, the the well and contaminate the water with plant pathogens. When main sources of pathogens are the initial water source, plants water is collected in cisterns recharged by rainfall from the roof, infected as seedlings and then placed in the system, pathogen- it may not necessarily be free of pathogens, but the number of contaminated soil allowed to get into the system, and the activity contaminant species would be limited (Rattink, 1991). Runoff of of insect vectors. surface water or wind-blown soil can contaminate water storage To summarize, the initial contamination with plant pathogens tanks, regardless of how the water is initially collected. Surface of the water supply used for irrigation
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