Acta Hortic. 1281. ISHS 2020. DOI 10.17660/ActaHortic.2020.1281.80 XXX IHC – Proceedings International on Symposium Understanding Fruit Tree Behaviour in Dynamic Environments Eds.: E. Costes et al. 609 Architectural factors affect fruit set in mango: evidence and modelling S. Persello 1,2 , I. Grechi 1,2 , F. Boudon 2,3 and F. Normand 1,2 1 CIRAD, UPR HortSys, 97455 Saint-Pierre, Réunion Island, France; 2 University of Montpellier, Montpellier, France; 3 CIRAD, UMR AGAP & INRIA Virtual Plants team, 34095 Montpellier, France. Abstract Fruit set, the transition from the flower to the growing fruit, is an essential step for fruit production. This process can be affected by environmental factors and by endogenous factors at the tree scale. The identification of these factors is important to improve cultivation practices and increase fruit set and fruit production. In this study, we focused on the identification of architectural factors affecting fruit set, with the mango tree as a case study. The hypothesis is that topological, phenological and morphological characteristics of the flowering terminal growth unit affect its fruit set rate. Two data sets describing the vegetative and reproductive development of mango trees in two orchards during two and three years, respectively, were analysed. Generalized linear models were used to test the effects of the characteristics of the terminal growth units on their fruit set rate. The effects of factors at a scale larger than the growth unit, such as the tree or the year were also tested. The date of burst of the terminal growth unit, i.e., its age at the time of flowering, its topological position, apical or lateral, and the number of inflorescences borne by the growth unit affected significantly its fruit set rate during most of the years. Fruit set rate was also affected by the year, by the orchard and by the previous year tree yield, suggesting that factors at the tree scale and environmental factors were involved in fruit set. These results are useful to design cultivation practices aiming to improve mango tree fruit set. They will be integrated in a model of mango fruit yield and quality at the tree scale to simulate more accurately fruit set and fruit production. Keywords: flowering, growth unit, inflorescence, Mangifera indica, tree architecture, yield INTRODUCTION Fruit set is the transition from the flower to the growing fruit and corresponds to a succession of processes, among which pollination, ovule fertilization and early fruit development. For a flowering plant, fruit set rate is a main component of the reproductive success during a given year, and therefore a component of yield for cultivated plants. It is particularly true for fruit tree species, for which fruit set rate may vary widely among individuals, cultivars, orchards and years (e.g., de Reffye et al., 1978; Davenport, 2009). A better knowledge of factors affecting fruit set could be a way to improve cultivation practices in order to maximize fruit yield. Factors affecting fruit set are exogenous and endogenous. Without detailing all the factors related to each individual process in fruit set, exogenous factors are mainly pollen availability, satisfactory pollination conditions (effective pollinators, wind) and weather conditions (temperature, rainfall). Endogenous factors are genetic, related to the reproductive system of the species and the level of self-compatibility of each individual, and physiological, involving hormones, carbohydrates and nutrients availability (e.g., Gó mez-Cadenas et al., 2000; Bermejo et al., 2018). Architectural traits may also affect fruit set rate. For example, fruit set rate of mango flowering growth units depends on growth unit topology and basal diameter (Normand et al., 2009). The identification of these factors is also important to integrate them in fruit tree models. Fruit tree models are scarce and related to temperate fruit trees like peach (L-Peach, Allen et al., 2005; Qualitree, Mirá s-Avalos et al., 2011), apple (MAppleT, Costes et al., 2008) or