Control of Flowering and Runnering in Strawberry

Abstract

Strawberry flowering physiology has engaged the interest of researchers for almost a century after the initial reports demonstrating the photoperiodic control of flowering and vegetative reproduction through stolons called runners. Most strawberries possess a seasonal flowering habit with flower initiation occurring under short days in autumn and flowering during the following spring. Also perpetual flowering genotypes are known in diploid woodland strawberry (Fragaria vesca L.) and octoploid garden strawberry (F. × ananassa Duch.), and recent research have shown that this trait has evolved independently in different species. Studies in the perpetual flowering mutant of woodland strawberry led to the identification of TERMINAL FLOWER1 (FvTFL1) as a major floral repressor causing the seasonal flowering habit in this species and demonstrated that recessive mutation in this gene leads to perpetual flowering. This breakthrough opened an avenue for molecular understanding on the control of flowering by different environmental signals. Different loci control perpetual flowering in garden strawberry including one dominant major locus and additional environmentally regulated epistatic loci. The major gene is called Perpetual Flowering Runnering (PFRU) because it also reduces the number of runners. Growth regulator applications initially demonstrated the role of gibberellin in the control of runner formation, and molecular understanding on the role of gibberellin biosynthesis and signaling in this process has started to emerge. Here, we present current understanding and major open questions on the control of flowering and runnering in strawberries. In order to understand the control of flowering in the context of perennial growth cycle, we also discuss current knowledge on the control of dormancy.

High density linkage map construction and QTL mapping for runner production in allo-octoploid strawberry Fragaria × ananassa based on ddRAD-seq derived SNPs

“…In SF genotypes, the period of flowering is followed by runnering when primary stolons emerge from the basal axillary buds that elongate and give rise to new clonal plants at varyingly spaced nodes. Whereas, in PF genotypes, these sexual and asexual reproduction period overlaps in summer 4,5,9 . Evidences from both wild and cultivated strawberry show that flowering and runnering are genetically distinct but mutually exclusive processes as the predominance of one over the other is intricately related with genetic and environmental factors 3–5,7 .…”

“…Whereas, in PF genotypes, these sexual and asexual reproduction period overlaps in summer 4,5,9 . Evidences from both wild and cultivated strawberry show that flowering and runnering are genetically distinct but mutually exclusive processes as the predominance of one over the other is intricately related with genetic and environmental factors 3–5,7 . Longer days and higher temperatures promote runnering in SF genotypes, which in short and cooler days produce branch crowns that are differentiated to inflorescence and hence, increases flowering and crop productivity 5,10,11 .…”

“…Cultivated strawberry is favored across the globe for its characteristic appearance, flavor, nutritional qualities and health benefitting anti-oxidative properties 1 which is evident by the continual increase in the cultivation and production of the crop in the last two decades (FAOSTAT 2018). Moreover, strawberry is an interesting model crop due to its unique reproductive dynamics, having intricate relationship between sexual reproduction via flowering and asexual reproduction via runnering, which is greatly modulated by environmental cues 2–5 . Strawberry cultivars were characterized as seasonal flowering (also known as short-day, June bearing or non-remontant) or perpetual flowering (also known as day-neutral, long-day, everbearing, rebloomer or remontant) based on the flowering response that heavily depends on photoperiod and temperature 6,7 .…”

“…Evidences from both wild and cultivated strawberry show that flowering and runnering are genetically distinct but mutually exclusive processes as the predominance of one over the other is intricately related with genetic and environmental factors 3–5,7 . Longer days and higher temperatures promote runnering in SF genotypes, which in short and cooler days produce branch crowns that are differentiated to inflorescence and hence, increases flowering and crop productivity 5,10,11 . Higher temperatures also increase runnering in PF genotypes, however, the effect of photoperiod were found to be variable by different experiments 3,12–14 .…”

A Long-Day Photoperiod and 6-Benzyladenine Promote Runner Formation through Upregulation of Soluble Sugar Content in Strawberry

“…Strawberry is a rosette-forming plant, with short stems that are also called the primary crown. At the base of each leaflet along the primary crown, there is an axillary meristem (AXM), and these AXMs can either develop into runners and branch crowns, or remain dormant [ 3 ]. A high number of branch crowns means more inflorescence because only the shoot apical meristem (SAM) can develop an inflorescence [ 4 ].…”