A new autoclave extract from Anabaena minutissima for seed priming improves tomato plantlets growth and protects against soilborne pathogens

This study assessed the effectiveness of the treatment of tomato seeds with an aqueous extract of the dried biomass of the microalga Anabaena minutissima in protecting the plants from diseases caused by soilborne pathogens like Rhizoctonia solani and Pythium ultimum. The extract, obtained by an autoclave-assisted method at 100 °C, was rich in proteins and carbohydrates (56.6 and 26.9% of total solids). Preliminary tests were performed revealing: i) a moderate direct activity toward pathogen in vitro growth, with ± 9% stimulation/inhibition, depending on the pathogen; ii) a stimulatory/inhibitory activity toward seedling growth, depending on the dose; iii) no effect on the mycelial growth by root exudates of treated plantlets. Then, a greenhouse experiment was set up to test the response of tomato plants in substrates artificially inoculated with the single pathogens, after seed treatment with the extract at different doses (0, 2.5, 5, and 10 mg mL^-1). The treatment generally increased the percentage of standing plants and restored plant development up to the level of healthy controls. Moreover, the disease incidence and severity progressively reduced at increasing doses. Finally, the seed treatment significantly increased some markers of induced systemic resistance like endochitinase and glucanase activity, in hypocotyls of 14-day-old seedlings, compared to non-treated controls. Besides, the treatment increased epicotyls’ carotenoid and chlorophyll a and b content. Overall, these results demonstrate that seed priming with A. minutissima aqueous extract is a promising eco-friendly tool to ameliorate tomato plant responses towards soilborne pathogens, stimulating plant growth and activating induced resistance mechanisms.