Cabernet Sauvignon and Muscat of Alexandria were less tight than the other cultivars and were below the methodology threshold of 0.0005 N.
Cluster tightness was also quantified for the seven cultivars. Cabernet Sauvignon and Muscat of Alexandria berries were more susceptible than expected, considering the low level of disease usually observed in the field. The slope of the inoculum density-disease incidence response, used as an index of susceptibility, ranged from 0.07 for Emperor to 2.13 for Muscat of Alexandria in 1988. The percentage of diseased berries was determined after 7 days at 25 C and 95% relative humidity. Cabernet Sauvignon, which had a loose cluster, dried at a higher rate than did Barbera, Colombard, or Semillon, which had tighter clustersĭetached mature grape berries from seven cultivars were inoculated with conidia of Botrytis cinerea over a range of 10(2)-10(6) conidia per milliliter. The rate of surface water loss per hour was also determined for each of the clusters. The number of berries per centimeter of rachis, the component most commonly used by viticulturists to estimate cluster tightness, was least important in its contribution to cluster tightness (path coefficient of 0.09). Cluster weight and the ratio of interior to exterior berries contributed most to cluster tightness, with path coefficients of 0.35 and 0.25, respectively. Components of cluster architecture were measured and their respective contribution to cluster tightness determined by path analysis. The cultivars most severely affected by bunch rot in the field had the tightest clusters, while cultivars with loose clusters were least affected in the field. Detached mature grape berries from seven cultivars were inoculated with conidia of Botrytis cinerea over a range of 10(2)-10(6) conidia per milliliter.
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