A Sequence Resource of Autosomes and Additional Chromosomes in the Peach Pathotype of Alternaria alternata

Phylogenomic analyses of Alternaria section Alternaria: A high-resolution, genome-wide study of lineage sorting and gene tree discordance

The genus Alternaria contains a diversity of saprobic and pathogenic species that can be found in a wide range of environments. Alternaria is currently divided into 26 subgeneric sections, and the "small-spored" Alternaria section Alternaria includes many species that are economically important agricultural pathogens. Recognizing that a stable framework for systematics and species identification is essential for management and regulation purposes, this section has experienced much taxonomic debate and systematic revision in recent years. Molecular phylogenetic studies have challenged the reliability of using morphological characteristics to differentiate Alternaria species but have also suggested that commonly used molecular markers for fungal phylogenetics may not be sufficiently informative at this taxonomic level. To allow the assessment of molecular variation and evolutionary history at a genome-wide scale, we present an overview and analysis of phylogenomic resources for Alternaria section Alternaria. We review the currently available genomic resources and report five newly sequenced genomes. We then perform multiple comparative genomic analyses, including macrosynteny assessment and inference of phylogenetic relationships using a variety of data sets and analysis methods. Fine-scale, genome-wide phylogenetic reconstruction revealed incomplete lineage sorting and the genomic distribution of gene/species tree discordance. Based on these patterns, we propose a list of candidate genes that may be developed into informative markers that are diagnostic for the main lineages. This overview identifies gaps in knowledge and can guide future genome sequencing efforts for this important group of plant pathogenic fungi.

Production of Alternaria Toxins in Yellow Peach (Amygdalus persica) upon Artificial Inoculation with Alternaria alternate

The yellow peach (Amygdalus persica), an important fruit in China, is highly susceptible to infection by Alternaria sp., leading to potential health risks and economic losses. In the current study, firstly, yellow peaches were artificially inoculated with Alternariaalternate. Then, the fruits were stored at 4 °C and 28 °C to simulate the current storage conditions that consumers use, and the Alternaria toxins (ATs) contents from different parts of the fruits were analyzed via ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The results showed that the growth of A. alternate and the ATs production were dramatically affected by the storage temperature. At 28 °C, the fungi grew rapidly and the lesion diameter reached about 4.0 cm within 15 days of inoculation, while, at 4 °C, the fungal growth was noticeably inhibited, with no significant change in the lesion diameter. To our surprise, high contents of ATs were produced under both storage conditions even though the fungal growth was suppressed. With an increase in the incubation time, the amounts of ATs showed a steady tendency to increase in most cases. Remarkably, alternariol monomethyl ether (AME), alternariol (AOH), and tenuazonic acid (TeA) were detected in the rotten tissue and also in the surrounding tissue, while a large amount of TeA could also be found in the healthy tissue. To the best of our knowledge, this is the first report regarding the production of ATs by the infection of Alternaria sp. in yellow peach fruits via artificial inoculation under regulated conditions, and, based on the evidence herein, it is recommended that ATs be included in monitoring and control programs of yellow peach management and food safety administration.

Alternaria Leaf Spot Caused by Alternaria Species: An Emerging Problem on Ornamental Plants in Italy

Serious outbreaks of Alternaria leaf spot and plant decay have recently been recorded on several ornamental plants in the Biella Province (Northern Italy). Twenty-two fungal isolates were obtained from Alternaria infected plant tissues from 13 ornamental hosts. All the isolates were identified morphologically as small-spored Alternaria species. Multilocus sequence typing, carried out by means of ITS, rpb2, tef1, endoPG, Alt a 1, and OPA10-2, assigned 19 isolates as Alternaria alternata, two isolates as belonging to the Alternaria arborescens species complex, and one isolate as an unknown Alternaria sp. Haplotype analyses of ornamental and reference A. alternata isolates from 12 countries identified 14 OPA10-2 and 11 endoPG haplotypes showing a relatively high haplotype diversity. A lack of host specialization or geographic distribution was observed. The host range of the studied A. alternata isolates expanded in cross-pathogenicity assays, and more aggressiveness was frequently observed on the experimental plants than on the host plants from which the fungal isolates were originally isolated. High disease severity, population expansion, intraspecies diversity, and increased range of experimental hosts were seen in the emergence of Alternaria disease on ornamentals. More epidemiological and molecular studies should be performed to better understand these diseases, taking into consideration factors such as seed transmission and ongoing climate changes.