Abstract
The negative effects of fruit production during one cycle on reproduction during the following cycle are generally explained by two complementary processes: hormone synthesis and carbohydrate mobilization. Our study focused on mango (Mangifera indica L.) for which it has been shown that reproduction decreases and delays vegetative bud outgrowth. This, in turn, affects flowering and fruiting in the following cycle. Vegetative growth therefore plays a pivotal role in irregular fruit production patterns across consecutive years. Our aim was to decipher the respective roles of hormones and carbohydrates on the negative effects of reproduction on vegetative growth. We analyzed the changes in various hormone (auxin, cytokinin, abscisic acid) and carbohydrate (glucose, sucrose, starch) concentrations in terminal axes with vegetative and reproductive fates of two mango cultivars, Cogshall and José, characterized by different bearing patterns, across consecutive phenological periods during a growing cycle. Auxin concentrations were high in inflorescences, fruit peduncles and axes bearing inflorescences or fruit, suggesting auxin-induced inhibition of vegetative bud outgrowth in the flowering and fruiting axes. Moreover, growing fruits, which are strong sink organs, depleted carbohydrates from non-fruiting axes. During vegetative growth, this starch depletion probably contributed to decreasing the probability of and to delaying vegetative bud outgrowth of reproductive axes for Cogshall, and of reproductive and nonreproductive axes for José. Starch dynamics in quiescent and flowering growth units during early fruit growth and their starch concentrations at fruit maturity differed between the two cultivars, presumably in relation to the observed contrasted crop loads and/or to differences in photosynthetic capacity or carbohydrate allocation. These differences between the two cultivars in terms of starch concentration in terminal axes during vegetative growth could partly explain their different bearing patterns.
Highlights
Heavy fruit load reduces owering and fruiting in the following year in several fruit tree species (Muñoz-Fambuena et al 2011, Guitton et al 2012, Samach and Smith 2013)
Our study showed that the relationships between reproduction and vegetative bud outgrowth in mango were better explained by the dynamics of hormones and carbohydrates together rather than by one or the other considered independently
The inhibition of vegetative growth on owering and fruiting growth unit (GU) between owering and fruit maturity appeared to be predominantly driven by indole-3-acetic acid (IAA), and carbohydrates might play a role at fruit maturity
Summary
Heavy fruit load reduces owering and fruiting in the following year in several fruit tree species (Muñoz-Fambuena et al 2011, Guitton et al 2012, Samach and Smith 2013) This phenomenon is referred to as alternate or irregular bearing, depending on the bearing pattern over consecutive years (Monselise and Goldschmidt 1982, Goldschmidt and Sadka 2021). This could be a direct e ect of current fruit load on oral induction when the latter occurs during fruit growth, i.e., in most temperate fruit trees (Chan and Cain 1967, Wilkie et al 2008, Samach and Smith 2013). These ndings in mango as well as in some other species (Hasegawa and Takeda 2001, in forest trees; Lauri and Trottier 2004, in apple) strongly support the idea that vegetative growth between two consecutive reproductive periods plays a pivotal, but insu ciently known, role in irregular bearing
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