Use of Biostimulators to Reduce Abiotics Stress in Cucumber Plants (Cucumis sativus L.)

Applications of biostimulators are reported to reduce abiotic stress in plants. The physiological effect of these substances, however, is little investigated so far. In our previous experiments, we used a bioactive complex containing K-humate, LACTOFOL, and Bacillus subtilis FZB24 with positive effects on plant growth and yield. These experiments aimed to investigate the physiological effect of this biostimulating complex on the growth of Cucumis sativus cv. Indira cultivated in perlite. Two stress situations, suboptimal pH-level and temperature, respectively, were examined. The pH value was lowered from 5.8 to 4 for one week and the temperature was reduced to 60 degrees C for 3 h. Chlorophyll fluorescence was measured as an indicator for physiological effect of the biostimulating complex. Chlorophyll fluorescence measurement was conducted with a PAM-2000 measuring device using the saturation pulse method on dark adapted plants. For interpretation of chlorophyll fluorescence, the relationship Fv/Fm ("yield") was used as a parameter for efficiency of photosystem H (PSII). Before stress, yield ranged between 0.75 and 0.78. In response to pH and temperature stress, the yield dropped to 0.63. If the biostimulating complex was applied, yield dropped only slightly to 0.73. Several plant parameters such as plant shoot length, shoot weight, leaf weight, leaf area, root weight and root length were determined at the end of the experiment. The pH- and the temperature stress reduced the growth of the plants much more if no biostimulator was applied. Results show that there is strong correlation between green biomass of treated cucumber plants and their root mass. It can be assumed that the effect of stress reduction by use of this biostimulator complex is based mainly on enhancing the root growth.