Evidence for the presence of a bacterial endosymbiont in the pecan scab pathogen Venturia effusa (basyonym: Fusicladium effusum).

AIMS: To determine whether Venturia effusa, the causative fungal agent of pecan scab, harbours a bacterial symbiont.

METHODS AND RESULTS: Venturia effusa isolates were maintained on potato dextrose agar amended with antibiotics (chloramphenicol (100 μg ml-1 ) and tetracycline 100 (μg ml-1 )). Genomic DNA extracted from mycelia was used to target eubacterial 16S rDNA. A 1·4-kbp PCR amplified product using 16S rDNA degenerate primers was cloned, sequenced and found to have 99% identities with Actinobacteria representatives. Attempts to culture the detected bacteria apart from the fungus following agitation and fungal cell lysis were unsuccessful using standard bacteriological media under either aerobic or anaerobic conditions. Fungal structures were visualized using scanning electron microscopy and putative bacterial formations associated with the fungal mycelia were observed. Fluorescence in situ hybridization using 16S rDNA oligonucleotides illuminated spores and portions of the hyphae.

CONCLUSIONS: This is the first report to provide both molecular microbiological and microscopic evidence in support of the hypothesis that V. effusa harbours endosymbiotic bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY: Findings from this research contribute fundamental information regarding the biology of the fungus that may ultimately lead to identifying a target of the pathogen for use in management and/or avoidance strategies.