Abstract
Effects were investigated and compared of spraying the following three kind of water on the severity of powdery mildew (Sphaerotheca fuliginea Pollacci) infection and on the percentage of leaves with a leaf burn-like physiological disorder in cucumber (Cucumis sativus L. cv. Sharp7) grown in a glasshouse: well water (WW), electrolyzed anode-side water (AW) obtained by electrolysis of dilute aqueous KCl solution (ca. 0.1 g L-1), and pH-available chlorine concentration (ACC) -regulated water (RW) prepared with HCl and NaClO solutions so as to give the similar values of pH and ACC as the AW. Values of pH, ACC and oxidation-reduction potential (ORP) of the AW and RW were about 2.7, 33 ppm and 1150 mV, respectively. One hundred milliliters of each water was sprayed to all expanded leaves on 28 Oct., 31 Oct. and 4 Nov., once a day. The disease severity decreased markedly after the first spray of the AW and RW followed by a gradual decrease by the subsequent two-times sprays, while it steadily increased in the non-treated control (no spray) and WW treatment. The disease severity on 7 Nov. was significantly (p<0.01) low in the AW and RW treatments as compared to the control and WW treatment. On the other hand, spraying the AW and RW caused a leaf burn-like physiological disorder on some leaves and around 70% of leaves showed the disorder on 7 Nov., while no physiological disorder was observed in the control and WW treatment. The results indicate that the AW can be an alternative to chemical fungicides for powdery mildew in cucumber. However, it is necessary to find out a countermeasure against the physiological disorder caused by spraying AW. The results also indicate that it would be valid for use of a RW as a quasi-AW in experiments to clarify the quantitative effects of pH, ACC and ORP of an AW on crop disease control and occurrence of a leaf burn-like physiological disorder.
