Variety-dependent responses of seeded vine cultivars to different growth regulators

Abstract: GA-levels and turnover rates during early berry development were much higher andlonger lasting in developing berries of Pinot gris compared to Sylvaner and were negativelyrelated to their sensitivity to exogenous applied GA3. Anthers and pollen are known to be majorsources of endogenous GAs during prebloom, and as such a higher pollen tube abundance couldbe responsible for higher endogenous GA levels during early berry development. Pinot gris andSylvaner showed the expected differences in pollen tube abundance that corresponded to theobserved endogenous GA levels. Furthermore, pollen tube analyses of a broad spectrum ofadditional cultivars with known GA-sensitivity support the hypothesis, displaying a broad rangeof pollen tube abundance that correlates negatively with the known sensitivity of the cultivars toGA3 applications.The observed variety-specific pollen tube abundance seems to lead to differentialdevelopmental patterns: postbloom, Pinot gris had no unfertilized ovaries while in Sylvaner up to35% of the ovaries were unfertilized. Furthermore, there were variety-specific differences in thedegeneration of ovules: Pinot gris had on average 3-4 fertilized ovules per ovary while Sylvaneronly had 1-2 fertilized ovules per ovary. However, during further berry development endospermdevelopment was aborted in about half of the ovules in Pinot gris, while in Sylvaner all fertilizedovules developed into seeds. Also in shattered berries the percentage of unfertilized ovaries wasmuch higher in Sylvaner than in Pinot gris. Altogether, variety-dependent effects were muchstronger than treatment effects.The results imply that a simple microscopic pollen tube analysis of varieties with hithertounknown gibberellin sensitivity might predict the sensitivity to exogenous GA3-treatmentincluding possible adverse side effects.