Effect of thidiazuron on the Humulus lupulus L. clonal micropropagation

The diverse effects of thidiazuron on the anatomical, morphological, and physiological characteristics of plants require careful selection of optimal regimes and dosages for clonal micropropagation tailored to each species. This article examines the impact of thidiazuron on Humulus lupulus L. during the shoot multiplication phase, utilizing concentrations ranging from 0.1 to 0.5 mg L−1 in increments of 0.1 mg L−1. The basal Murashige and Skoog medium (MSm) was supplemented with 0.1 mg L−1 of 3-indoleacetic acid (IAA) and 20 g L−1 of glucose. The growth and development of regenerant plants were evaluated using a novel scale based on the timing of morphological structure formation. Regenerant plants cultured on all variants of the thidiazuron-supplemented medium exhibited delayed development compared to the control group. Specifically, 62.8% of the regenerants were clusters of de novo shoots emerging from the explant nodes, while only 10.6% developed more robust shoots, characterized by small leaves and shortened internodes, indicative of chlorosis. Upon transferring these conglomerates to MSm and MSm supplemented with 0.1 mg L−1 IAA, growth inhibition was observed, with development rates more than 1.5 times slower than those in the control group. Some regenerants displayed signs of overhydration and shoot deformation, resulting in non-viability. Therefore, for Humulus lupulus L., it is suggested that thidiazuron should be used solely for short-term stimulation of multiple de novo shoot proliferation in genotypes exhibiting low reproduction rates.