Influence of intra-shoot trophic competition on shoot development in two grapevine cultivars (Vitis vinifera).

The effect of trophic competition between vegetative sources and reproductive sinks on grapevine (Vitis vinifera L.) shoot development was analyzed. Two international cultivars (Grenache N and Syrah) grown in pots, which were well watered, were studied. A large range of trophic competition levels was obtained by modifying the cluster loads per plant. An analytical breakdown of the branching system was used to analyze the effects of trophic competition. Phytomer production on the primary axis and the probability and timing of axillary budburst were not affected by trophic competition. However, the duration of development and leaf production rate for secondary axes were both significantly affected. The impact of trophic competition differed within the P0-P1-P2 architectural module, locally within the shoot and between cultivars. Trophic competition reduced the organogenesis of secondary axes most strongly close to clusters, on P1-P2 phytomers and in Grenache N. Based on these results, a modeling approach simulating sink strength variation and the local effects of sink proximity would be more relevant than a model considering only development as a function of thermal time or the global distribution of available biomass.