Photoperiodic dependence of the morphological and anatomical structure of the above-ground vegetative organs of flax (Linum usitatissimum L.)

The stem length, the type of branching and the development of bast fiber layer in flax have are great economic importance. Traditionally, within the flax species, the fiber, intermediate, shot-stem and creeping semi-winter flaxes are segregated. Between these morphotypes, there are transitional forms. The duration of photoperiods during vegetation is one of the main factors that modify the morphology of flax. An analysis of previously published articles and own researches conducted in 2012-2016 on the basis of FGBNU VNIIMK, Krasnodar, showed that over the last century, the views on the morphology and anatomy of epiterranean vegetative organs in intraspecific varieties of flax have undergone a number of changes. Because of the high photoperiodic sensitivity, previously considered as taxonomically isolated intermediate flax form, with increasing length of the day, freely passes into short-stem forms. Conversely, against the background of shortened photoperiods, intermediate flaxes acquire a fiber phenotype. This confirms the reasonableness of the decrease in the taxonomic gradation of fiber, intermediate and short-stem branched flaxes from isolated species and interspecific hybrids to intraspecies within the species of L. usitatissimum L. The morphological differences in a structure of epiterranean vegetative organs of these varieties are apparently determined only by complexes of genes that encode different photoperiodic responses to the duration of the light period. Anatomical studies of the stem structure in fiber and intermediate flaxes also showed that spinning and oilseeds respond equally to the change in the day length. In long-day conditions, the thickness of the xylem wood is increased, and in short-day it decreases. The tendency to increase the bast fiber simultaneously with the increase in the wood layer under long day conditions, both in fiber and intermediate flaxes, is revealed.