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IntroductionSeveral orchid species are important commodities in South American and Asian countries. In Asia, Thailand exports high quality cut orchid flowers to EU, USA, China and Japan (Department of Agriculture, 2010). Orchid cultivation is beset by several diseases that can affect the entire crop. However, early symptom of plant disease can be treated or eradicated upon first appearance, but late symptoms, especially those that appear after harvest and are found once the plant has been exported, are unacceptable. Synthetic chemical fungicides are the most common tool used to prevent such problems, but because of their effect on humans and the environment, alternate methods are often utilized. Microbial fungicides have been introduced for controlling certain plant diseases through colonization and/or hyperparasitism modes of action (Copping and Menn, 2000). However, a newer method of eliciting natural defense mechanisms in the host plant, which is referred to as systemic acquired resistance (SAR), has recently been introduced (Wei et al., 1992; Bednarz et al., 2002). Harpin protein, derived from harp-n-gene fragment, is a SAR molecule that is produced naturally by Erwinia amylovora, a bacterium that causes the fire blight disease in apple and pear trees (Wei and Beer, 1996). It does not act directly on the disease organism or alter the DNA of the treated plants. It is currently marketed as a commercially available, broad- spectrum proteinaceous elicitor of SAR (Wei and Betz, 2007).In this study, harpin protein and a mixture of Bacillus subtilis AP-01 and Trichoderma harzianum AP-001 (Maketon et al., 2008a) were tested using chemical fungicides for comparison in controlling three orchid diseases: Curvularia lunata (Wakker) Boedijin, which causes flowers rust spot, Fusarium moniliforme (Sheldon) Wineland, which causes column blight, and Phytophthora palmivora Butler, which causes black rot in two orchid types.
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