Mimicking the fruit repression effect on Citrus flowering through continuous gibberellic acid treatments

In Citrus, flower intensity could be partially reduced or increased by applying gibberellins (GA3) or paclobutrazol (PBZ). However, under extreme harvest conditions, very high or very low treatments of these chemicals do not have any effect. Fruit inhibits flowering by activating CcMADS-box19 gene expression in the leaf, which blocks the inductive signalling preventing the expression of the CiFT3 gene. But signals that activate this repressive mechanism are unknown. The hypothesis of hormonal signalling is based on the inhibitory effect of GA3 on flowering. During the cold season, i.e., when flowers are induced, fruit changes colour by reducing active GA3 concentration in the flavedo. GA3 is basipetally transported to the shoots and the buds. To maintain GA3 concentration during the whole period of flower formation, vegetative shoots (those that always flower next season: OFF), and fruiting shoots (those that do not flower: ON) were treated weekly with GA3 during the floral bud inductive and differentiation periods. Flowering gene expression was measured in leaves and buds. Continuous PBZ treatments were used to avoid GA3 synthesis and promote flowering. GA3 and fruit show quantitative differences in their inhibitory effect. While GA3 partially reduced flowering, fruit prevented it. Fruit also prevented the promoting effect of PBZ. In our experiment, GA3 treatments reduced the expression of some the inductive and differentiation flowering genes, like CiFT3 and CiLFY, but did not promote the expression of CcMADS-19. Besides those effects, GA3 increased CcCEN gene expression.

Andrés Marzal won the ISHS Young Minds Award for the best poster presentation at the XIV International Citrus Congress in Turkey in November 2022.

Andrés Marzal, Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, 46022 València, Spain; Department of Agricultural, Food and Forest Sciences, University of Palermo, 90128 Palermo, Italy, e-mail: anmarbl5@etsiamn.upv.es

The article is available in Chronica Horticulturae