Co-Authors:
Reuveni, R., Department of Plant Pathology, Agric. Res. Org., Newe Ya'ar Res. C., Ramat Yishay, Israel
Dor, G., Department of Plant Pathology, Agric. Res. Org., Newe Ya'ar Res. C., Ramat Yishay, Israel
Raviv, M., Div. of Organ. Agric. and Hort., ARO, Newe Ya'ar Res. Ctr., P.O. B., Ramat Yishay, Israel
Reuveni, M., Golan Research Institute, Univ. of Haifa, P.O. Box 97, 12900, Qasrine, Israel
Tuzun, S., Department of Plant Pathology, Auburn University, 36849, Auburn, AL, United States
Abstract:
P-containing nutrient solutions at concentrations of 5, 20 and 40 ppm, applied through a hydroponics system, provided induced systemic resistance (ISR) against Sphaerotheca fuliginea in young cucumber plants. Protection was expressed as a significant reduction (up to 92% compared with control) in the mildewed leaf area, ISR was also expressed as a 53-91% reduction in the number of S. fuliginea conidia per infected leaf area as determined on leaves 1 (first true leaf) and 2, at 9 days after inoculation, and on leaves 1-3 at 12 days after inoculation. A concentration of 20 ppm P in the hydroponics solution was found to be optimal for ISR. The optimal P concentration enhanced the uptake and increased the content of Ca in the leaves by 50% compared with the controls. Once the fungus had been established, root-applied P did not affect well-developed colonies, but, foliar application of 1% solution of mono-potassium phosphate (MKP) effectively protected the foliage against powdery mildew, regardless of the P concentration in the nutrient solutions. This treatment was persistent up to 21 days after inoculation, it significantly inhibited powdery mildew development and caused a reduction of 72.3% in sporulation of the fungus as compared with the control. The results suggest different mechanisms for the two phenomena and highlight the role of P in ISR. (C) 2000 Elsevier Science Ltd.
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