The chemical pinching agent ethyl 5-(4-chlorophenyl)-2H-tetrazole acetate (PP 528) was tested for its effects on net photosynthesis (Pn) rates of leaves of 1-year-old container-grown apple (Malus domestica Borkh. cvs. Sturdeespur Delicious, Starking Delicious, Starkspur Ultrared Delicious, Starkspur Golden Delicious and Golden Delicious). Treatment with PP528 did not affect the Pn rate of leaves of either strain of ‘Golden Delicious’. Pn rates of all 3 strains of ‘Delicious’ leaves were depressed for a week after treatment with PP 528 at 30, 40, and 60 ppm, whereas 20 or 10 ppm had no significant effect. The shoot apices on both strains of ‘Golden Delicious’ trees were pinched at 60 ppm, whereas apices of the 3 strains of ‘Delicious’ were pinched at both 30 and 60 ppm.
Received for publication, November 18, 1977.
The authors thank ICI United States, Inc., Goldsboro, N. C. for supplying formulation JF 5775 and financial support.
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