Epiphytic and endophytic bacteria were isolated from healthy cucumber plants, collected in several counties of Pernambuco State, Brazil, and evaluated for seedling growth promotion under greenhouse conditions. Three bioassays were performed. In the first, 93 strains were tested; in the second, 32, and, in the third, eight from cucumber plus 10 bacterial epiphytic strains from other crops were used. The cucumber seeds were bacterized by immersion in the bacterial suspension adjusted to A580 = 0.7, sown in polystyrene trays filled with organic substrate and analyzed ten days after sowing in relation to shoot (MSPA), root (MSR), and total (MST) dry matter. In the third bioassay the epiphytes PEP52, PEP8, PEP82, PEP91, and C22 were selected because they significantly (P=0.05) elevated MSR and MST in relation to the control reaching higher values than 70 and 40%, respectively. After compatibility tests the five isolates applied separately and in mixtures efficiently increased the index of MSPA, MSR, and MST in cucumber seedlings, without differing among them. It is worth noticing that PEP81 (Bacillus amyloliquefaciens) and PEP91 (Enterobacter cloacae) increased 55.5 and 34.5% (MSPA), 42.9 and 37.2% (MSR), and 41.6 and 34.0% (MST), respectively. The production of indolacetic acid, hydrogen cyanide, phosphate solubilization and changes in foliar levels of N, P, K, Ca, and Mg were evaluated as putative mechanisms of action for theses isolates, but they showed negative results. Seed bacterization with B. amyloliquefaciens PEP81 and E. cloacae PEP91 could improve quality of cucumber seedlings.
Cucumis sativus; Enterobacter cloacae; Bacillus amyloliquefaciens; rhizobacteria; PGPR
