Bioactive effect of cyanobacteria and calcareous algae mixture in bioassays and on potato growth and yield1

ABSTRACT The growth-promoting effect of the micronized calcareous algae Lithothamnion sp. is related to the presence of humic acid and its bioactive auxin-like effect, characteristic of humic substances, whereas the plant growth-promoting effect of the microalgae (cyanobacteria) Arthrospira platensis (Spirulina platensis) has been attributed to the presence of L-amino acids and polyamines in its biomass. The present study aimed to identify the possible synergistic bioactive effect of a mixture of both sources (micronized Lithothamnion and A. platensis biomass) in bioassays and in the field, with foliar application, on organic potato (Solanum tuberosum L.) cultivation. Four bioassays were carried out to evaluate the root growth of Vigna radiata, as well as the expansion of Solanum lycopersicum hypocotyls, Cucumis sativus cotyledons and V. radiata hypocotyl-radicle axis. Subsequently, a field experiment was conducted in an organic system with foliar application to potato plants. The bioassays showed the bioactivity of the calcareous algae and of the cyanobacteria, and their combination, promoting biometric and metabolic changes, increasing the potato yield and tuber sugar content. Thus, the mixture of micronized Lithothamnion with A. platensis biomass can be a novel natural input to sustainably improve potato growth and yield.