Berry shrivel (BS) is a ripening disorder of unknown cause and sporadic appearance that has been increasingly observed in vineyards around California. BS has often been mistaken for another disorder, bunchstem necrosis (BSN), but we have found that the disorders can be distinguished by the condition of the rachis of affected clusters. The rachises on BS clusters are green and healthy looking, while BSN rachises are brown necrotic. BS fruit had less sugar, lower pH, and reduced coloration several weeks before visible shriveling of the fruit. These compositional differences are maintained throughout the ripening period. BS fruit stops sugar accumulation about two weeks prior to symptom appearance. The apparent rise in Brix of BS fruit after this point is due to dehydration of the fruit and concentration of existing solutes. BS also appears to be a vine phenomenon, as nonshriveled clusters on a vine with shriveled clusters are also compositionally different than fruit from a healthy vine. These ?likely to shrivel? (LTS) clusters have compositions intermediate between BS clusters and clusters from a healthy vine (control clusters). Nonshriveled clusters on a vine with BS clusters also stop, or significantly slow, sugar accumulation at the same time as BS fruit does.
Since the BS phenomenon appears to be due to phloem dysfunction, girdling treatments were set up at different developmental times in Davis and at the Oakville Experimental Vineyard (OEV) in Napa County. Artificially stopping sugar accumulation by girdling caused the berries to develop with reduced coloration and the berries eventually (3-4 weeks post girdling) began to shrivel.
There has been a trend at OEV for vines with a history of BS to be less water stressed (as determined by leaf water potential measurements) than control vines. To test the hypothesis that vine water status exacerbates or mitigates the incidence or severity of BS, an irrigation trial was set up in the Alexander Valley in Sonoma County. One irrigation treatment applied water at a rate that vastly exceeded the grower?s standard irrigation (approximately 5 gph as compared to 0.5 gph) and vines in the other treatment were not irrigated. While these treatments did affect the vine water status, they did not affect the BS incidence in the vines.
The hormone CPPU (Prestige®) was sprayed at two concentrations (2 ppm and 4 ppm) after set (at 8mm berry size) at two sites (OEV and Alexander Valley) in order to assess its effect on the incidence of BS and BSN. Neither of the hormone treatments, at either concentration, had an effect on the incidence of BS or BSN.
The BS disorder can be propogated by chip buds. Budding was done in 2003. Vines propagated with buds collected from vines with a history of BS had reduced sugar accumulation, shorter shoots after budbreak, and reduced weight per berry compared to vines propagated from healthy material. Wines were made with the addition of different amounts of BS and BSN fruit from the 2006 harvest (0%, 5% and 10% by weight). All of the wines fermented to dryness and will be used for difference testing and potentially descriptive analysis if differences can be detected.
Much of the data contained in this report has been submitted for publication to AJEV.