The Complex Interactions Between Flowering Behavior and Fiber Quality in Hemp

Abstract

Hemp, Cannabis sativa L., is a sustainable multipurpose fiber crop with high nutrient and water use efficiency and with biomass of excellent quality for textile fibers and construction materials. The yield and quality of hemp biomass are largely determined by the genetic background of the hemp cultivar but are also strongly affected by environmental factors, such as temperature and photoperiod. Hemp is a facultative short-day plant, characterized by a strong adaptation to photoperiod and a great influence of environmental factors on important agronomic traits such as “flowering-time” and “sex determination.” This sensitivity of hemp can cause a considerable degree of heterogeneity, leading to unforeseen yield reductions. Fiber quality for instance is influenced by the developmental stage of hemp at harvest. Also, male and female plants differ in stature and produce fibers with different properties and quality. Next to these causes, there is evidence for specific genotypic variation in fiber quality among hemp accessions. Before improved hemp cultivars can be developed, with specific flowering-times and fiber qualities, and adapted to different geographical regions, a better understanding of the molecular mechanisms controlling important phenological traits such as “flowering-time” and “sex determination” in relation to fiber quality in hemp is required. It is well known that genetic factors play a major role in the outcome of both phenological traits, but the major molecular factors involved in this mechanism are not characterized in hemp. Genome sequences and transcriptome data are available but their analysis mainly focused on the cannabinoid pathway for medical purposes. Herein, we review the current knowledge of phenotypic and genetic data available for “flowering-time,” “sex determination,” and “fiber quality” in short-day and dioecious crops, respectively, and compare them with the situation in hemp. A picture emerges for several controlling key genes, for which natural genetic variation may lead to desired flowering behavior, including examples of pleiotropic effects on yield quality and on carbon partitioning. Finally, we discuss the prospects for using this knowledge for the molecular breeding of this sustainable crop via a candidate gene approach.

A high-throughput segregation analysis identifies the sex chromosomes ofCannabis sativa

“…However, legalisation of marijuana is so recent that very few biotech tools have been developed for high THC-producing C. sativa cultivars (Yeager 2018). Interest on hemp is also increasingly attractive as crop for the sustainable production of fibres and oils (Andre et al 2016;Salentijn et al 2019). Hemp cultivars usually have a low level of THC and can legally grow in many countries where marijuana is illegal.…”

Genetic Variability of Morphological, Flowering, and Biomass Quality Traits in Hemp (Cannabis sativa L.)

“…Hemp is a short day plant, and its flowering time is influenced by changes in the photoperiod regime (Amaducci et al, 2012). In locations where the shift from long-day toward short-day photoperiod regimes occurs early, hemp plants flower early, whereas in locations where the shift occurs later, the critical photoperiod for flowering is reached later (reviewed in Salentijn et al, 2019). This behavior affects plant development because plants accumulate biomass during the vegetative growing period, but nutrients are shifted from the production of stem, leaves, and roots toward the production of flowers and seeds around the onset of flowering.…”

Elucidating the Genetic Architecture of Fiber Quality in Hemp (Cannabis sativa L.) Using a Genome-Wide Association Study

“…The large variability of the hemp panel enables further mapping studies for hemp traits that still remain poorly studied. The hemp panel and the methodology developed in this study are a great value to extend the genetic basis of many traits beyond cell wall traits, such as flowering time and sex determination (Salentijn et al, 2019) and understand their interaction with fiber quality traits. Those studies would also provide more molecular breeding tools to accelerate the development of new hemp cultivars with improved fiber quality.…”

“…Different genetic approaches can be performed to study its genetic basis, such as reverse genetics (candidate gene approaches) and forward genetics (genetic mapping studies). Salentijn et al (2019) reviewed the state of art of candidate gene studies for fiber quality in hemp. Briefly, most of the reported genes have a function in the lignin metabolism or code for phytohormones involved in plant development with a possible effect on lignin (Salentijn et al, 2019).…”

“…Salentijn et al (2019) reviewed the state of art of candidate gene studies for fiber quality in hemp. Briefly, most of the reported genes have a function in the lignin metabolism or code for phytohormones involved in plant development with a possible effect on lignin (Salentijn et al, 2019). However, many different metabolic pathways are involved in the biosynthesis and regulation of the cell walls.…”