Archivio Journal of Plant Pathology

Abstract:

A protocol based on API 20E; REP-PCR or Biolog analyses is described for rapid and reliable identification of Brenneria nigrifluens among the bacteria isolated from bark cankers in walnut plants. Bacteria that are soluble in 3% KOH solution (Gram negative); oxidase negative and with oxidative (O) and fermentative (F) metabolism are subjected to API 20E; REP-PCR or Biolog analyses. Isolates that generate a 7-digit code = 0005773 in the API 20E system; a REP-PCR fingerprint or Biolog profile very similar (87-100%) to those of the B. nigrifluens reference strains are assigned to this bacterial species. Using the protocol; we identified 4 isolates of B. nigrifluens among the 28 gram negative isolates (14 with O/F and 14 with O metabolism) obtained from bark cankers in walnut plantations on 10 farms in Central Italy. Among the other ten O/F isolates; only 2; assigned to Pectobacterium chrysanthemi; were identified with reliability by Biolog analysis. This analysis also permits identification of isolates with O metabolism. A pathogenicity test performed on walnut plants revealed that only the 4 B. nigrifluens isolates provoked bark canker symptoms 3 months after the inoculation. We also found that one isolate of four and the type strain (LMG 2694T) of B. nigrifluens are urease negative; when determined in Dye’s medium. Since our data are in contrast with those previously reported; this phenotypic character needs further verification for B. nigrifluens identification.