Microbial inoculants as plant growth stimulating and soil nutrient availability enhancing options for cucumber under protected cultivation

Protected cultivation of vegetables is often hampered by declining nutrient availability in soil due to year-around farming, which in turn, leads to poor quality and yields, causing serious concern. Our study aimed towards evaluating the potential of novel biofilm formulations— Anabaena or Trichoderma as matrices with Azotobacter sp. as Anabaena–Azotobacter (An–Az) and Trichoderma-Azotobacter (Tr–Az) or together as Anabaena–Trichoderma (An – Tr), on the growth, physiological activities, yield, and changes in the profiles of soil microbial communities in two cultivars (cv. DAPC-6 and cv. Kian) of cucumber ( Cucumis sativus ). Photosynthetic pigments, evaluated as an index of growth showed two–threefold increase, while elicited activity of defense and antioxidant enzymes was stimulated; this facilitated significant improvement in the plants belonging to the inoculated treatments. Microbial biomass carbon and polysaccharides in soil enhanced by two–threefolds in treatments receiving microbial formulations. Available N in soil increased by 50–90% in An–Az and An–Tr biofilm inoculated treatments, while the availability of P and organic C content of soil improved by 40–60%, over control. PCR-DGGE profiles generated revealed signification modulation of cyanobacterial communities and cultivar-specific differences. Significant enhancement in leaf chlorophyll pigments, soil microbiological parameters and nutrient bio-availabilities along with positive correlation among the analysed parameters, and distinct profiles generated by PCR-DGGE analyses illustrated the promise of these novel inoculants for cucumber.