Growth disorders and phenotype variability in phytotron‐cultivated barley

In continuation of previous studies, four barley varieties were included in an experiment to test the influence of photo‐ and thermoperiod on plant development and phenotypic variability. Using the short photoperiod of 12 hours, anomalies of development were especially frequent in Ingrid and Kristina barley and the line 8004‐37 of Rupal barley. Photoperiods of 24 and 16 hours gave but few major disturbances. All varieties had a higher number of nodes and internodes in short‐day than in long‐day cultivation. The growth disorders appeared in the upper part of the stem at the transition zone of the vegetative and generative system. False flag‐leaves were common. Basal rachis internodes frequently became greatly elongated. Secondary shoots were formed from the last stem node, from ordinary and extra collars as well as rachis nodes, including also the origin of secondary spikes. The disorders were less severe in Bonus and Rupal barley 8004‐1. The anomalies implied the end stage of a gradually increasing level of variability with an ultimate developmental disorganization, generally not found at optimal conditions but common in short photoperiods. “Phenetics”, a concept applied by Mayr, illustrates and explains the dynamic pattern of genotype reactions to changing environments.