Streptomyces strains can improve the quality properties and antifungal bioactivities of tomato fruits by impacting WRKY70 transcription factor gene and nitrate accumulation.

The current study evaluated the effect of plant growth-promoting (PGP) strains of Streptomyces on yield, quality, and nitrate content of fruits, plant-microbe responses, and antifungal effect against blight disease caused by fungus pathogen Alternaria solani on tomato fruits in commercial greenhouse conditions. Greenhouse trials were done with four treatments including strains Y28, IC10, IT25, and commercial bio-fertilizer (Barvar NPK®) on tomato plants. In PGP treatments, the number of infected fruits significantly reduced (60%) compared to Barvar and control. Strain Y28 improved the quality of tomatoes more than other treatments. All three PGP treatments contained a higher level of total sugar concentration and antioxidant enzyme activities than Barvar and control. In contrast, PGP strains, especially Y28, significantly reduced nitrate accumulation (25%) compared to Barvar and control tomatoes. Streptomyces treatments induced more than a 20-fold increase in UDP and WRKY70 transcription factor gene expression relative to the control (P < 0.01). Based on the results, microbe-dependent plant defense induced by these strains is positively correlated to WRKY70 expression and nitrate reduction in commercial greenhouse conditions. These findings suggest that the commercial application of specific strains not only can illustrate an eco-friendly solution to induce resistance against fungal pathogens but also improve the quality properties of food plants with lower nitrate content.