Clonal Testing of Winegrapes in the San Joaquin Valley

Syrah grapevines may produce good to excellent quality fruit for red wine in the San
Joaquin Valley so this variety may elevate the reputation of valley winegrapes if care is
taken to maximize fruit quality. To help ensure optimal fruit quality and yield, growers
should select the clone or clones that are best suited to the Valley?s climate. Many new
selections of Syrah have recently been made available from Australia and France, but
their relative performance in the San Joaquin Valley is not yet known. Thus, we are
comparing the yield, yield components, fruit composition, and susceptibility to sour rot,
of ten selections of Syrah in a trial at the Kearney Agricultural Center, Parlier. After two
years, it is evident that there is considerable variation among the Syrah clones. The fruits
of clone 1 are the earliest to mature; at harvest their fruit have the highest soluble solids,
and among the highest pH and lowest titratable acidity, of the clones tested. In contrast,
fruits of clones 100, 174, 300, and 525 had the lowest soluble solids of the clones tested,
though the pH and TA of their juices was similar to that of many other clones. Clones 03
and 100 produced 15 to 35%greater yields than the other selections because they had the
most, and among the heaviest, clusters of fruit. Clones 03 and 100 were moderately
susceptible to sour rot, having higher sour rot incidence than Shiraz 01, Shiraz 03, Shiraz
07, and Syrah 99. Syrah 525 had far higher sour rot incidence than the others perhaps, in
part, due to its high number of berries per cluster. Clone 99, in this early stage of
evaluation, is one of the most promising selections because it has relatively good yields,
is somewhat resistant to sour rot, and has fruit composition that is comparable to that of
many other clones. Though production of grapes for high quality table wines is
increasingly important in the San Joaquin Valley, there remains a market for generic
white wine grapes, for concentrate, brandy, and generic wines and blends. To insure
profitability of this commodity, growers must develop vineyards capable of producing
high yields of fruit at low cost. To aid these efforts, four white winegrape varieties
having high yield potential, Colombard, Grenache Blanc, Triplett Blanc, and 182-4 were
compared. Colombard and Grenache Blanc matured about three weeks earlier than
Triplett Blanc and 182-4, with similar yield and fruit composition at harvest. However,
Colombard is much more susceptible to sour rot than Grenache Blanc, or Triplett Blanc.
All things considered, Grenache Blanc was superior to the other varieties due to its
earliness and lower susceptibility to sour rot.