Pseudomonas syringae causing bacterial canker on apple trees in Brazil

ABSTRACT In March 2016, wilt and shoot blight were observed on five-year-old apple trees (Malus domestica) cultivar Maxi Gala in a commercial orchard in São Joaquim city, state of Santa Catarina, Brazil. Isolation on culture media, biolog, biochemical, LOPAT tests, and whole genome sequencing were performed. Koch’s postulates were fulfilled on apple stems, leaves and fruits. The taxonomic position of a representative strain was determined by in silicoDNA-DNA hybridization using the Genome-to-Genome Distance Calculator which showed 93.9% similarity with Pseudomonas syringae. Results of biolog and biochemical tests did not match those expected for pv. papulans, morsprunorum or syringae. To our knowledge this is the first report of P. syringae causing bacterial canker in commercial apple orchards in Brazil.摘要：2016年3月，巴西圣卡塔琳娜州圣若阿金城的一处商业苹果园内，研究人员在5年生苹果（Malus domestica）‘马克西·嘎拉’（Maxi Gala）品种植株上发现了萎蔫病与枝枯病症状。研究人员开展了培养基分离培养、Biolog鉴定试验（Biolog）、生化试验及LOPAT试验（LOPAT tests），并完成了全基因组测序。通过科赫氏法则（Koch’s postulates）验证，该病原菌可成功侵染苹果的茎、叶及果实。利用基因组-基因组距离计算器（Genome-to-Genome Distance Calculator）进行计算机模拟DNA-DNA杂交，明确了代表性菌株的分类地位，结果显示其与丁香假单胞菌（Pseudomonas syringae）的相似性达93.9%。Biolog鉴定与生化试验的结果，与丁香假单胞菌致变型papulans、morsprunorum及syringae的预期检测结果均不相符。据目前所知，这是巴西商业苹果园中首次报道由丁香假单胞菌引发细菌性溃疡病。