Didem Canik Orel

Fusarium crown and root rot, caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL), is a Fusarium crown and root rot, caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL), is a destructive soil-borne disease of tomato and other solanaceous crops. This two-year study evaluated whether seed microbiome modification via flowering-stage inoculation with endophytic bacteria could protect tomato and eggplant seedlings against FORL, compared with conventional direct seed coating. Seeds from parent plants inoculated at flowering with Pseudomonas fluorescens L5b or Pseudomonas gessardii L13 (L5-B, L13) were compared with directly coated seeds (K-L5-B, KL-13). Seedlings were challenged with FORL and assessed six weeks later. In eggplant, K-L5-B achieved the greatest disease reduction in both years (19.44% and 24.56%), while L13 failed to suppress disease in year one. In tomato, K-L5-B reduced disease severity from 64.88% (positive control) to 46.40% (28.48% reduction), followed by KL-13 (24.49%), L13 (20.83%), and L5-B (18.02%). Bacterial treatments partially mitigated FORL-induced growth impairment, especially for chlorophyll content and shoot fresh weight. In eggplant, KL-13 increased shoot fresh weight to 27.15 g, exceeding the positive control (22.13 g) and approaching the healthy control (26.19 g). Principal component analysis explained 84.3% of growth variation, with biomass traits driving treatment separation. Overall, flowering-stage inoculation produced seeds with biologically meaningful protective capacity, but direct bacterial seed coating provided more consistent protection under severe FORL pressure.

Erwinia persicina, the causal agent of lettuce soft rot, has recently emerged as an important bacterial pathogen, and information on its biological control remains limited. In this study, the biocontrol potential of endophytic Pseudomonas and Bacillus species isolated from lettuce was evaluated as an alternative disease management strategy. Thirty endophytic bacterial isolates were screened in vitro for antagonistic activity against E. persicina isolate Ep_Tr2, and six isolates showing inhibition zone were selected for further characterization. The selected strains, including Bacillus mojavensis Bmj1, Bacillus amyloliquefaciens Ba7, and Pseudomonas putida Lt68, were assessed for plant growth-promoting traits, including indole-3-acetic acid production, ammonia production, and proteolytic activity. Among these isolates, Lt68 was among the highest ammonia-producing strains and showed intermediate indole-3-acetic acid production, whereas proteolytic activity was detected in all selected isolates without significant differences among them. Promising strains were evaluated in vivo under greenhouse conditions using foliar and root applications performed 24–72 h before or simultaneously with pathogen inoculation. Disease severity was assessed 14 days after inoculation using a 0–4 symptom scale and analysed by two-way ANOVA. Foliar application of Bacillus mojavensis Bmj1 and Pseudomonas putida Lt68 24 h prior to pathogen inoculation significantly reduced symptom development, while Bacillus amyloliquefaciens Ba7 showed delayed efficacy at 48 and 72 h. Root applications did not result in significant disease suppression. These findings demonstrate the potential of endophytic bacteria for the biological control of Erwinia persicina in lettuce and highlight the importance of application timing and method for effective disease management.

Optical density at 600 nm (OD600) is widely used to estimate bacterial cell density, yet the conversion of OD600 values to viable cell counts (CFU.mL⁻¹) is often based on generic factors that ignore strain-level variability. This practice can introduce substantial quantitative error, particularly in plant–microbe interaction studies where precise inoculum standardization is essential. In this study, we investigated the strain-specific relationship between OD600 and CFU.mL⁻¹ in five environmental isolates of Pseudomonas fluorescens using an AI-assisted colony counting approach. Serial dilutions covering a wide OD600 range were plated and enumerated using a semi-automated image analysis pipeline with manual verification. For each isolate, calibration curves were constructed by relating OD600 to log10-transformed CFU.mL⁻¹ values. Model fitting showed that a logarithmic function provided the best description of the OD–CFU relationship across the tested range (R² = 0.88–0.97). When OD600 values corresponding to the 0.5 McFarland standard (0.08) were applied to isolate-specific models, predicted viable counts varied by up to ~4.2-fold among isolates. One-way ANOVA confirmed a highly significant isolate effect on CFU estimates. These findings demonstrate that OD600–CFU relationships are not conserved even within a single bacterial species and that reliance on generic conversion factors can lead to substantial over- or underestimation of viable cell numbers. The AI-assisted workflow enabled the generation of dense, statistically robust calibration datasets that would be impractical with manual counting alone. We conclude that isolate- and instrument-specific OD–CFU calibration should be considered a methodological requirement for quantitative microbiology, particularly in plant science, biocontrol, and microbial ecology studies.

This study aimed to unveil the genetic diversity among 47 bacterial isolates from various species using start codon targeted (SCoT) markers. Six SCoT primers yielded 219 reproducible bands, with 89.04% exhibiting polymorphism. The amplification process generated 28 to 50 fragments per primer, with an average of 36.50. Genetic diversity was quantified using polymorphic information content (PIC) values ranging from 0.11 to 0.14, with SCoT32 showing the highest PIC (0.14) and SCoT23 the lowest (0.11). The resolving power (RP) index, used to assess primer discriminatory power, varied significantly, with SCoT23 demonstrating the highest RP (6.00) and SCoT29 the lowest (4.51). Comparative analysis with conventional markers like M13 and (GTG)₅ revealed that certain SCoT primers exhibited superior PIC values, which indicates enhanced utility for interspecies differentiation. The high discrimination level achieved by SCoT primers underscores their effectiveness in genetic differentiation and biodiversity assessment within bacterial populations. This research highlights SCoT markers as powerful tools for microbial genetic studies, which offers valuable insights into bacterial diversity and provides a robust methodological framework for future investigations aimed at elucidating genetic variation and improving species identification. The application of SCoT markers represents a significant advancement in molecular techniques for bacterial characterization and phylogenetic analysis, demonstrating their potential to enhance our understanding of microbial genetics and evolution.

Fruit maturity for seed production can occur at various times because of the continual flowering of pepper plants. Accordingly, seeds with different maturity are acquired as the fruits are collected in a single harvest. Immature seeds obtained in this harvest may lead to a decrease in the quality of seed lots. Therefore, this research aimed to evaluate the influence of four different endophytic bacteria strains (Pseudomonas fluorescens strain L5b, Pseudomonas gessardii strain L13, Bacillus subtilis strain Bs1 and Bacillus mojavensis strain ApBm) on germination and seedling vigor of immature and mature bell pepper seeds. To obtain seeds with different maturity levels, fruits were collected 45–49 days after flowering for immature seeds and 65–69 days for mature seeds. The effectiveness of these bacteria strains was examined by coating seeds with four different endophytic bacteria strains separately. Additionally, to see the activity of endophytic bacteria more clearly, a mock treatment with sterile water was added to the experiment as a control (+) group. Bio-priming (especially strain Bs1 and L13) improved germination and seedling emergence characteristics of both immature and mature seed lots compared to control groups (p < 0.05). The results demonstrate that bio-priming with beneficial endophytic bacteria can be used to stimulate the quality of both immature and mature seeds from the pepper.

Pseudomonas viridiflava (Burkholder 1930) Dowson 1939 is a multihost plant pathogenic bacterium all over the world and also in Turkey. The aim of this study was to identify the pathogenic bacteria causing the symptoms of water-soaked necrotic leaf spots, dark brown spots on leaves, tip burn of leaf in curly type lettuce (Lactuca sativa var. crispy) grown in the field conditions in Beypazarı region and to reveal the reactions of some lettuce cultivars against the bacteria. For this purpose, twelve isolates were obtained from 4 different locations. Pathogenicity tests were conducted on curly type lettuce and all isolates were found pathogenic on the host. Isolated bacteria were evaluated for Gram reaction, LOPAT tests, colony morphology on King’s Medium B and carbon sources utilization by VITEK-2 system and identified as Pseudomonas viridiflava. The 16S rDNA region of a selected isolate representing the similar isolates in all tests was sequenced for genetic confirmation and the obtained sequence was submitted to the GeneBank under the accession number MN_539659. The result of the obtained sequence was 99.75% similar to the respective reference sequence after BLAST analysis. Reaction of the three different widely produced lettuce types, iceberg, curly and romaine types, with ten varieties against the causative bacterial agent was evaluated and the difference between the varieties found significant statistically. In this study, P. viridiflava was detected in lettuce in Central Anatolia for the first time.

ISHS IX International Congress on Hazelnut Molecular characterization and sequence detection of Apple mosaic virus hazelnut isolates