Monilinia species are among the most devastating fungi worldwide as they cause brown rot and blossom blight on fruit trees. To understand the molecular bases of their pathogenic lifestyles, we compared the newly assembled genomes of single strains of Monilinia fructicola, M. fructigena and M. laxa, with those of Botrytis cinerea and Sclerotinia sclerotiorum, as the closest species within Sclerotiniaceae. Phylogenomic analysis of orthologous proteins and syntenic investigation suggest that M. laxa is closer to M. fructigena than M. fructicola, and is closest to the other investigated Sclerotiniaceae species. This indicates that M. laxa was the earliest result of the speciation process. Distinct evolutionary profiles were observed for transposable elements (TEs). M. fructicola and M. laxa showed older bursts of TE insertions, which were affected (mainly in M. fructicola) by repeat-induced point (RIP) mutation gene silencing mechanisms. These suggested frequent occurrence of the sexual process in M. fructicola. More recent TE expansion linked with low RIP action was observed in M. fructigena, with very little in S. sclerotiorum and B. cinerea. The detection of active non-syntenic TEs is indicative of horizontal gene transfer and has resulted in alterations in specific gene functions. Analysis of candidate effectors, biosynthetic gene clusters for secondary metabolites and carbohydrate-active enzymes, indicated that Monilinia genus has multiple virulence mechanisms to infect host plants, including toxins, cell-death elicitor, putative virulence factors and cell-wall-degrading enzymes. Some species-specific pathogenic factors might explain differences in terms of host plant and organ preferences between M. fructigena and the other two Monilinia species.
Anthracnose of papaya (Carica papaya L.) caused by the fungus Colletotrichum spp. is one of the most economically important postharvest diseases. Coating with chitosan (CS) and Ruta graveolens essential oil (REO) might represent a novel eco-friendly method to prevent postharvest anthracnose infection. These compounds show both antimicrobial and eliciting activities, although the molecular mechanisms in papaya have not been investigated to date. In this study, the effectiveness of CS and REO alone and combined (CS-REO) on postharvest anthracnose of papaya fruit during storage were investigated, along with the expression of selected genes involved in plant defense mechanisms. Anthracnose incidence was reduced with CS, REO, and CS-REO emulsions after 9 days storage at 25°C, by 8, 21, and 37%, respectively, with disease severity reduced by 22, 29, and 44%, respectively. Thus, McKinney’s decay index was reduced by 22, 30, and 44%, respectively. A protocol based on reverse transcription quantitative real-time PCR (RT-qPCR) was validated for 17 papaya target genes linked to signaling pathways that regulate plant defense, pathogenesis-related protein, cell wall-degrading enzymes, oxidative stress, abiotic stress, and the phenylpropanoid pathway. CS induced gene upregulation mainly at 6 h posttreatment (hpt) and 48 hpt, while REO induced the highest upregulation at 0.5 hpt, which then decreased over time. Furthermore, CS-REO treatment delayed gene upregulation by REO alone, from 0.5 to 6 hpt, and kept that longer over time. This study suggests that CS stabilizes the volatile and/or hydrophobic substances of highly reactive essential oils. The additive effects of CS and REO were able to reduce postharvest decay and affect gene expression in papaya fruit.
Although the chestnut mosaic disease (ChMD) was described several decades ago, its etiology is still not elucidated. Here, using classical approaches in combination with high throughput sequencing (HTS) techniques, we identify a novel Badnavirus that is a strong etiological candidate for ChMD. Two disease sources from Italy and France were submitted to HTS-based viral indexing. Total RNAs were extracted, ribodepleted and sequenced on an Illumina NextSeq500 (2x150 or 2x 75 nt). In each source, we identified a single contig of about 7.2 kilobases that corresponds to a complete circular viral genome and shares homologies with various badnaviruses. The genomes of the two isolates have an average nucleotide identity of 90.5% with a typical badnaviral genome organization comprising three open reading frames. Phylogenetic analyses and sequence comparisons show that this virus is a novel species for which we propose the name Chestnut mosaic virus (ChMV). Using a newly developed molecular detection test, we systematically detected the virus in symptomatic graft-inoculated indicator plants (chestnut and American oak), as well in chestnut trees presenting typical ChMD symptoms in the field (100% and 87% in France and Italy surveys, respectively). Datamining of publicly available chestnut SRA transcriptomic data allowed the reconstruction of two additional complete ChMV genomes from two Castanea mollissima sources from the USA, as well as ChMV detection in C. dentata from the USA. Preliminary epidemiological studies, performed in France and in Central Eastern Italy, showed that ChMV has a high incidence in some commercial orchards, with a low within-orchard genetic diversity.
Subtropical fruit such as avocados (Persea americana), mangoes (Mangifera indica L.), and papayas (Carica papaya L.) are economically important in international trade and predominantly exported to European destinations. These fruits are highly consumed due to their health benefits. However, due to long-distance shipping and the time required to reach the retail department stores, postharvest losses, due to postharvest decay occurring during the supply chain, affect the fruit quality on arrival at the long-distance distribution points. Currently, the use of synthetic fungicide, Prochloraz®, is used at the packing line to reduce postharvest decay and retain the overall quality of mangoes and avocados. Due to the ban imposed on the use of synthetic fungicides on fresh fruit, several studies have focused on the development of alternative technologies to retain the overall quality during marketing. Among the developed alternative technologies for commercial adoption is the use of edible coatings, such as chitosan biocontrol agents and essential oil vapors. The objective of this review is to summarize and analyze the recent advances and trends in the use of these alternative postharvest treatments on anthracnose decay in avocados, mangoes, and papayas.
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