Advances in Citrus Flowering: A Review

Abstract

Citrus are polycarpic and evergreen species that flower once in spring or several times a year depending on the genotype and the climatic conditions. Floral induction is triggered by low temperature and water-deficit stress and occurs 2–3 months before bud sprouting, whereas differentiation takes place at the same time as sprouting. The induced buds develop single flowers or determinate inflorescences, so that vegetative growth is required at the axillary buds to renew the polycarpic habit. The presence of fruits inhibits sprouting and flower induction from nearby axillary buds in the current season. In some species and cultivars, this results in low flowering intensity the following spring, thus giving rise to alternate bearing. A number of key flowering genes act in the leaf (CiFT3, CcMADS19, etc.) or in the bud (CsLFY, CsTFL1, etc.) to promote or inhibit both flowering time and reproductive meristem identity in response to these climatic factors, the fruit dominance, or the age of the plant (juvenility). The expression of some of these genes can be modified by gibberellin treatments, which reduce bud sprouting and flowering in adult trees, and constitute the main horticultural technique to control flowering in citrus. This review presents a comprehensive view of all aspects of the flowering process in citrus, converging the research published during the past half century, which focused on plant growth regulators and the nutritional source-sink relationships and guided research toward the study of gene transcription and plant transformation, and the advances made with the development of the tools of molecular biology published during the current century.

Impacts of huanglongbing on fruit yield and quality and on flushing dynamics of Sicilian lemon trees

“…The vegetative shoots were classified in their stage of development ( Cifuentes-Arenas et al., 2018 ). The reproductive shoots were counted regardless whether they were single-flowered leafless, single-flowered leafy, multiflowered leafless or multiflowered leafy ( Agustí et al., 2022 ). Fruits were counted regardless of their size.…”

A bZIP transcription factor (CiFD) regulates drought‐ and low‐temperature‐induced flowering by alternative splicing in citrus

“…In the citrus industry, the main cultivars include sweet orange, grapefruit, mandarin orange, lemon, kumquat and trifoliate orange, and so forth (Wu et al, 2018). As woody fruit trees, the juvenile stage (the period from seed sowing to first flowering) of 6–8 years severely hinders traditional cross‐breeding of citrus (Agustí et al, 2022). Thus, the juvenile has attracted the attention of citrus breeders in the past few decades, and a large number of flowering homologous genes of model plants have been cloned and functionally characterized in citrus such as FLOWERING LOCUS T ( FT ), FLOWERING LOCUS C ( FLC ), SHORT VEGETATIVE PHASE ( SVP ), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 ( SOC1 ), APETALA1 ( AP1 ), and LEAFY ( LFY ) (Pillitteri et al, 2004; Nishikawa et al, 2007; Tan and Swain, 2007; Zhang et al, 2009; Agustí et al, 2020).…”

Microbiome diversity, composition and assembly in a California citrus orchard

“…The aim of this study was to characterize the citrus microbiome across five biocompartments (flush, flower, root, rhizosphere and bulk soil) during the floral development phase. At this stage, trees undergo drastic physiological shifts with respect to carbon reallocation, water dynamics and phytohormone production (Goldschmidt and Koch, 2017;Agustí et al, 2022) that are linked to significant shifts in microbial community assemblage (Ginnan et al, 2022). Both flower and flush are short-lived organs.…”