Factors Controlling Runner Formation in Strawberries

agronomy Factors Controlling Runner Formation in Strawberries

Abstract

Strawberry propagation relies predominantly on asexual reproduction via runner plants, making runners a critical organ for cultivation. Runners develop from axillary buds under specific environmental conditions. While long-day photoperiods and higher temperatures are key factors for inducing runner formation in most strawberry varieties, certain ever-bearing cultivars exhibit enhanced runner formation even under short-day conditions. Gibberellin is indispensable for runner bud outgrowth, with cytokinin and auxin synergistically regulating runner outgrowth. Genetically, Gibberellin biosynthesis genes strongly influence runner formation. Transcription factors such as LAM, SOC1, and HAN have recently been identified as key regulators. However, the genetic control of runner formation in strawberries, especially for cultivated octoploid strawberry cultivars, is not yet fully elucidated. This review synthesizes current knowledge on the environmental and genetic regulation of strawberry runner induction, providing a theoretical foundation for artificial control of runner formation.

One. Introduction

Stolons are stems that grow horizontally along the ground surface. They consist of two elongated internodes with a dormant bud at the middle node. A daughter plant and the next stolon segment develop from the second node. This linear growth pattern results in daughter plants spaced along the stolon, creating the appearance that they are "running away" from the mother plant. Hence, stolons are also called runners. Runners are important organs for asexual reproduction in plants; indeed, many species propagate using the daughter plants (transplants) produced on runners, including strawberry, potato, white clover, bermudagrass, and licorice.

Strawberry is an herbaceous perennial crop in the Rosaceae family. It is one of the most popular fruit crops around the world for its beautiful appearance, flavor, and health benefits. In two thousand twenty-three, global strawberry cultivation covered five hundred ninety-one thousand two hundred ninety-five hectares, with a yield of fourteen million seven hundred thousand nine hundred thirty-seven tons. As a result of this popularity, both cultivation area and production continue to increase steadily, driving extremely high demand for strawberry transplants. Consequently, strawberry propagation has attracted significant research interest. Strawberries can be propagated either sexually via seeds or asexually via runner plants. Asexual propagation is typically preferred because seed germination rates are very low and because cultivated strawberries are highly heterozygous, leading to character separation in seed-propagated offspring. Therefore, commercial production relies on runner propagation to maintain clonal fidelity and desired maternal traits. It should be noted that the number of runners produced by strawberries varies by cultivar, typically yielding fewer than fifty daughter plants per mother plant annually. This limitation necessitates substantial land resources for transplant production. Thus, understanding the regulatory mechanisms of runner formation is critical for efficiently producing high-quality transplants within limited land areas.

The strawberry plant features a highly compressed main stem (primary crown) with short internodes. Each node bears a single trifoliate leaf and an axillary bud (AXB) at the petiole-stem junction. The AXBs at the axils of leaves may remain dormant or develop new shoots. There are two kinds of axillary shoots in strawberry plants: runners and branch crowns (flowering shoot). AXB fate determination shapes plant architecture and occurs through two developmental phases: initiation and subsequent outgrowth. However, AXB initiation remains incompletely understood, particularly in rosaceous crops. Nevertheless, it is clear that AXB initiation and outgrowth are regulated temporally and spatially. Generally, the outgrowth of the AXB depends on its location on the primary crown, with the uppermost AXB having the highest priority for development into a runner or a branch crown. Furthermore, evidence from both wild and cultivated strawberries indicates that the development of AXBs into either runners or branch crowns is a genetically distinct and mutually exclusive process. The predominance of one developmental pathway over the other is intricately regulated by genetic and environmental factors. In light of this, this review analyzes these regulatory mechanisms to advance understanding of runner formation in strawberry.