A Survey on Occurrence of Cladosporium fulvum Identifies Race 0 and Race 2 in Tomato-Growing Areas of Argentina

Beyond the genomes of Fulvia fulva (syn. Cladosporium fulvum) and Dothistroma septosporum: New insights into how these fungal pathogens interact with their host plants

Fulvia fulva and Dothistroma septosporum are closely related apoplastic pathogens with similar lifestyles but different hosts: F. fulva is a pathogen of tomato, whilst D. septosporum is a pathogen of pine trees. In 2012, the first genome sequences of these pathogens were published, with F. fulva and D. septosporum having highly fragmented and near-complete assemblies, respectively. Since then, significant advances have been made in unravelling their genome architectures. For instance, the genome of F. fulva has now been assembled into 14 chromosomes, 13 of which have synteny with the 14 chromosomes of D. septosporum, suggesting these pathogens are even more closely related than originally thought. Considerable advances have also been made in the identification and functional characterization of virulence factors (e.g., effector proteins and secondary metabolites) from these pathogens, thereby providing new insights into how they promote host colonization or activate plant defence responses. For example, it has now been established that effector proteins from both F. fulva and D. septosporum interact with cell-surface immune receptors and co-receptors to activate the plant immune system. Progress has also been made in understanding how F. fulva and D. septosporum have evolved with their host plants, whilst intensive research into pandemics of Dothistroma needle blight in the Northern Hemisphere has shed light on the origins, migration, and genetic diversity of the global D. septosporum population. In this review, we specifically summarize advances made in our understanding of the F. fulva-tomato and D. septosporum-pine pathosystems over the last 10 years.

The Diversity of Passalora fulva Isolates Collected from Tomato Plants in U.S. High Tunnels

High tunnels extend the growing season of high value crops, including tomatoes, but the environmental conditions within high tunnels favor the spread of the tomato leaf mold pathogen, Passalora fulva (syn. Cladosporium fulvum). Tomato leaf mold results in defoliation, and if severe, losses in yield. Despite substantial research, little is known regarding the genetic structure and diversity of populations of P. fulva associated with high tunnel tomato production in the United States. From 2016 to 2019, a total of 50 P. fulva isolates were collected from tomato leaf samples in high tunnels in the Northeast and Minnesota. Other Cladosporium species were also isolated from the leaf surfaces. Koch's postulates were conducted to confirm that P. fulva was the cause of the disease symptoms observed. Race determination experiments revealed that the isolates belonged to either race 0 (six isolates) or race 2 (44 isolates). Polymorphisms were identified within four previously characterized effector genes: Avr2, Avr4, Avr4e, and Avr9. The largest number of polymorphisms were observed for Avr2. Both mating type genes, MAT1-1-1 and MAT1-2-1, were present in the isolate collection. For further insights into the pathogen diversity, the 50 isolates were genotyped at 7,514 single-nucleotide polymorphism loci using genotyping-by-sequencing. Differentiation by region but not by year was observed. Within the collection of 50 isolates, there were 18 distinct genotypes. Information regarding P. fulva population diversity will enable better management recommendations for growers, as high tunnel production of tomatoes expands.

Novel Botrytis and Cladosporium Species Associated with Flower Diseases of Macadamia in Australia

Macadamia (Macadamia integrifolia) is endemic to eastern Australia and produces an edible nut that is widely cultivated in commercial orchards globally. A survey of fungi associated with the grey and green mold symptoms of macadamia flowers found mostly species of Botrytis (Sclerotiniaceae, Leotiomycetes) and Cladosporium (Cladosporiaceae, Dothideomycetes). These isolates included B. cinerea, C. cladosporioides, and unidentified isolates. Amongst the unidentified isolates, one novel species of Botrytis and three novel species of Cladosporium were delimited and characterized by molecular phylogenetic analyses. The new species are Botrytis macadamiae, Cladosporium devikae, C. macadamiae, and C. proteacearum.

Endomycobiome associated with females of the planthopper Delphacodes kuscheli (Hemiptera: Delphacidae): A metabarcoding approach

A metabarcoding approach was performed aimed at identifying fungi associated with Delphacodes kuscheli (Hemiptera: Delphacidae), the main vector of “Mal de Río Cuarto” disease in Argentina. A total of 91 fungal genera were found, and among them, 24 were previously identified for Delphacidae. The detection of fungi that are frequently associated with the phylloplane or are endophytes, as well as their presence in digestive tracts of other insects, suggest that feeding might be an important mechanism of their horizontal transfer in planthoppers. This study draws the baseline for future research regarding mutualistic associations present in D. kuscheli as well as their physiological role in the life cycle of this important pest that might lead to developing new management strategies to keep insects populations under control.

Identification of an intermediate for 1,8-dihydroxynaphthalene-melanin synthesis in a race-2 isolate of Fulvia fulva (syn. Cladosporium fulvum)

Fulvia fulva (syn. Cladosporium fulvum, Mycosphaerellaceae) is a dematiaceous fungus that causes tomato leaf mould. It is characterized by its biotrophic lifestyle and the synthesis of the bianthraquinone secondary metabolite, cladofulvin. The aim of the study was to characterize the dark pigment photochemically synthesized by F. fulva and to elucidate its biochemical pathway. We isolated a black pigment from in vitro cultures of the fungus. We determined the pigment to be 1,8-dihydroxynaphthalene (DHN)-melanin based on its chemical and photochemical characteristics, as well as the presence of flaviolin, when fungal reductases were inhibited by tricyclazole. Furthermore, the pks1 gene involved in pigment synthesis has a KS domain already associated with DHN-melanin. Our findings support the relevance of studying melanization in F. fulva.

Microbial Endophytes that Live within the Seeds of Two Tomato Hybrids Cultivated in Argentina

Tomato (Solanum lycopersicum L.) is probably the most important vegetable consumed around the world, and like other produce is affected by stresses and diseases that reduce the yield and production. The purpose of this work was to study the phytobiome of the tomato seeds of two hybrids in order to understand first of all whether tomato cultivars host similar groups of organisms, as well as their effect on the community structure, particularly of those microbes with the potential to promote growth and/or control plant pathogens. Different cultivars of tomato (genotypes) host significantly different endophytic communities, which is also reflected at the order level. These communities are particularly rich in spore-forming bacteria that have the ability either to promote plant growth or synthetize antimicrobial compounds that deter plant pathogens. We conclude that the seeds of the tomato cultivars Elpida and Silverio are sources of endophytic bacteria capable of synthetizing antifungal substances that could potentially be used for biocontrol against plant-pathogenic fungi.