International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The unsustainable use of agrochemicals to protect the agricultural crops and increase the yield is one of the reasons for contamination of soil, fresh- and groundwater. As an alternative to chemical fertilizers and pesticides, biofertilization with plant growthpromoting rhizobacteria (PGPR) can cause increasing of yield, diseases and pests resistance. The aim of the current study is to evaluate the potential of some bacterial isolates to stimulate plant growth of young melon plants of two commercial Bulgarian melon cultivars. Melon seedlings at cotyledon stage are inoculated with the bacterial isolates. 35 days after inoculation, the main growth parameters of the plants are measured: fresh and dry weight of shoots, number of leaves, length and thickness of the steam and total leaf area. The obtained results reveal that all of the tested bacterial isolates insignificantly increase the sixth plant growth indexes of Pobeditel melon plants but the best results are observed with B 92 treatment. Plants from Hybrid 1 genotype are positively and significantly influenced by all bacterial isolates. The best results are observed with B 86 treatment – up to 2.7-fold increase in total leaves area and up to 2.4-fold increase in stem length. Plants treated with B 86 also have 50-70% higher shoot fresh and dry weight, 24% thicker stems and 30% higher number of leaves compared to non-inoculated controls. Some of the tested bacterial isolates especially B92 and B97 stimulate the absorption and utilization of major nutrients as N and P.

Soil salinity is one of the main limiting factors for the plant growth and productivity. Response of three garden pea cultivars (Mira, Zornitsa and Ran 1) to salt stress in in vitro and in vivo conditions was studied. The in vitro stress was induced by adding of 0 (nontreated control), 50, 100 and 200 mM NaCI in culture medium. After two weeks the germination and seedling emergence rate were not significantly affected by 50 mM NaCl. In culture medium containing 200 mM NaCl only 13.3 – 43.3% of the seeds developed to the plants. The data indicated that increasing NaCl level the shoot and root lengths, and plant fresh weight were significantly reduced. In in vivo condition, such clear differences between the tested NaCl concentrations were not observed. Nevertheless, the applied salt stress more strongly affected the shoot fresh weight and root length than stem length. Among the three tested genotypes cultivar Zornitsa was the most tolerant one, proved in both in vitro and in vivo experiments.