Abstract
The purpose of this paper is to clarify quantitatively the effects of pH and available chlorine concentration (ACC) of electrolyzed anode-side acid water on powdery mildew (Erysiphe cichoracearum de Candolle) infection (PMI) and occurrence of a leaf burn-like physiological disorder (LBLPD) in tomato (Lycopersicon escukntum Mill. cv. Momotaro) . For this purpose, the following three types of pH-ACC-regulated water were sprayed once every 3rd or 4th day, 5 times in total at 3 to 4 d intervals, to expanded leaves of tomato plants grown in a glasshouse, and then the severity of PMI and the percentage of leaves with LBLPD were investigated : pH regulated water (pH 2.1, 2.3, 2.5, 2.7 or 7.0; ACC 0 mg L-1), ACC-regulated acid water (pH 2.5; ACC 0, 20, 30, 40 or 50 mg L-1), and ACC-regulated neutral water (pH 7.0; ACC 0, 20, 30, 40 or 50 mg L-1) . The pH and ACC of the regulated waters were adjusted with HCl or NaOH and NaClO solutions, respectively. The severity of PMI was evaluated as the increment in severity (severity increment, ΔS) from immediately before the first spray treatment. The PMI investigation showed that compared to the control (no spray) and distilled water spray treatment, each of the following three conditions significantly contributed to controlling PMI on tomato leaves : 1) pH of 2.7 or lower (more effective at lower pH) ; 2) the combination of pH of 2.5 and ACC of 20 mg L-1 or higher (more effective at higher ACC) ; and 3) ACC of 50 mg L-1. The LBLPD investigation showed that compared to the control and distilled water spray treatment, each of the following two conditions significantly contributed to causing LBLPD on tomato leaves : 1) pH of 2.7 or lower (more sever at lower pH) ; and 2) ACC of 20 mg L-1 or higher.
