Plant Pathogens in Irrigation Water: Challenges and Opportunities

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    Plant Pathogens in Irrigation Water: Challenges andOpportunitiesC. X. Hong a & G. W. Moorman ba Department of Plant Pathology, Physiology, and Weed Science, Virginia PolytechnicInstitute and State University, Hampton Roads Agricultural Research and Extension Center ,Virginia Beach, VA, 23455-3315b Department of Plant Pathology, The Pennsylvania State University , University Park, PA,16802-4506Published online: 18 Jan 2007.

    To cite this article: C. X. Hong & G. W. Moorman (2005) Plant Pathogens in Irrigation Water: Challenges and Opportunities,Critical Reviews in Plant Sciences, 24:3, 189-208, DOI: 10.1080/07352680591005838

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  • Critical Reviews in Plant Sciences, 24:189208, 2005Copyright c Taylor & Francis Inc.ISSN: 0735-2689 print / 1549-7836 onlineDOI: 10.1080/07352680591005838

    Plant Pathogens in Irrigation Water: Challengesand Opportunities

    C. X. HongDepartment of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and StateUniversity, Hampton Roads Agricultural Research and Extension Center, Virginia Beach, VA 23455-3315

    G. W. MoormanDepartment of Plant Pathology, The Pennsylvania State University, University Park, PA 16802-4506

    Plant pathogens in irrigation water were recognized early inthe last century as a significant crop health issue. This issue has in-creased greatly in scope and degree of impact since that time and itwill continue to be a problem as agriculture increasingly dependson the use of recycled water. Plant pathogens detected from wa-ter resources include 17 species of Phytophthora, 26 of Pythium, 27genera of fungi, 8 species of bacteria, 10 viruses, and 13 species ofplant parasitic nematodes. There is substantial evidence demon-strating that contaminated irrigation water is a primary, if not thesole, source of inoculum for Phytophthora diseases of numerousnursery, fruit, and vegetable crops. These findings pose great chal-lenges and opportunities to the plant pathology community. A va-riety of water treatment methods are available but few have beenassessed for agricultural purposes under commercial conditions.Investigations into their technical feasibility and economics are ur-gently needed. Aquatic ecology of plant pathogens is an emergingfield of research that holds great promise for developing ecologi-cally based water decontamination and other strategies of pathogenmitigation. Pathogen detection and monitoring as well as biologicaland economic thresholds are much-needed IPM tools and shouldbe priorities of future research. Teaming with hydrologists, agri-cultural engineers, ecologists, geneticists, economists, statisticians,and farmers is essential to effectively attack such a complex issueof growing global importance. Research should proceed in con-junction with nutrient and pesticide management studies in a co-ordinated and comprehensive approach as they are interrelatedcomponents of water resource conservation and protection.

    Keywords aquatic ecology, biological threshold, pathogen detectionand monitoring, IPM, water resource conservation andprotection

    I. INTRODUCTIONOne factor common to all crop production is the need for

    water. As a common denominator in growing plants, water and

    Address correspondence to C. X. Hong, Department of Plant Pathol-ogy, Physiology, and Weed Science, Virginia Polytechnic Institute andState University, Hampton Roads Agricultural Research and ExtensionCenter, Virginia Beach, VA 23455-3315. E-mail:

    all that it contains is a potential risk factor, particularly if it mustbe repeatedly applied to crops to compensate for limited rainfallor made available at a specific time in the crops development.If the water carries undesirable chemicals or microbes, an entirecrop can be lost. The subject of this review, the risk posed bythe plant pathogens in irrigation water, was recognized earlyin the last century as a significant crop health issue (Bewleyand Buddin, 1921; Oyler and Bewley, 1937). Whether the initialsource of water harbors pathogens or pathogens enter the wateralong the path of distribution, one consequence is the repeatedinoculation of plants with the pathogens.

    The problem of plant pathogens in irrigation water is aggra-vated by the increasing use of recycled water. Recycling irri-gation in some locales is crucial to comply with stringent wa-ter policies and regulations. As the concern over water scarcityspreads, agricultural use of water resources is being more closelymonitored and regulated by governments. In some localities, it ismandated or considered highly desirable that runoff and leachatefrom irrigated agricultural areas be captured to prevent nitro-gen, phosphorus, and pesticides from contaminating ground-water and surface supplies (Kabashima, 1993; von Broembsenet al., 2001; Norman et al., 2003). The trend in the United Statesis for farms to be viewed as point sources of pollution. If desig-nated as such by regulatory agencies, farmers will be requiredto comply with some of the same regulations as manufacturers.Although farmers are forced to look at production methods innew ways because of this possibility, it is important to note thatmost farm families live close to and utilize for personal purposesthe same water resources used as for growing crops or raisinglivestock (Scarpa, 2000). Farmers too are very interested in pre-venting the degradation of the water and conserving this vitalresource. In the course of devising and implementing best waterconservation management practices, the issue of plant pathogensin water has come to the forefront.

    There are reports of the presence of almost every majorpathogen group in water. In this review, we will discuss the possi-ble sources of plant pathogens in irrigation water, how irrigationmay distribute these pathogens, the methods used to detect and





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    monitor the presence of plant pathogens, and the current tech-nology available for the mitigation of pathogens in water. Ourobjectives are to highlight selected papers that are the basis ofour current understanding of the problem of plant pathogens inwater and to point out what additional knowledge is needed toattack this issue of global importance.


    Well water seldom contains plant pathogens (McCarter-Zorner et al., 1984; Pottorff and Panter, 1997; Themann et al.,2002; Yun, 2003). If, however, the well is not cased or if the headis not sealed near the surface, runoff carrying sediment can enterthe well and contaminate the water with plant pathogens. Whenwater is collected in cisterns recharged by rainfall from the roof,it may not necessarily be free of pathogens, but the number ofcontaminant species would be limited (Rattink, 1991). Runoff ofsurface water or wind-blown soil can contaminate water storagetanks, regardless of how the water is initially collected. Surfacewater supplies including ponds, lakes, rivers, and streams aswell as manmade reservoirs and canals are all possible sourcesof plant pathogens that originate from the underlying and sur-rounding soil or plant debris (Tables 16). Through these variousavenues, the initial water used for irrigation may be the sourceof plant pathogens.

    If the water source is free of pathogens, then pathogens mayenter the water at several points along the distribution path. Anyirrigation method in which the water comes in contact with soilor plant debris has an increased likelihood of acquiring plantpathogens. Furrow flooding and runoff from other methods ofirrigation can then carry soilborne pathogens throughout thewatered area. In outdoor p