Characterization of basal rot disease agent Fusarium oxysporum f.sp. cepae observed growing onions in Amasya and biological control by plant growth promoting rhizobacteria

Basal rot disease of onion, caused by Fusarium oxysporum f.sp. cepae (FOC), is an important soil-borne disease of onion worldwide. The causal organism infects the basal stem plate of the onion bulb and eventually kills the entire plant through degradation of the basal plate. This study was conducted for identifacition and biological control of onion basal rot disease agent FOC in different districts of Amasya province during 2015-2016 growing seasons. Isolates of FOC obtained from naturally infected onion plants in surveyed fields in Suluova, Merzifon, Gümüşhacıköy, Göynücek, Hamamözü, and Taşova disricts of Amasya province. All fungal isolates of FOC was identified by pathogenicity test and molechuler metod by using ITS1 and ITS4 primers. For biological control of disease, 269 putative phosphorus (P) solubilising plant growth promoting rhizobacterial (PGPR) isolates were obtained from rhizosphere of healty onion plants growing in surveyed fields in the region. These isolates were further tested to determine their suppressive antogonistic effects on the mycelial growth of FOC in dual culture tests in vitro conditions. Among the tested bacterial isolates, eight isolates were determined to inhibit mycelial growth of FOC at the highest rates of 72,6-75,3 % in dual culture tests. Among the all bacterial, twelve PGPR isolates, having the highest P-solubising potential and three the most effective antagonist isolates were selected to use in vivo pot experiments. The 15 bacterial isolates were identified as Enterobacter cloacae ssp. dissolvens (8), Yersinia intermedia (1), Pantoea agglomerans, Basillus subtilis (3) by using biochemical tests and BIOLOG profiling system. Two tested bacterial isolates were however not identified in species level.Seed treatment with selected isolates were found to suppress disease incidence in varying ratios of 9,9 - 77,8 % comparable to the only FOC experiments. In the absence of the pathogen, these isolates were also found to enhance plant growth parameter (such as lenght of onion leaf, number of onion leaf, root lenght of onion, head diameter onion, head onion dry and wet weight) in varying ratios in both pot and field experiments.