A new pathovar of Pseudomonas amygdali as causal agent ofbacterial leaf spot and die-back of hazelnut

Background and Aim : Hazelnut (Corylus avellanae), a plant native to the temperate northernhemisphere, is cultivated in Iran mainly in the northern parts of the country. Irregular reddishbrownnecrotic spots on hazelnut leaves and fruit bracts were observed during ۲۰۱۸ and ۲۰۱۹ inhazelnut orchards of the Guilan province. The objective of the present study was identification ofthe causative agent of hazelnut leaf and bract spot.Methods : Samples of hazelnut leaves and fruits showing necrotic lesions were collected fromorchards in several locations of Guilan province, northern Iran, in the growing seasons of ۲۰۱۸and ۲۰۱۹. Pathogenicity assays were performed on two years old hazelnut trees cv. Alamut. Allstrains were subjected to phenotypic assays including LOPAT and GATTa tests. The housekeepinggenes gyrB, rpoB, rpoD, gapA, and gltA of four pathogenic strains were partially amplified,sequenced and Phylogenetic trees were constructed.Results : Symptoms observed on the affected hazelnut trees consisted of water-soaked, smallangular lesions, which subsequently turned into reddish-brown necrotic areas. When the lesionsexpanded, they coalesced and necrotic blotches were formed leading to wilting of leaves anddefoliation. Dieback of the defoliated branches followed. Isolation from symptomatic tissuesyielded bacterial colonies, which were selected for characterization. Thirty-five strains proved tobe pathogenic on hazelnut. All strains were Gram negative, produced a fluorescent pigment onKing’s medium B and a hypersensitive reaction on tobacco. Thirty-five strains belong to LOPATgroup Ia (+ ̵ ̵ ̵ ̵ +) and positive for gelatin liquefaction and aesculin hydrolysis but negative fortyrosinase activity and tartrate utilization (G+A+T-Ta-). Phylogenetic analyses based on partialsequences of the five protein-encoding housekeeping genes indicated that the representative strainswere identical to each other and formed a branch in the phylogram among other pathovars ofPseudomonas amygdali.Conclusion : Based on phenotypic and pathogenicity characteristics and phylogenetic affiliation,the bacterium inciting a not earlier described hazelnut disease, appears to be a novel pathovar ofP. amygdali, for which here provisionally is named P. amygdali pv. corylicola.

کلیدواژه ها:

Corylus avellanae ، Bract Spot ، Multilocus Sequence Analysis ، Iran