Table_1_Xanthomonas citri pv. viticola Affecting Grapevine in Brazil: Emergence of a Successful Monomorphic Pathogen.pdf

The pathovar viticola of Xanthomonas citri causes bacterial canker of grapevine. This disease was first recorded in India in 1972, and later in Brazil in 1998, where its distribution is currently restricted to the northeastern region. A multilocus sequence analysis (MLSA) based on seven housekeeping genes and a multilocus variable number of tandem repeat analysis (MLVA) with eight loci were performed in order to assess the genetic relatedness among strains from India and Brazil. Strains isolated in India from three related pathovars affecting Vitaceae species and pathogenic strains isolated from Amaranthus sp. found in bacterial canker-infected vineyards in Brazil were also included. MLSA revealed lack of diversity in all seven genes and grouped grapevine and Amaranthus strains in a monophyletic group in X. citri. The VNTR (variable number of tandem repeat) typing scheme conducted on 107 strains detected 101 haplotypes. The total number of alleles per locus ranged from 5 to 12. A minimum spanning tree (MST) showed that Brazilian strains were clearly separated from Indian strains, which showed unique alleles at three loci. The two strains isolated from symptomatic Amaranthus sp. presented unique alleles at two loci. STRUCTURE analyses revealed three groups congruent with MST and a fourth group with strains from India and Brazil. Admixture among populations were observed in all groups. MST, STRUCTURE and e-BURST analyses showed that the strains collected in 1998 belong to two distinct groups, with predicted founder genotypes from two different vineyards in the same region. This suggest that one introduction of grape planting materials contaminated with genetically distinct strains took place, which was followed by pathogen adaptation. Genome sequencing of one Brazilian strain confirmed typical attributes of pathogenic xanthomonads and allowed the design of a complementary VNTR typing scheme dedicated to X. citri pv. viticola that will allow further epidemiological survey of this genetically monomorphic pathovar.

柑橘黄单胞菌（Xanthomonas citri）葡萄致病变种（pv. viticola）可引起葡萄细菌性溃疡病。该病害于1972年首次在印度被报道，随后于1998年在巴西被发现，目前其在巴西的分布仅局限于东北部地区。本研究基于7个持家基因开展多位点序列分析（multilocus sequence analysis, MLSA），并结合8个基因座的多位点可变数目串联重复序列分析（multilocus variable number of tandem repeat analysis, MLVA），以评估印度与巴西菌株间的遗传亲缘关系。本研究还纳入了印度地区分离自3种侵染葡萄科（Vitaceae）物种的相关致病变种菌株，以及从巴西细菌性溃疡病染病葡萄园中的苋属（Amaranthus sp.）植株上分离得到的致病菌株。MLSA分析结果显示，7个基因均未检测到遗传多样性，且将葡萄菌株与苋属菌株聚类为柑橘黄单胞菌的一个单系类群。对107株菌株开展可变数目串联重复序列（variable number of tandem repeat, VNTR）分型分析，共检测到101个单倍型；每个基因座的等位基因数量介于5至12之间。最小生成树（minimum spanning tree, MST）分析结果显示，巴西菌株与印度菌株明显分化，印度菌株在3个基因座上带有独特等位基因；从染病苋属植株上分离得到的2株菌株，在2个基因座上带有独特等位基因。STRUCTURE群体结构分析显示，存在3个与MST分析结果一致的类群，以及1个同时包含印度与巴西菌株的类群；所有类群中均检测到种群间的基因交流现象。MST、STRUCTURE以及eBURST分析结果显示，1998年采集的菌株可分为2个不同类群，其推测的奠基者基因型分别来自同一区域内的2个不同葡萄园。这表明，携带遗传差异菌株的葡萄种植材料曾发生一次传入事件，随后病原菌发生了适应性演化。对1株巴西菌株进行全基因组测序，验证了致病黄单胞菌的典型特征，并据此设计了针对柑橘黄单胞菌葡萄致病变种（X. citri pv. viticola）的互补型VNTR分型方案，可用于该遗传单态性致病变种的后续流行病学调查。