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.
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