Water-use permits, competition for water resources, and economics have stimulated the adoption of recycling irrigation water in the greenhouse and nursery industries (Ehret et al., 2001; Hong et al., 2003; Newman, 2004; Skimina, 1992). However, the use of nondisinfected, recycled irrigation water increases the risk of spreading plant pathogens, which can result in serious disease epidemics and crop losses (Hong et al., 2003). Currently, there are effective fungicides that help manage a variety of plant pathogens such as Phytophthora spp., Pythium spp., Fusarium spp., and Rhizoctonia solani (Fueda and Hirasawa, 1994; Newman, 2004), but repeated application of fungicides is increasing the development of resistance (Hong et al., 2003; Kuhajek et al., 2003) and causing environmental concerns (Schoene et al., 2006).
Other current disinfection methods of irrigation water include filtration, ultraviolet irradiation, ozonation, the use of nonionic surfactants and ionized copper, and chlorination (Ehret et al., 2001; Havard, 2003; Hong et al., 2003; Igura et al., 2004; Newman, 2004; White, 1992). Chlorination is one of the most economical water decontamination methods. It was developed to treat municipal water and still remains as one of the primary methods to disinfect water (Frink and Bugbee, 1987; Tietjen et al., 2003; White, 1992). As a result of the concern of spreading diseases throughout crops through recycled irrigation water, chlorination technology has been adopted by some nursery and greenhouse growers to disinfect their irrigation water and systems.
Literature on chlorine disinfection of fungi is limited; however, research on bacteria suggest that chlorine disinfects by disrupting various microbial subcellular components and metabolic processes, including in vitro formation of chlorinated derivatives of purine and pyrimidine nucleotide bases; oxidative decarboxylation of amino acids and other naturally occurring carboxylic acids; inhibition of enzymes involved in intermediary metabolisms; inhibition of protein biosynthesis; introduction of single- and double-stranded lesions into bacterial mutations' inhibition of membrane-mediated active transport processes and respiratory activity, uncoupling of oxidative phosphorylation accompanied by leakage of macromolecules from the cell; and physiological injury of coliform microorganisms such as Escherichia coli (Ridgway and Olson, 1982).
Chlorine demand must be considered in chlorination protocols when determining the amount of chlorine that is applied to disinfect water. Chlorine demand is the quantity of chlorine that will be consumed by organic matter and other oxidizable substances in water before a residual chlorine concentration can be obtained (Hong et al., 2003). Chlorine residual may include free residual chlorine, combined residual chlorine, or total residual chlorine. Free residual chlorine is defined as chlorine compounds in the form of dissolved chlorine gas (Cl2), hypochlorous acid (HOCl), or hypochlorite ion. Combined residual chlorine is defined as chlorine compounds that have reacted with ammonia or organic nitrogen in water to form chloramines or other chloro-derivatives. Compounds of combined chlorine include monochloramine, dichloramine (White, 1992), and nitrogen trichloride, which are less biocidal than free chlorine but still provide a disinfecting action (Hong et al., 2003). Total residual chlorine is defined as the sum of free and combined residual chlorine in water. Henceforth, free residual chlorine is referred to as free chlorine.
Use of chlorine in excess can cause visual injury, including chlorosis (bleaching action of tissues), necrotic mottling (red and black dark spots on the leaf surface), foliar necrosis (death of cells and cell tissue) (Schreuder and Brewer, 2001a; Vijayan and Bedi, 1989), premature abscission of foliage (Frink and Bugbee, 1987), decrease in plant growth (Brown, 1991; Carrillo et al., 1996; Karaivazoglou et al., 2005; Schreuder and Brewer, 2001b), leaf discoloration, curling of leaves (Brown, 1991; Karaivazoglou et al., 2005), cuticular damage resulting in increased rates of cuticular transpiration and decreased photosynthesis (Schreuder and Brewer, 2001b), damage to chloroplast membranes in conifers and reduced photosynthetic leaf area (Schreuder and Brewer, 2001a; Vijayan and Bedi, 1989), and marginal burning of leaves (Vijayan and Bedi, 1989).
There is limited research regarding the phytotoxic effects of chlorinated water on herbaceous ornamental and vegetable plants and even less so on woody ornamentals. Frink and Bugbee (1987) reported that geranium and begonia receiving chlorinated water declined in growth. Brown (1991) also reported reduction in height and flower and bud production of marigold and impatiens irrigated with chlorinated water. No research was found that has investigated the effects of chlorinated irrigation water on nursery crops irrigated daily like in typical commercial nursery operations.
The objective of this study was to investigate the phytotoxic responses and critical free chlorine threshold of five container-grown nursery liners to chlorinated irrigation water applied daily.
Brown, D. 1991 Effect of irrigating flowering plants and turf grass with chlorinated water Ontario Hydro Research Division Report K 91 73 Ontario, Canada
Carrillo, A., Puente, M.E. & Bashan, Y. 1996 Application of diluted chlorine dioxide to radish and lettuce nurseries insignificantly reduced plant development Ecotoxicol. Environ. Saf. 35 57 66
Ehret, D.L., Alsanius, B., Wohanka, W., Menzies, J.G. & Utkhede, R. 2001 Disinfestation of recirculating nutrient solutions in greenhouse horticulture Agronomie 21 323 339
Havard, P. 2003 Farm irrigation water safety initiative final report Apr. 2003 Horticulture Nova Scotia, Nova Scotia Agricultural College Nova Scotia, Canada
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Schreuder, M.D.J. & Brewer, C.A. 2001b Persistent effects of short-term, high exposure to chlorine gas on physiology and growth of Pinus ponderosa and Pseudotsuga menziesii Ann. Bot. (Lond.) 88 197 206
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