|Obenland, David - Dave|
|FELIZIANI, ERICA - Polytechnic University Of Marche|
|ZHU, SIJIE - California State University|
|ZHAO, XIAOFAN - California State University|
|MLIKOTA-GABLER, FRANKA - California Table Grape Commission|
|VAN ZYL, SONET - California State University|
|ROMANAZZI, GIANFRANCO - Polytechnic University Of Marche|
|BENO-MOUALEM, D - Volcani Center (ARO)|
|KAPLUNOV, T - Volcani Center (ARO)|
|LICHTER, A - Volcani Center (ARO)|
Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2015
Publication Date: 3/23/2015
Citation: Obenland, D.M., Feliziani, E., Zhu, S., Zhao, X., Margosan, D.A., Mlikota-Gabler, F., Van Zyl, S., Romanazzi, G., Smilanick, J.L., Beno-Moualem, D., Kaplunov, T., Lichter, A. 2015. Potassium application to table grape clusters after veraison increases soluble solids by enhancing berry water loss. Scientia Horticulturae. 187:58-64.
Interpretive Summary: Canopy application of potassium had been reported to increase soluble solids (sugars) in grapes, although the influence of different sources of potassium, varietal differences in response, and localization of the applied potassium in the grape berry had not been adequately characterized. A variety of different potassium salt solutions were applied to the clusters of five grape cultivars after the onset of ripening and then three weeks later in multiple trials. Potassium bicarbonate, potassium sorbate, and glycine-complexed potassium increased soluble solids content consistently by approximately 2%, while other potassium salts did not. Glycine-complexed potassium applied to ‘Sweet Scarlet’, ‘Scarlet Royal’, ‘Summer Royal’, and ‘Autumn Royal’ grapes in seven trials caused significant increases in total soluble solids, and similar results in all but one trial with ‘Sweet Scarlet’. Grapes treated with potassium tended to be smaller, but other effects on berry color and firmness were not consistent. Potassium content was increased in the grapes several cell layers below the skin. This research demonstrated that application of potassium to the grape clusters could be a useful vineyard management tool to increase sugars in grape berries and allow the fruit to be harvested sooner or enable growers to have a larger crop on the vines.
Technical Abstract: Potassium salt solutions were applied twice to clusters of several table grapes cultivars, after the onset of veraison and three weeks later. Potassium bicarbonate, potassium sorbate, and glycine-complexed potassium, a commercial fertilizer product, increased soluble solids content consistently, while other potassium salts did not. At harvest, the average of total soluble solids contents of untreated berries were 18.7%, while those treated with potassium bicarbonate, potassium sorbate, and glycine-complexed potassium were 20.5, 20.7, and 20.8%, respectively, and significantly higher. Glycine-complexed potassium applied to ‘Sweet Scarlet’, ‘Scarlet Royal’, ‘Summer Royal’, and ‘Autumn Royal’ grapes in seven trials caused significant increases in total soluble solids in all but one trial with ‘Sweet Scarlet’. The soluble solids content of 16.5% was reached 10 days earlier among the potassium treated grapes. In most trials, potassium caused significant reductions in berry weight and increased berry potassium content, while its influence on berry color and firmness were less consistent. The composition of the sugars in the berries determined as the ratio of glucose to fructose was similar between the untreated and potassium treated grapes. Potassium in the tissue of these berries was localized and semi-quantified by X-ray energy dispersive spectroscopy. Potassium bicarbonate and potassium sorbate applied to ‘Princess Seedless’ grapes after the onset of veraison increased the tissue potassium content several cell layers below the cuticle. The application of potassium salts could be used as a vineyard management tool to increase total soluble solids to facilitate earlier harvest, or to mature a larger crop on the vines. The reduction in berry size may be a benefit to remediate cluster compaction, an occasional problem with some cultivars.