Anatomy of Russeting Induced in Concord Grape Berries by the Fungicide Chlorothalonil

¹ Department of Horticultural Sciences, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456, USA.
² Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva, NY 14456, USA.

The fungicide chlorothalonil produced russeting on the skin of Vitis labruscana Bailey cv. Concord berries growing in full sun, when applied at 3.37 kg/ha in a season-long spray program. Prebloom and full bloom application of chlorothalonil did not result in russeting. Application of single sprays showed russeting resulted from the 10-day post-bloom (p.b.) application. Visible spray residues remained on the fruit for the whole growing season. The first anatomical evidence of russeting occurred at three weeks p.b., when epidermal cells died beneath regions covered by residue and exposed to the sun. The hypodermis then developed thickened cell walls and appeared to contain mucilaginous or gummy materials. As the season progressed, fruit growth stretched the dead epidermal cells, while epidermal breaks and disruptions occurred. The innermost living cells of the hypodermis or outermost flesh cells became meristematic. This resulted in the production of either an organized periderm beneath non-broken skin regions or a less layered "filling tissue" of cell progenies, or "packets," beneath broken regions of the skin. Substantive increase in russeting did not occur after mid-August (8 weeks p.b.), and the injury, even to mature fruit sprayed six times during the season, was confined to the fruit skin. Russeted berries virtually stopped enlarging after five weeks p.b. Chlorothalonil-sprayed fruits that remained in the shade, and unsprayed fruit in sun or shade, did not russet.

Key words: Chlorothalonil, russet, grape, berry, anatomy

Submitted on October 9, 1990