Analysis of plant cell death-inducing proteins of the necrotrophic fungal pathogens Botrytis squamosa and Botrytis elliptica

Fungal plant pathogens secrete proteins that manipulate the host in order to facilitate colonization. Necrotrophs have evolved specialized proteins that actively induce plant cell death by co-opting the programmed cell death machinery of the host. Besides the broad host range pathogen Botrytis cinerea, most other species within the genus Botrytis are restricted to a single host species or a group of closely related hosts. Here, we focused on Botrytis squamosa and B. elliptica, host specific pathogens of onion (Allium cepa) and lily (Lilium spp.), respectively. Despite their occurrence on different hosts, the two fungal species are each other's closest relatives. Therefore, we hypothesize that they share a considerable number of proteins to induce cell death on their respective hosts. In this study, we first confirmed the host-specificity of B. squamosa and B. elliptica. Then we sequenced and assembled high quality genomes. The alignment of these two genomes revealed a high level of synteny with few balanced structural chromosomal arrangements. To assess the cell death-inducing capacity of their secreted proteins, we produced culture filtrates of B. squamosa and B. elliptica that induced cell death responses upon infiltration in host leaves. Protein composition of the culture filtrate was analysed by mass spectrometry, and we identified orthologous proteins that were present in both samples. Subsequently, the expression of the corresponding genes during host infection was compared. RNAseq analysis showed that the majority of the orthogroups of the two sister species display similar expression patterns during infection of their respective host. The analysis of cell death-inducing proteins of B. squamosa and B. elliptica provides insights in the mechanisms used by these two Botrytis species to infect their respective hosts.

Perinaphthenone and derivatives as control agents of phytopathogenic fungi: fungitoxicity and metabolism

Metabolism and in vitro fungitoxicity of perinaphthenone against three economically important fungi of the citrus, Botryodiplodia spp., Botrytis spp. and Fusarium spp. were investigated. Perinaphthenone exhibited significant antifungal activity at 62.5 μM and above. Even, the inhibitory effect against Fusarium spp. was significantly enhanced by exposure to direct light. In addition, the metabolism of perinaphthenone by the three fungi was studied. Results show that perinaphthenone was transformed almost completely during the first 24 h; two major products, whose concentration increased progressively during the twelve days of the test, were isolated and identified as 2,3-dihydro-1H-phenalen-1-ol and 2,3-dihydro-phenalen-1-one. Although both metabolic products displayed a considerable fungistatic effect, their slightly lower activities in comparison to perinaphthenone indicate that the transformation was a detoxification process. Studies on the relationship between the effect of some substituents in the perinaphthenone core and the mycelial growth inhibition of Botryodiplodia spp. were also carried out. Results show that the α, β-unsaturated carbonyl system is an important structural requirement but not the only to be necessary for the strong antifungal activity of perinaphthenone. In general, the antifungal properties of perinaphthenone may be modulated through the incorporation of substituents in the naphthalene core or in the α, β-unsaturated carbonyl system. It is concluded that perinaphthenone could be used as an antifungal agent or as a structural template for the development of new fungicide compounds.

Triplex Real-Time PCR Approach for the Detection of Crucial Fungal Berry Pathogens-Botrytis spp., Colletotrichum spp. and Verticillium spp

Phytopathogens cause undeniably serious damage in agriculture by harming fruit cultivations and lowering harvest yields, which as a consequence substantially reduces food production efficiency. Fungi of the Botrytis, Colletotrichum and Verticillium genera are a main concern in berry production. However, no rapid detection method for detecting all of these pathogens simultaneously has been developed to date. Therefore, in this study, a multiplex real-time PCR assay for this purpose was established. Universal fungal primers for the D2 region of the large subunit ribosomal DNA and three multiplexable fluorogenic probes specific for the chosen fungi were designed and deployed. The triplex approach for the molecular detection of these fungi, which was developed in this study, allows for the rapid and effective detection of crucial berry pathogens, which contributes to a more rapid implementation of protective measures in plantations and a significant reduction in losses caused by fungal diseases.

Thyme and Savory Essential Oil Vapor Treatments Control Brown Rot and Improve the Storage Quality of Peaches and Nectarines, but Could Favor Gray Mold

The effect of biofumigation, through slow-release diffusors, of thyme and savory essential oils (EO), was evaluated on the control of postharvest diseases and quality of peaches and nectarines. EO fumigation was effective in controlling postharvest rots. Naturally contaminated peaches and nectarines were exposed to EO vapors for 28 days at 0 °C in sealed storage cabinets and then exposed at 20 °C for five days during shelf-life in normal atmosphere, simulating retail conditions. Under low disease pressure, most treatments significantly reduced fruit rot incidence during shelf-life, while, under high disease pressure, only vapors of thyme essential oil at the highest concentration tested (10% v/v in the diffusor) significantly reduced the rots. The application of thyme or savory EO favored a reduction of brown rot incidence, caused by Monilinia fructicola, but increased gray mold, caused by Botrytis cinerea. In vitro tests confirmed that M. fructicola was more sensitive to EO vapors than B. cinerea. Essential oil volatile components were characterized in storage cabinets during postharvest. The antifungal components of the essential oils increased during storage, but they were a low fraction of the volatile organic compounds in storage chambers. EO vapors did not influence the overall quality of the fruit, but showed a positive effect in reducing weight loss and in maintaining ascorbic acid and carotenoid content. The application of thyme and savory essential oil vapors represents a promising tool for reducing postharvest losses and preserving the quality of peaches and nectarines.