Fruit abscission in cv. Grenache N.: what are the roles of extreme temperatures and plant carbon gain?

Abstract

Flowers and berries abscission (coulure) can lead, during some vintages and for sensitive cultivars, to dramatic yield losses with detrimental impacts on the wine industry. Many exogenous and endogenous factors are known to favor defaults in reproductive development and coulure, among which extreme temperatures and carbon imbalances play a major role. However, the specific impacts of temperature and carbon status on the failure of early reproductive development for cv. Grenache N. in Southern France remain unknown. Four experiments were conducted in pot (2016) on the clone 362 of Grenache N., which is considered as a susceptible clone to coulure. Contrasted day/night (D/N) temperature treatments of varying durations (0°C to 15°C during the night, 10°C to 33°C during the day) and one anti-transpirant treatment aimed at reducing the carbon status of the plant were imposed over the meiosis to flowering period. The reproductive performances (rates of fruit setting, abscission and millerandage), as well as the net gain of carbon calculated from the photosynthesis and respiration rates, or related-proxies (shoot vigor) were evaluated. The abscission of young berries reached at least 60% for all treatments. The rate of fruitset was the lowest and the rate of millerandage the highest when a prolonged period of cold temperatures was imposed around female meiosis (2 weeks at 10/10°C D/N). The net carbon gain at this stage, ranging from 0.02 to 0.85 mol m^-2 s^-1 for all treatments, was positively correlated to the number of flowers and berries and negatively correlated to the rate of millerandage. These variables were also correlated to the shoot vigor beneath the inflorescence at the same stage. These preliminary results allowed us to quantify the impacts of temperature and carbon constraints on early berry development. A simple and non-destructive indicator of shoot carbon status related to reproductive performances was proposed.