Corynespora cassiicola f. sp. schinii, a Potential Biocontrol Agent for the Weed Schinus terebinthifolius in the United States

Evaluation of foliar fungus-mediated interactions with below and aboveground enemies of the invasive plant Ageratina adenophora

Plant-fungal associations are frequently key drivers of plant invasion success. Foliar fungi can benefit their invasive hosts by enhancing growth promotion, disease resistance and environmental stress tolerance. However, the roles of foliar fungi may vary when a given invasive plant faces different stresses. In this study, we designed three independent experiments to evaluate the effects of a foliar fungus, Colletotrichum sp., on the growth performance of the invasive plant Ageratina adenophora under different soil conditions, as well as the responses of A. adenophora to the foliar fungal pathogen Diaporthe helianthi and to herbivory. We found that the soil type was the most influential factor for the growth of A. adenophora. The role of the foliar fungus Colletotrichum sp. varied in the different soil types but generally adversely affected leaf development in A. adenophora. Colletotrichum sp. may be a weak latent foliar pathogen that can enhance the pathogenicity of D. helianthi on leaves of A. adenophora and marginally reduce signs of herbivory by natural insects in the wild on A. adenophora seedlings. In general, the benefits of the foliar fungus Colletotrichum to the fitness of A. adenophora are not significant in the context of this experimental design. However, our data highlight the need to consider both aboveground and belowground biota in different soil habitats when evaluating the effects of foliar fungi.

Phylogenetic Diversity and Host Specialization of Corynespora cassiicola Responsible for Emerging Target Spot Disease of Cotton and Other Crops in the Southeastern United States

Corynespora cassiicola is a ubiquitous fungus causing emerging plant diseases worldwide, including target spot of cotton, soybean, and tomato, which have rapidly increased in incidence and severity throughout the southeastern United States. The objectives of this study were to understand the causes for the emerging target spot epidemics in the United States by comparing phylogenetic relationships of isolates from cotton, tomato, soybean, and other crop plants and ornamental hosts, and through the determination of the host range of isolates from emerging populations. Fifty-three isolates were sampled from plants in the southeastern United States and 1,380 nucleotides from four nuclear loci were sequenced. Additionally, sequences of the same loci from 23 isolates representing each of the distinct lineages of C. cassiicola described from previous studies were included. Isolates clustered based on host of origin, regardless of the geographic location of sampling. There was no genetic diversity detected among isolates from cotton, which were genetically distinct from isolates from other host species. Furthermore, pathogenicity and virulence assays of 40 isolates from various hosts onto cotton, soybean, tomato, and cucumber showed that isolates from cotton were more aggressive to cotton than those from other hosts. Soybean and tomato were most susceptible to isolates that originated from the same host, providing evidence of host specialization. These results suggest that emerging target spot epidemics in the United States are caused by either the introduction of host-specific isolates or the evolution of more aggressive strains on each host.

Genome sequences and SNP analyses of Corynespora cassiicola from cotton and soybean in the southeastern United States reveal limited diversity

Corynespora cassiicola attackes diverse agriculturally important plants, including soybean and cotton, in the US. It is a reemerge pathogen on cotton in southeastern US. Whole genome sequences of four cotton and one soybean isolate from Tennessee were used to develop single nucleotide polymorphism markers for cotton isolates. Cotton isolates had little diversity at the genome level and very little differentiation from the soybean isolate. Analysis of 75 isolates from cotton and soybean, using targeted-sequencing of 22 polymorphic SNP sites, revealed eight multi-locus genotypes and it appears a single clonal lineage predominates across the southeastern region. The cotton and soybean genome sequences were significantly different from the public reference genome derived from a rubber isolate and the utility of these novel resources will be discussed.

All that glitters is not Ramularia

Ramularia is a species-rich genus that harbours plant pathogens responsible for yield losses to many important crops, including barley, sugar beet and strawberry. Species of Ramularia are hyphomycetes with hyaline conidiophores and conidia with distinct, thickened, darkened, refractive conidiogenous loci and conidial hila, and Mycosphaerella sexual morphs. Because of its simple morphology and general lack of DNA data in public databases, several allied genera are frequently confused with Ramularia. In order to improve the delimitation of Ramularia from allied genera and the circumscription of species within the genus Ramularia, a polyphasic approach based on multilocus DNA sequences, morphological and cultural data were used in this study. A total of 420 isolates belonging to Ramularia and allied genera were targeted for the amplification and sequencing of six partial genes. Although Ramularia and Ramulariopsis proved to be monophyletic, Cercosporella and Pseudocercosporella were polyphyletic. Phacellium isolates clustered within the Ramularia clade and the genus is thus tentatively reduced to synonymy under Ramularia. Cercosporella and Pseudocercosporella isolates that were not congeneric with the ex-type strains of the type species of those genera were assigned to existing genera or to the newly introduced genera Teratoramularia and Xenoramularia, respectively. Teratoramularia is a genus with ramularia-like morphology belonging to the Teratosphaeriaceae, and Xenoramularia was introduced to accommodate hyphomycetous species closely related to Zymoseptoria. The genera Apseudocercosporella, Epicoleosporium, Filiella, Fusidiella, Neopseudocercosporella, and Mycosphaerelloides were also newly introduced to accommodate species non-congeneric with their purported types. A total of nine new combinations and 24 new species were introduced in this study.