Microalgae produce many secondary metabolites that are biologically active, including compounds that inhibit microbial growth. These could potentially function as biofungicides. The first selection criteria for potential strains suitable in the phytosanitary market is good in vitro inhibition of growth against specific phytopathogenic fungi and oomycetes and higher biomass productivity rates. In the present study, water extracts were prepared from 280 strains comprising of 33 Cyanophyceae strains (13 genera), 157 Chlorophyceae strains (29 genera), 80 Trebouxiophyceae strains (19 genera), 5 Klebsormidiophyceae strains (1 genus) and 1 Zygnematophyceae strain. These were tested in vitro against 6 phytopathogenic fungi and 3 phytopathogenic oomycetes. In total, 45% of the species had mycelial growth inhibitory activity against at least one pathogen. Cyanobacteria had the highest “hit-rate” (64%), followed by the Chlorophyceae (49%) and Trebouxiophyceae (30%). Water extracts of 19 strains had fungicidal and/or oomyceticidal activity – these were predominantly Cyanobacteria. The Cyanobacteria displayed a wider spectrum of inhibition with five strains being active against three or more phytopathogenic strains. Trichormis variabilis MACC-304 and Tolypothrix tenuis MACC-205 had inhibitory activity against 6 phytopathogens and Nostoc linckia MACC-612 inhibited 4 phytopathogenic strains. Each Chlorophyta strain was only active against 1-2 strains. However, the daily productivity rates of Cyanobacteria were significantly lower than Chlorophyta strains. Further investigation of 15 Nostocales species (Nostocaceae, Tolypothrichaceae and Calotrichaceae) showed the Nostoc species generally had significantly lower biomass generation compared to other Nostocacaeae strains. The most promising strain was Tolypothrix tenuis MACC-205 which had the most potent, broad spectrum fungal and oomyceticidal inhibitory activity as well as significantly higher daily biomass productivity rates. Thus, Cyanobacteria can potentially be developed as an effective agricultural tool for environmentally-friendly disease management.

The rhizomania is known in Hungary since 1982. The causal agent, Beet necrotic yellow vein benyvirus (BNYVV) is transmitted by a soil-borne fungus Polymyxa betae Keskin. A field experiment was done under rhizomania infested and non-infested conditions to compare the yield parameters of five tolerant and four sensitive sugar beet hybrids. Tolerant varieties produced higher root yield under rhizomania infected conditions. The root yields of the sensitive varieties were similar to the tolerant ones on the uninfested field, but the root mass of some tolerant varieties exceeded the production of the former group. Subsoiling was carried out in two strips of a heavily infested field, while conventional soil cultivation was done on the other parts. There was not any other difference in the cultivation of the treated and control areas. Sugar beet root samples were collected at the time of harvesting from the subsoiled and control plots. Beet necrotic yellow vein virus (BNYVV) infection was tested by means of ELISA. Virus content, yield and yield parameters of samples were compared. There were no significant differences in virus infection between sugar beet roots derived from subsoiled and untreated plots. Ratio of BNYVV infected plants was about 90% in both areas. However, yield and yield parameters showed remarkable difference. Root yield of treated plots, calculated from average individual root weight and 80,000 plant/ha plant density exceeded by 140% the yield of control. Sugar content was 2.6% higher and the harmful non-sugar content was lower on the subsoiled plots. Owing to the favourable chemical and technological value of beet the white sugar content was approximately three-times higher on the treated area.