First Report of Pomegranate Wilt Caused by Ceratocystis fimbriata in Sichuan Province

An expanded concept of Ceratocystis manginecans and five new species in the Latin American clade of Ceratocystis

The genus Ceratocystis contains a number of emerging plant pathogens, mostly members of the Latin American Clade (LAC), in which there are several unresolved taxonomic controversies. Among the most important are Brazilian pathogens in the C. fimbriata complex, C. manginecans and C. eucalypticola. Representatives of C. manginecans and C. eucalypticola from India and China, respectively, were shown to be fully interfertile in laboratory matings, and hybrids between the putative species were identified on Punica in India. An Indian tester strain was sexually compatible with representatives of what has been considered C. fimbriata on numerous hosts across Brazil. In this revision of the LAC, the name C. fimbriata is restricted to the widely dispersed Ipomoea strain, and C. manginecans is recognized as a Brazilian species that is important on Mangifera, Eucalyptus, and many other crops. C. mangivora and C. mangicola are also considered synonyms of C. manginecans. Based on phylogenetics and mating studies, two other Brazilian species are recognized: C. atlantica, sp. nov., and C. alfenasii, sp. nov., each with wide host ranges. Three new Caribbean species are recognized based on phylogenetics and earlier inoculation studies: C. costaricensis, sp. nov., on Coffea, C. cubensis, sp. nov., on Spathodea, and C. xanthosomatis, sp. nov., on the vegetatively propagated aroids Xanthosoma and Syngonium. Some of the other Ceratocystis species were based primarily on unique internal transcribed spacer (ITS) rDNA sequences, but the unreliability of rDNA sequences was demonstrated when intraspecific crossing of isolates with differing ITS sequences generated single-ascospore progeny with intragenomic variation in ITS sequences and others with new ITS sequences. Species recognition in Ceratocystis should use phenotype, including intersterility tests, to help identify which lineages are species. Although some species remain under-studied, we recognize 16 species in the LAC, all believed to be native to Latin America, the Caribbean region, or eastern USA.

Molecular Characterization and Genetic Variation in Ceratocystis fimbriata Ell. and Halst. on Pomegranate

Fifteen isolates of Ceratocystis fimbriata collected from different locations in Karnataka were characterized using ITS gene technology. It produced an amplification size of 600−650 bp, which indicated that all the isolates belong to the genus Ceratocystis, thus confirming the identity of the pathogenic isolates. To test genetic variability, isolates were analyzed using microsatellite markers. An UPGMA dendrogram for genetic variation among the isolates showed that all the isolates fell into two major clusters. The first cluster consisted of isolate Cf-10 and the second cluster was further divided into two sub-clusters. Sub-cluster one consisted of isolate Cf-2. Sub-cluster two was again divided into five groups. The first group included isolate Cf-13, the second group consisted of isolate Cf-14, the third group included isolates Cf-1, Cf-4, Cf-6, Cf-7, Cf-8 and Cf-9, the fourth group included Cf-5 and Cf-11, and the fifth group consisted of Cf-3, Cf-12 and Cf-15. The dissimilarity coefficient ranged from 0.00 to 0.20 among the isolates. Isolates Cf-1, Cf-3, Cf-4, Cf-5 Cf-6, Cf-7, Cf-8, Cf-9, Cf-11, Cf-12 and Cf-15 were found to be highly similar, as their dissimilarity coefficient was zero. Maximum dissimilarity (0.20) was found between isolate Cf-10 and all the other isolates, suggesting they were genetically distinct.

Genetic Bottlenecks for Two Populations of Ceratocystis fimbriata on Sweet Potato and Pomegranate in China

Chinese isolates of Ceratocystis fimbriata from sweet potato (Ipomoea batatas) and pomegranate (Punica granatum) were genetically compared with a worldwide collection of isolates from a variety of hosts. Isolates from black-rotted storage roots of sweet potato in China, Japan, Australasia, and the United States had identical internal transcribed spacer (ITS) ribosomal DNA (rDNA) sequences and only minor variation in microsatellite alleles. Sequences of their mating type genes were most similar to those of isolates from various hosts in Ecuador, a center of diversity for sweet potato. Isolates from Colocasia esculenta (taro) and pomegranate from Yunnan and Sichuan had only one ITS rDNA sequence (haplotype ITS5). This haplotype, sequences of mating type genes, and microsatellite alleles linked these isolates to isolates from Eucalyptus stumps in South China and diseased Eucalyptus trees in Brazil, supporting the hypothesis that the pomegranate population originated from Brazil via cuttings of Eucalyptus. Isolates from sweet potato and pomegranate in China were interfertile with tester strains of C. fimbriata, confirming that the causes of the two epidemics in China belong to a single biological species. However, other isolates from Eucalyptus stumps were intersterile with the tester strains and had ITS rDNA sequences typical of the Asian species, C. cercfabiensis.

New Ceratocystis species from Eucalyptus and Cunninghamia in South China

During routine surveys for possible fungal pathogens in the rapidly expanding plantations of Eucalyptus and Cunninghamia lanceolata in China, numerous isolates of unknown species in the genus Ceratocystis (Microascales) were obtained from tree wounds. In this study we identified the Ceratocystis isolates from Eucalyptus and Cunninghamia in the GuangDong, GuangXi, FuJian and HaiNan Provinces of South China based on morphology and through comparisons of DNA sequence data for the ITS, partial β-tubulin and TEF-1α gene regions. Morphological and DNA sequence comparisons revealed two previously unknown species residing in the Indo-Pacific Clade. These are described here as Ceratocystis cercfabiensis sp. nov. and Ceratocystis collisensis sp. nov. Isolates of Ceratocystis cercfabiensis showed intragenomic variation in their ITS sequences and four strains were selected for cloning of the ITS gene region. Twelve ITS haplotypes were obtained from 17 clones selected for sequencing, differing in up to seven base positions and representing two separate phylogenetic groups. This is the first evidence of multiple ITS types in isolates of Ceratocystis residing in the Indo-Pacific Clade. Caution should thus be exercised when using the ITS gene region as a barcoding marker for Ceratocystis species in this clade. This study also represents the first record of a species of Ceratocystis from Cunninghamia.

Genetic Analyses Trace the Yunnan, China Population of Ceratocystis fimbriata on Pomegranate and Taro to Populations on Eucalyptus in Brazil

Genotypes of the Latin American wilt pathogen Ceratocystis fimbriata have been moved around the world in vegetatively propagated material of various crop plants, including Ipomoea batatas (sweet potato), Colocasia esculenta (taro), and Eucalyptus spp. When compared to a worldwide collection of isolates of C. fimbriata, isolates from taro, Punica granatum (pomegranate), and Eriobotrya japonica (loquat) from Yunnan Province, China were found to have sequences of internal transcribed spacer (ITS) rDNA and mating type genes that were identical to isolates from Eucalyptus in Brazil. Analyses of 35 isolates with 14 microsatellite markers revealed that the Yunnan population was nearly uniform, consisting of only 19 alleles and seven closely related genotypes, suggesting that the population is not natural and is the result of an introduction. As in comparisons of sequences of ITS rDNA and mating type genes, the microsatellite alleles of the Yunnan isolates were most similar to those of Eucalyptus isolates from Minas Gerais and Bahia, Brazil, where C. fimbriata is native, soilborne, and commonly infects cuttings of Eucalyptus spp. used for rooting in nurseries. Thus, the Yunnan population, which is causing severe losses on pomegranate, may have been indirectly derived from introductions of C. fimbriata in contaminated Eucalyptus cuttings from Brazil.