Silvina Marianela Yanil López

Draft Genome Sequence and Gene Annotation of Stemphylium lycopersici Strain CIDEFI-216

ABSTRACT Stemphylium lycopersici is a plant-pathogenic fungus that is widely distributed throughout the world. In tomatoes, it is one of the etiological agents of gray leaf spot disease. Here, we report the first draft genome sequence of S. lycopersici, including its gene structure and functional annotation.

The mitochondrial genome of the plantpathogenic fungus Stemphylium lycopersici uncovers a dynamic structure due to repetitive and mobile elements

Stemphylium lycopersici (Pleosporales) is a plant-pathogenic fungus that has been associated with a broad range of plant-hosts worldwide. It is one of the causative agents of gray leaf spot disease in tomato and pepper. The aim of this work was to characterize the mitochondrial genome of S. lycopersici CIDEFI-216, to use it to trace taxonomic relationships with other fungal taxa and to get insights into the evolutionary history of this phytopathogen. The complete mitochondrial genome was assembled into a circular double-stranded DNA molecule of 75,911 bp that harbors a set of 37 protein-coding genes, 2 rRNA genes (rns and rnl) and 28 tRNA genes, which are transcribed from both sense and antisense strands. Remarkably, its gene repertoire lacks both atp8 and atp9, contains a free-standing gene for the ribosomal protein S3 (rps3) and includes 13 genes with homing endonuclease domains that are mostly located within its 15 group I introns. Strikingly, subunits 1 and 2 of cytochrome oxidase are encoded by a single continuous open reading frame (ORF). A comparative mitogenomic analysis revealed the large extent of structural rearrangements among representatives of Pleosporales, showing the plasticity of their mitochondrial genomes. Finally, an exhaustive phylogenetic analysis of the subphylum Pezizomycotina based on mitochondrial data reconstructed their relationships in concordance with several studies based on nuclear data. This is the first report of a mitochondrial genome belonging to a representative of the family Pleosporaceae.

Antagonism of entomopathogenic fungi by Bacillus spp. associated with the integument of cicadellids and delphacids

Entomopathogenic fungi are potential tools to biocontrol cicadellids and delphacids, two groups of insects that cause extensive damage to agricultural crops. However, bacteria living on the host cuticle may inhibit fungal growth. In the present work, following the molecular characterization of 10 strains of Bacillus isolated from the integument of cicadellids and delphacids, we selected isolates of the fungi Beauveria bassiana and Metarhizium anisopliae that are resistant to the antimicrobials secreted by these bacterial strains. The antagonistic activity of the 10 bacterial isolates belonging to the genus Bacillus (i.e., B. amyloliquefaciens, B. pumilus, and B. subtilis) against 41 isolates of Bea. bassiana and 20 isolates of M. anisopliae was investigated in vitro on tryptic soy agar using the central disk test. With this approach, isolates of Bea. bassiana and M. anisopliae resistant to antagonistic bacteria were identified that can be further developed as biological control agents.

A survey on occurrence of Cladosporium fulvum identifies race 0 and race 2 in tomato-growing areas of Argentina

The presence of Cladosporium fulvum (syn. Passalora fulva), causal agent of tomato leaf mold, was confirmed in the two main greenhouse-production areas for tomato in Argentina. Using both morphological characters and internal transcribed spacer sequencing, we confirmed the presence of physiological races of this pathogen. A diagnostic multiplex polymerase chain reaction (PCR) was also developed, using primers derived from C. fulvum avirulence (Avr) genes. In all, 20 isolates of Cladosporium spp. were obtained as monospore cultures and 12 were identified as C. fulvum. By this method, we showed that, of these 12 isolates, 5 were race 0 (carrying functional Avr2, Avr4, Avr4E, and Avr9 genes) and 7 were race 2 (lacking the Avr2 gene). Race identity was confirmed by testing their virulence on a set of tomato differentials carrying different Cf resistance genes. All Avr genes could be amplified in single or multiplex PCR using DNA isolated from in vitro grown monospore cultures but only three Avr could be amplified when genomic DNA was isolated from C. fulvum-infected necrotic leaf tissue.

Screening of bacterial endophytes as potential biocontrol agents against soybean diseases

This research was aimed at identifying and characterizing endophytic micro‐organisms associated with soybean that have antimicrobial activity towards soybean pathogens.

Nodulation and Delayed Nodule Senescence: Strategies of Two Bradyrhizobium Japonicum Isolates with High Capacity to Fix Nitrogen

The purpose of this work was to study further two Bradyrhizobium japonicum strains with high nitrogen-fixing capacity that were identified within a collection of approximately 200 isolates from the soils of Argentina. Nodulation and nitrogen-fixing capacity and the level of expression of regulatory as well as structural genes of nitrogen fixation and the 1-aminocyclopropane-1-carboxylate (ACC) deaminase gene of the isolates were compared with that of E109-inoculated plants. Both isolates of B. japonicum, 163 and 366, were highly efficient to fix nitrogen compared to commercial strain E109. Isolate 366 developed a higher number and larger biomass of nodules and because of this fixed more nitrogen. Isolate 163 developed the same number and nodule biomass than E109. However, nodules developed by isolate 163 had red interiors for a longer period, had a higher leghemoglobin content, and presented high levels of expression of acdS gene, that codes for an ACC deaminase. In conclusion, naturalized rhizobia of the soils of Argentina hold a diverse population that might be the source of highly active nitrogen-fixing rhizobia, a process that appears to be based on different strategies.

Corynespora cassiicola and Stemphylium lycopersici infection and disease development on tomatoes in Argentina

Two pathogens were isolated from tomatoes with severe chlorosis and necrosis in northwestern Argentina. Monosporic cultures were morphologically characterised and molecularly identified as Stemphylium lycopersici and Corynespora cassiicola. This is the first report of C. cassiicola infecting tomato in Argentina.