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 × 10 6-7.1 × 10 7 CFU/g 1 day after seed bacterization. The population of the two EB isolates in cucumber tissues were found to be about 2 × 10 4-7.5 × 10 4 CFU/g in roots and 3.8 × 10 4-2.2 × 10 5 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.
Background
Bacterial canker and subsequent gummosis are caused by multiple pathogens and lead to significant yield and productivity losses in sweet cherry cultivation in Turkey. This study identified that Pseudomonas syringae pathovars were responsible for bacterial canker on sweet cherry orchards by using classical and molecular methods and evaluated the biocontrol effects of bacteriophages against P. syringae pv. syringae.
Results
Pathogenic bacteria were isolated from samples taken from plants showing symptoms of bacterial canker in cherry orchards located in İzmir and Manisa provinces. Specific pathogens were identified using pathogenicity, phenotypic tests, and simplex PCR. Bacteriophages effective against P. syringae strains were isolated from soil contaminated with pathogens identified in the diseased orchards using an optimized isolation protocol. The biocontrol activity of bacteriophage isolates against P. syringae pv. syringae was tested in vitro and in vivo. The results of pathogenicity tests on immature sweet cherry fruits and micropropagated cherry plantlets revealed 10 pathogenic bacteria isolates from 44 plant samples taken from sweet cherry orchards showing symptoms of bacterial canker.
Conclusions
Ten isolates were identified as Pseudomonas syringae pv. syringae. Nine different pure bacteriophage isolates were effective. The results indicated that bacteriophage isolates may demonstrate variable reactivity against P. syringae pathovars.
Turkey, with an apricot (Prunus armeniaca L.) production amount of 833,398 tons per year, ranks first in fresh apricot production and dried apricot export in the world. Malatya, Iğdır, and Elazığ with amounts of apricot production constitute the main apricot production centers in Turkey. Many table and dried apricot cultivars have been grown in Turkey. Economically important apricot cultivars such as cv.Şalak (or Aprikoz), cv.Tebereze, cv.Ordubat, cv.Ağcanabat, and cv.Ağerik are widely grown in the Aras Valley, including Iğdır and Kağızman. In this study, DNA barcoding of local cultivars based on the ITS region was performed and their distribution was shown in the Aras Valley. The reactions of these apricot cultivars to the causal agents of bacterial canker, which negatively affect the yield and quality of apricot cultivation, were also determined. Alternative methods such as image-processing technology and CHAID analysis have also been successfully used for cultivar reaction tests. It was determined that "cv.Şalak" is the most common apricot cultivar in the Aras Valley. In addition, the Ağcanabat cultivar was sensitive to the causal agents of disease, and other local apricot cultivars were tolerant to it.
Bacterial canker of stone fruits caused by Pseudomonas syringae pv. syringae (Pss) and Pseudomonas syringae pv. morsprunorum (Psm race‐1/Psm race‐2) may lead to significant yield and crop losses in apricot (Prunus armeniaca L.) cultivation areas in Türkiye. Strains pathogenic to apricot were isolated from trees with symptoms (mainly necrotized buds and dieback) of bacterial canker in orchards in Aras Basin. Pathogens were characterized using pathogenicity tests, phenotypic assays, end‐point PCR and multilocus sequence analysis (MLSA). Fifteen Pseudomonas syringae strains were isolated from 205 plant samples collected from apricot orchards showing symptoms of bacterial canker. As a consequence of the diagnostic tests, all isolates were identified as P. syringae pv. syringae. In this study, Pss, Psm R1 and Psm R2 strains in stone fruits were separated into different phylogroups (Pg‐2, Pg‐3, sPg‐1b) based on MLSA. Turkish strains obtained from stone fruits, particularly apricot, showed genetic heterogeneity, and clustered in different sub‐phylogroups (sPg‐2b, sPg‐2c, sPg‐2d). All these strains except strain K258 are also clustered in the same sub‐phylogroups (sPg‐2b and sPg‐2d) with other strains from different countries especially Iran, Lebanon, etc. Strain K258 isolated from apricot was clustered in sPg‐2c with Pss strain 642 (USA). The risk of bacterial canker disease in apricot growing areas is considered using GIS in this study. It was determined that a significant part of the Iğdır Plain, the biggest agricultural area in the Aras Basin, is at very high risk.
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