First Report of Bacterial Canker Caused by Pseudomonas syringae pv. morsprunorum Race 1 on Peach from Khyber Pakhtunkhwa Province of Pakistan

Peach (Prunus persica L.) fruit, which is rich in minerals, fiber, and vitamins, is a major fruit in Khyber Pakhtunkhwa (KPK) and northern areas of Pakistan. With an average production of 30,000 metric tons, it is cultivated on an area of 56,000 ha in KPK. During a survey of 29 peach orchards in the two consecutive growing seasons from 2014 to 2016, leaves and fruits with water-soaked brown necrotic lesions and stems with canker and gum execution were observed. Mean disease incidence was recorded as 49% on a cultivar locally known as 6 1/2. A total of 260 samples were collected in December and January (blooming stage) to May (fruiting stage). After isolation on nutrient agar medium, the formed bacterial colonies were streaked on King’s B medium to detect florescence under ultraviolet light. Cycloheximide at 50 mg/liter was added to the medium to prevent fungal growth. According to the LOPAT scheme, a total of 32 recovered isolates were gram negative; levan and tobacco hypersensitivity positive; and oxidase, potato soft rot, and arginine dihydrolase negative and were confirmed as Pseudomonas syringae. According to the GAATa scheme, gelatin and aesculin hydrolysis were negative, whereas tyrosinase and tartrate were positive, which confirmed 11 isolates were pathovar morsprunorum race 1 (Lelliott and Stead 1987). Further identification of P. syringae pv. morsprunorum race 1 was confirmed by polymerase chain reaction amplification of 16S rRNA and gyrB gene (Karlson et al. 1993; Yamamoto et al. 2000). Obtained sequences of 16S rRNA and gyrB gene (GenBank accession nos. KY364875 and MF401398, respectively) showed 96 to 99% genetic similarity with already reported P. syringae pv. morsprunorum race 1 sequences (GenBank accession nos. KF019104 and HG000214, respectively). Pathogenicity was tested by inoculating fresh peach fruits with bacterial suspension (10⁸ CFU/ml) of these two strains together with a pathotype strain incubated at 27 ± 2°C. A set of healthy fruits inoculated with double-distilled water was used as a control (Kaluzna et al. 2012). Five to seven days after inoculation, water-soaked, brown lesions with yellow margins were observed on the fruits inoculated with bacterial strains. The pathogen was reisolated and confirmed P. syringae pv. morsprunorum race 1 using LOPAT and GATTa tests. To our knowledge, this is the first report of P. syringae pv. morsprunorum race 1 from KPK province of Pakistan, and the information will help in devising quarantine measures to limit the pathogen prevalence.