Effect of bacterium Pseudomonas fluorescens and low fungicide dose seed treatments on parasite fungus Aphanomyces cochlioides and sugar beet yield and quality

Effect of sugar beet seed inoculation with a bacterium Pseudomonas fluorescens and treatment by fungicides Thiram 42-S and Dithane S-60 with and without seed inoculation aiming to control Aphanomyces cochlioides - root decay agent was studied. The trial lasted for three years on two soil types (Mollic Gleysols and Eutric Cambisols). The following parameters of sugar beet yield and quality were investigated: root yield, sugar content, sugar in molasses, sugar yield as well as percentage of the infected and decayed plants as a consequence of parasite fungus infestation. The highest average sugar beet root yield was obtained in the variant of the seed treated with fungicide Thiram 42-S and inoculated with bacterium P. fluorescens (85.15 t/ha). However, there were no statistically significant differences (P < 0.05) between the above-mentioned variant and the one with seed inoculated only with bacterium P. fluorescens (84.63 t/ha). The highest mean sugar content of 16.39% was also accomplished during the three-year investigation in the variant of the inoculated seed treated by fungicide Thiram 42-S. All other variants accomplished statistically very significantly lower values of this parameter. The same variant was characterized by the highest mean sugar yield value (12.79 t/ha) on both soil types. Namely, an average sugar yield of the variants inoculated with bacteria was 11.22 t/ha and by 44.22% higher compared to an average yield of non-inoculated variants. The highest percent of the infected and decayed plants (average value on both soil types in the three year investigation) was reported in the control variant (28.92% infected and 25.00% decayed plants) whereas the lowest one was detected in the variant of the seed inoculated with bacterium P. fluorescens in combination with low dose of fungicide Thiram 42-S (4.70% infected plants and 2.88% decayed plants). An average percent of the infected plants inoculated with bacterium P. fluorescens was 9.13% whereas the aforesaid value of the plants infected with parasitic fungus A. cochlioides in non-inoculated variants was by 146.00% higher being 22.42%.