Pseudomonas putida P3-57 induces cucumber (Cucumis sativus L.) defense responses and improves fruit quality characteristics under commercial greenhouse conditions

The possibility of chemical fertilizer residues in cucumber has raised concerns about the consumption of this beneficial fruit. Although very good studies have been reported on the effect of growth-promoting bacteria on increasing the health of cucumber plants, their performance in commercial greenhouse conditions has been less studied. A two-year study was conducted to evaluate the effect of P. putida strain P3-57 with 100 % or 70 % of the recommended amount of NPK fertilizers on cucumber fruit yield and quality compared to Barvar NPK (R) commercial biofertilizer under commercial greenhouse conditions. The 30 % reduction in chemical fertilizers reduced yield and overall fruit acceptance score in the sensory evaluation test. Plant treatment with P3-57 or Barvar had no significant effect on yield but when 70 % of chemical fertilizers were used, they increased the quality of cucumber due to the increase in the score of some sensory traits. P3-57-100% had the highest overall acceptance score, which was associated with increased aroma, flavor and fruit juice, and the lowest levels of nitrate, Zn, Mg, Mo, Sr, Ba and Li. Also, the concentration of protein and CAT activity of fruits was higher compared to control-100 % and Barvar-100 %. Evaluation of CAT, APX and PDX activity and expression of PR1-1a, GLU, APX, CHIT, LOX and PAL showed that P3-57-100 % and Barvar-100 % stimulate plant immune system through ISR/SAR and SAR pathways respectively. Based on the results of this study, strain P3-57, as a biostimulator that increases cucumber quality, has great potential to enter the market.