High species diversity in Colletotrichum associated with citrus diseases in Europe

Species of Colletotrichum are considered important plant pathogens, saprobes, and endophytes on a wide range of plant hosts. Several species are well-known on citrus, either as agents of pre- or post-harvest infections, such as anthracnose, postbloom fruit drop, tear stain and stem-end rot on fruit, or as wither-tip of twigs. In this study we explored the occurrence, diversity and pathogenicity of Colletotrichum spp. associated with Citrus and allied genera in European orchards, nurseries and gardens. Surveys were carried out during 2015 and 2016 in Greece, Italy, Malta, Portugal and Spain. A total of 174 Colletotrichum strains were isolated from symptomatic leaves, fruits, petals and twigs. A multi-locus phylogeny was established based on seven genomic loci (ITS, GAPDH, ACT, CAL, CHS-1, HIS3 and TUB2), and the morphological characters of the isolates determined. Preliminary pathogenicity tests were performed on orange fruits with representative isolates. Colletotrichum strains were identified as members of three major species complexes. Colletotrichum gloeosporioides s.str. and two novel species (C. helleniense and C. hystricis) were identified in the C. gloeosporioides species complex. Colletotrichum karstii, C. novae-zelandiae and two novel species (C. catinaense and C. limonicola) in the C. boninense species complex, and C. acutatum s.str. was also isolated as member of C. acutatum species complex. Colletotrichum gloeosporioides and C. karstii were the predominant species of Colletotrichum isolated. This study represents the first report of C. acutatum on citrus in Europe, and the first detection of C. novae-zelandiae from outside New Zealand. Pathogenicity tests revealed C. gloeosporioides s.str. to be the most virulent species on fruits. The present study improves our understanding of species associated with several disease symptoms on citrus fruits and plants, and provides useful information for effective disease management

Calonectria spp. causing leaf spot, crown and root rot of ornamental plants in Tunisia

Calonectria spp. are important pathogens of ornamental plants in nurseries, especially in the Northern Hemisphere. They are commonly associated with a wide range of disease symptoms of roots, leaves and shoots. During a recent survey in Tunisia, a number of Calonectria spp. were isolated from tissues of ornamental plants showing symptoms of leaf spot, crown and root rot. The aim of this study was to identify these Calonectria spp. using morphological and DNA sequence comparisons. Two previously undescribed Calonectria spp., C. pseudomexicana sp. nov. and C. tunisiana sp. nov., were recognised. Calonectria mexicana and C. polizzii are newly reported for the African continent. Pathogenicity tests with all four Calonectria spp. showed that they are able to cause disease on seedlings of Callistemon spp., Dodonaea viscosa, Metrosideros spp. and Myrtus communis

Phyllosticta citricarpa and sister species of global importance to Citrus.

Several Phyllosticta species are known as pathogens of Citrus spp., and are responsible for various disease symptoms including leaf and fruit spots. One of the most important species is P. citricarpa, which causes a foliar and fruit disease called citrus black spot. The Phyllosticta species occurring on citrus can most effectively be distinguished from P. citricarpa by means of multilocus DNA sequence data. Recent studies also demonstrated P. citricarpa to be heterothallic, and reported successful mating in the laboratory. Since the domestication of citrus, different clones of P. citricarpa have escaped Asia to other continents via trade routes, with obvious disease management consequences. This pathogen profile represents a comprehensive literature review of this pathogen and allied taxa associated with citrus, focusing on identification, distribution, genomics, epidemiology and disease management. This review also considers the knowledge emerging from seven genomes of Phyllosticta spp., demonstrating unknown aspects of these species, including their mating behaviour.TaxonomyPhyllosticta citricarpa (McAlpine) Aa, 1973. Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes, Order Botryosphaeriales, Family Phyllostictaceae, Genus Phyllosticta, Species citricarpa.Host rangeConfirmed on more than 12 Citrus species, Phyllosticta citricarpa has only been found on plant species in the Rutaceae.Disease symptomsP. citricarpa causes diverse symptoms such as hard spot, virulent spot, false melanose and freckle spot on fruit, and necrotic lesions on leaves and twigs.Useful websitesDOE Joint Genome Institute MycoCosm portals for the Phyllosticta capitalensis (https://genome.jgi.doe.gov/Phycap1), P. citriasiana (https://genome.jgi.doe.gov/Phycit1), P. citribraziliensis (https://genome.jgi.doe.gov/Phcit1), P. citrichinaensis (https://genome.jgi.doe.gov/Phcitr1), P. citricarpa (https://genome.jgi.doe.gov/Phycitr1, https://genome.jgi.doe.gov/Phycpc1), P. paracitricarpa (https://genome.jgi.doe.gov/Phy27169) genomes. All available Phyllosticta genomes on MycoCosm can be viewed at https://genome.jgi.doe.gov/Phyllosticta

AzeR, a transcriptional regulator that responds to azelaic acid in Pseudomonas nitroreducens

This is the final version. Available on open access from the Microbiology Society via the DOI in this recordAzelaic acid is a dicarboxylic acid that has recently been shown to play a role in plant-bacteria signalling and also occurs naturally in several cereals. Several bacteria have been reported to be able to utilize azelaic acid as a unique source of carbon and energy, including Pseudomonas nitroreducens. In this study, we utilize P. nitroreducens as a model organism to study bacterial degradation of and response to azelaic acid. We report genetic evidence of azelaic acid degradation and the identification of a transcriptional regulator that responds to azelaic acid in P. nitroreducens DSM 9128. Three mutants possessing transposons in genes of an acyl-CoA ligase, an acyl-CoA dehydrogenase and an isocitrate lyase display a deficient ability in growing in azelaic acid. Studies on transcriptional regulation of these genes resulted in the identification of an IclR family repressor that we designated as AzeR, which specifically responds to azelaic acid. A bioinformatics survey reveals that AzeR is confined to a few proteobacterial genera that are likely to be able to degrade and utilize azelaic acid as the sole source of carbon and energy