Inception, Diagnosis, and Consequences of the Berry Shrivel Disorder

This project seeks the cause of the berry ripening disorder, berry shrivel, that has been
increasingly observed in vineyards in Napa and Sonoma Counties. The disorder results in
costly crop losses, because the affected clusters are usually culled from the vines prior to
harvest, but there is no known cause or treatment. The general approach has been to
characterize berry shrivel (BS) so that it can be diagnosed and distinguished from other
problems, and to exploit the a unique resource at our Oakville Experimental Vineyard
where there are individual vines that are known to have exhibited BS each of the past 4 or
5 years. This past year was not a good (bad) year for BS; it was not hot; BS symptoms
were not widespread or early; and, bunch stem necrosis (BSN) was widespread,
complicating sampling and analysis. Nevertheless, progress was made on several fronts.
BS differs from BSN in that the rachis does not exhibit visual symptoms, and differs from
normal desiccation in that high Brix is not attained. Whether there is physiological
connection between BS and BSN should be investigated.

BS can be detected at and perhaps prior to veraison by measuring Firmness. This allows
us to select berries for study that will develop BS symptoms later. BS does not alter the
timing of veraison, but may delay the disruption of xylem conduits that normally occurs
at veraison. If this is found to be accurate, the sustained xylem connection may interfere
with phloem import of sugar. BS slows sugar accumulation from the outset of sugar
accumulation, but phloem transport is clearly active because Brix reaches values in the
high teens low twenties.

BS causes accelerated cell wall breakdown in the flesh (mesocarp) cells and results in a
jelly-like flesh. Extensive breakdown was apparent shortly after veraison, and therefore
the process is probably rapid. Growth and integrity of the skin of BS berries appears
normal. BS results in mesocarp cell death that is apparent during ripening and progresses as the
season progresses. The loss of cell viability and of cell wall may initiate near the
peripheral vasculature. Cell death may be related to the off flavors that BS is associated
with. BS is associated with high (wet) vine water status. This curious observation may indicate
that the vines are ?sick? in a systematic way. The condition could cause stomatal closure
or simply reduced canopy development, both of which could result in higher vine water
status. BS symptoms are similar to those created when the phloem to a cluster is girdled
completely at veraison. Thus, BS may result from a physiological disorder that causes
partial inhibition of phloem function upstream of the berry. We can now impose girdling
at various positions on the shoot and rachis, and test whether that results in other BS
symptoms such as loss of mesocarp cell wall and cell viability. If girdling ?causes? BS,
our search shifts away from the berry to the parent vine. Alternatively, girdling may
overcome the apparent partial blockage of phloem transport, and, thus, become a
temporary treatment for BS.