Weksler, H., Department of Postharvest Science, ARO, The Volcani Center, POB 6, Bet Dagan, Israel, The Hebrew University of Jerusalem, POB 12, Rehovot, Israel
Kaplunov, T., Department of Postharvest Science, ARO, The Volcani Center, POB 6, Bet Dagan, Israel
Zutahy, Y., Department of Postharvest Science, ARO, The Volcani Center, POB 6, Bet Dagan, Israel
Daus, A., Department of Postharvest Science, ARO, The Volcani Center, POB 6, Bet Dagan, Israel
Beno-Mualem, D., Department of Postharvest Science, ARO, The Volcani Center, POB 6, Bet Dagan, Israel
Zemach, H., Department of Postharvest Science, ARO, The Volcani Center, POB 6, Bet Dagan, Israel
Lichter, A., Department of Postharvest Science, ARO, The Volcani Center, POB 6, Bet Dagan, Israel

Sporadic occurrences of symptoms termed 'streak browning' (SB) in 'Thompson Seedless' grapes have been observed for years in the Lachish region of Israel. It was not until 2010 and 2011 that this issue became a threat to 'Thompson' growers, with damage soaring to 50% in some vineyards. The damage was mainly superficial and characterized by elongated parallel brown streaks, which reduced the value of the fruit to below commercial value. The first symptoms usually were seen after véraison, and they intensified during fruit ripening. Microscope observations revealed superficial microcracking at the center of each streak, suggesting that these cracks were responsible for the SB. A survey of over 100 'Thompson' vineyards in the affected region showed correlation between the level of SB and poor air movement and/or light penetration. Spatial distribution of clusters with SB within the vineyard was non-random. Several lines of evidence suggested that high berry firmness was an important precondition for formation of SB, and such berries also were found to have higher soluble solids than undamaged ones. Among detached berries those with SB suffered higher rates of weight loss. Another important observation was that there was more damage in the back and bottom parts of the cluster. This pattern led to the hypothesis that SB was aggravated by foliar sprays which are slower to dry in the back part of the clusters. Dipping detached berries in solutions of organophosphate insecticides showed that they enhanced the cracking, suggesting that they have the potential to damage to the skin during repeated exposures. Spraying clusters with two organophosphate insecticides enhanced SB formation, but so also did the water control, albeit to a lower extent. The results suggest that SB can be formed on firm berries and that commercial formulations of organophosphate insecticides applied after véraison might induce microcracking and subsequent SB symptoms. © 2015 Elsevier B.V.