Abstract
Endophytic bacteria (EB) isolated from healthy cucumber plant tissues (e.g., root, stem, leaves) were evaluated as possible biological control of Pseudomonas syringae pv. lachrymans, the causative agent of angular leaf spot disease in cucumber. In this study, 24 endophytic bacteria were selected for tests based on biocontrol traits such as indole-3-acetic acid and siderophore production, solubilization of phosphate, and inhibition growth of P. syringae pv. lachrymans in vitro. Some of the selected endophytes successfully inhibited the pathogen were tested in pots. In the pot experiment, two isolates (CB361-80) and (CC372-83) were selected as the most promising biocontrol agents tested against the pathogen. According to the identification carried out by using 16S rRNA primers and sequence analysis, the two selected endophyte isolates (CB361-80) and (CC372-83) showed 99% similarity to Ochrobactrum pseudintermedium and Pantoea agglomerans, respectively. Two EB isolates colonized seeds at the rate of 3 × 106–7.1 × 107 CFU/g 1 day after seed bacterization. The population of the two EB isolates in cucumber tissues were found to be about 2 × 104–7.5 × 104 CFU/g in roots and 3.8 × 104–2.2 × 105 CFU/g in shoots 45 days after seed bacterization. The populations of the two isolates in the root and shoot tissues did not decrease following the inoculation of the pathogenic bacterium. The endophytic strains CB361-80 (Ochrobactrum sp.) and CC372-83 (Pantoea sp.) successfully colonized the cucumber tissues.
Highlights
Cucumber (Cucumis sativus L.) is one of the most widely cultivated vegetable crops worldwide
In vivo biocontrol effects of endophytic bacterial isolates against Pseudomonas syringae pv. lachrymans According to the average of duplicate experiments under the growth chamber conditions (Table 3), 14 days after pathogen inoculation, approximately 12.5% of the Endophytic bacteria (EB) isolates tested (CA332-73, CB361-80, CC372-83) reduced Psl disease severity by > 50% with respect to that of plants inoculated with pathogen only
Statistical analyses of the two experiments indicated that EB isolates CA332-73, CB361-80, and CC372-83 were the ones to Pseudomonas syringae pv. lachrymans disease severity in cucumber plants under growth chamber conditions
Summary
Cucumber (Cucumis sativus L.) is one of the most widely cultivated vegetable crops worldwide. Lachrymans (Smith & Bryan) Young, Dye & Wilkie (Psl), which is the causative agent of angular leaf spot disease (Smith and Bryan 1915). It may cause significant yield losses in both greenhouse and field production (Bhat et al 2007). Under climatic conditions conducive to its proliferation, the disease caused severe damage and economic loss to farmers of cucumber and other cucurbits in Turkey (Ozaktan and Bora 1994). This disease resulted in the loss of cucumber production at the state of Wisconsin (USA).
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