Using essential oils to control diseases in strawberries and peaches.

Strawberry and peach crops are of great economic and social importance, mainly due to the added value and income generation for small and medium producers in different regions of Brazil. Some fungal diseases can compromise the final profitability of production, such as those caused by Colletotrichum sp., Botrytis cinerea and Monilinia fructicola fungi. The control of these pathogens mainly occurs through fungicides, which has been generating concern for consumers, as well as biological imbalance and environmental contamination. The need for new alternatives for disease control has been leading to more research being conducted on essential oils. Our scientific questions were based on a compilation of experiments which revealed the efficiency of essential oils in disease control. With the purpose of evaluating the fungicidal activity of Aloysia citriodora, Cymbopogon winterianus, Lippia alba and Ocimum americanum essential oils on the control of fungi, such as Colletotrichum sp., Botrytis cinerea and Monilinia fructicola in vitro and in the post-harvest of fruits, this work was developed at the Federal University of Santa Maria, Frederico Westphalen county (Rio Grande do Sul state), Brazil, from 2016 to 2018. The following evaluations were done: (i) characterization of essential oil doses in vitro for controlling Colletotrichum sp., Botrytis cinerea and Monilinia fructicola fungi, and (ii) determination of the minimum inhibitory concentration (Ω, mL/L) of essential oils in post-harvest of strawberries and peaches. All essential oils have high fungicidal activity in vitro experiments. The A. citriodora, L. alba and O. americanum essential oils had a satisfactory effect for post-harvest controlling of Colletotrichum sp. C. winterianus and O. americanum. The essential oils promoted satisfactory post-harvest control of Botrytis cinerea in strawberries. All essential oils have high fungitoxicity against Monilinia fructicola in vitro and post-harvest, highlighting the greater efficiency of A. citriodora essential oil in peaches. The essential oils present high fungitoxicity for controlling diseases in strawberries and peaches, presenting high potential performance for formulating commercial fungicide.

Synthesis and evaluation of aromatic methoxime derivatives against five postharvest phytopathogenic fungi of fruits. Main structure-activity relationships.

The antifungal activity of a library of twenty-four aromatic methoximes was examined against five representative postharvest phytopathogenic fungi. The panel included Penicillium digitatum, Penicillium italicum, Rhizopus stolonifer, Botrytis cinerea and Monilinia fructicola, all of which cause relevant economic losses worldwide as a result of affecting harvested fruits. The minimum inhibitory concentrations and minimum fungicidal concentrations of each compound were defined and the main structure-activity relationships were determined. Although other congeners were more potent, drug likeliness considerations pointed to the methoxime derived from 2,4-dihydroxypropiophenone as the compound with the most suitable profile. The morphology of the colonies of the fungal strains treated with the methoxime was examined microscopically and the compound was also tested in freshly harvested peaches and oranges, exhibiting promising control profiles in both fruits, similar to those of the commercial agents Imazalil and Carbendazim.

ß-Fructofuranosidase and ß -D-Fructosyltransferase from New Aspergillus carbonarius PC-4 Strain Isolated from Canned Peach Syrup: Effect of Carbon and Nitrogen Sources on Enzyme Production.

ß-fructofuranosidase (invertase) and ß-D-fructosyltransferase (FTase) are enzymes used in industrial processes to hydrolyze sucrose aiming to produce inverted sugar syrup or fructooligosaccharides. In this work, a black Aspergillus sp. PC-4 was selected among six filamentous fungi isolated from canned peach syrup which were initially screened for invertase production. Cultivations with pure carbon sources showed that invertase and FTase were produced from glucose and sucrose, but high levels were also obtained from raffinose and inulin. Pineapple crown was the best complex carbon source for invertase (6.71 U/mL after 3 days of cultivation) and FTase production (14.60 U/mL after 5 days of cultivation). Yeast extract and ammonium chloride nitrogen sources provided higher production of invertase (6.80 U/mL and 6.30 U/mL, respectively), whereas ammonium nitrate and soybean protein were the best nitrogen sources for FTase production (24.00 U/mL and 24.90 U/mL, respectively). Fermentation parameters for invertase using yeast extract were Y P/S = 536.85 U/g and P P = 1.49 U/g/h. FTase production showed values of Y P/S = 2,627.93 U/g and P P = 4.4 U/h using soybean protein. The screening for best culture conditions showed an increase of invertase production values by 5.10-fold after 96 h cultivation compared to initial experiments (fungi bioprospection), while FTase production increased by 14.60-fold (44.40 U/mL) after 168 h cultivation. A. carbonarius PC-4 is a new promising strain for invertase and FTase production from low cost carbon sources, whose synthesized enzymes are suitable for the production of inverted sugar, fructose syrups, and fructooligosaccharides.

Comparative proteomic and metabolomic studies between Prunus persica genotypes resistant and susceptible to Taphrina deformans suggest a molecular basis of resistance.

The worldwide-distributed leaf peach curl disease is caused by the biotroph Taphrina deformans. To characterize the plant-fungus interaction, resistant and susceptible Prunus persica genotypes grown in the orchard were studied. Asymptomatic leaves were tested for fungal presence. In all resistant leaves analyzed the fungus was not detected. Conversely, leaves from the susceptible genotype were categorized according to the presence or absence of the pathogen. Comparative metabolomic analysis disclosed the metabolite composition associated with resistant and susceptible interactions, and of compounds involved in fungal growth inhibition such as chlorogenic acid, whose in vitro antifungal activity was verified in this work. Differential proteome studies revealed that chloroplasts are important site of plant defense responses against T. deformans. Members of the Bet-v1-like family protein differentially responded to the pathogen. Extracellular pathogenesis-related proteins, evaluated by qRT-PCR, and an enone oxidoreductase are constitutively present in leaves of resistant trees and could be related to fungal resistance. This study is a global view of the changes in the metabolome, proteome and transcripts related to plant defense in naturally infected leaves of susceptible plants during the asymptomatic stage. Additionally, it provides clues to the successful molecular mechanisms operating in resistant plants, which neither develop the disease nor harbor the pathogen.

Unravelling early events in the Taphrina deformans-Prunus persica interaction: an insight into the differential responses in resistant and susceptible genotypes.

Leaf peach curl is a devastating disease affecting leaves, flowers and fruits, caused by the dimorphic fungus Taphrina deformans. To gain insight into the mechanisms of fungus pathogenesis and plant responses, leaves of a resistant and two susceptible Prunus persica genotypes were inoculated with blastospores (yeast), and the infection was monitored during 120 h post inoculation (h.p.i.). Fungal dimorphism to the filamentous form and induction of reactive oxygen species (ROS), callose synthesis, cell death and defence compound production were observed independently of the genotype. Fungal load significantly decreased after 120 h.p.i. in the resistant genotype, while the pathogen tended to grow in the susceptible genotypes. Metabolic profiling revealed a biphasic re-programming of plant tissue in susceptible genotypes, with an initial stage co-incident with the yeast form of the fungus and a second when the hypha is developed. Transcriptional analysis of PRs and plant hormone-related genes indicated that pathogenesis-related (PR) proteins are involved in P. persica defence responses against T. deformans and that salicylic acid is induced in the resistant genotype. Conducted experiments allowed the elucidation of common and differential responses in susceptible versus resistant genotypes and thus allow us to construct a picture of early events during T. deformans infection.

Species of the Colletotrichum acutatum complex associated with anthracnose diseases of fruit in Brazil.

Although Colletotrichum acutatum was recently investigated and shown to be a species complex comprising about 30 species, the name is still used in its broad sense for anthracnose pathogens of fruits in Brazil. In this study, a multilocus molecular analysis was carried out based on a dataset of ITS, HIS3, GAPDH, CHS-1, TUB2 and ACT sequences of Colletotrichum strains belonging to the C. acutatum species complex from fruits collected in different regions in Brazil combined with sequences of ex-type and other reference strains of species belonging to this complex. The strains were revealed to belong to Colletotrichum nymphaeae, Colletotrichum melonis, Colletotrichum abscissum and one new species, namely Colletotrichum paranaense, from apple and peach. Morphological descriptions of the new species and a strain closely related to but diverging from C. melonis are provided. From the data presently available, the most common species on apple fruits in Brazil is C. nymphaeae. In a pathogenicity test, strains of all four species caused lesions on detached apple, peach and guava fruits, except for strain CBS 134730 that did not infect guava fruits.

Eradicant and curative treatments of hexanal against peach brown rot

Brown rot, caused by Monilinia spp. , is one of the most important peach (Prunuspersica (L.) Batsch) diseases and the main cause of postharvest losses. Currently, alternative methods for postharvest disease control, such as the use of volatiles, are under investigation. The objective of this study was to determine the effects of hexanal on the in vitro development of Monilinia fructicola and M. laxa and on monocyclic components of brown rot on peaches. To evaluate the effect on pathogen development in vitro, a single dose of 215 µL of liquid hexanal was placed on glass jars in closed plastic containers (4.3 L) at the moment of fungi transfer, 24 or 48 h after transferring to Petri dishes. After hexanal application, the Petri dishes were kept inside the containers that were closed for 24 h at 20 ºC. Mycelial growth was measured seven days after hexanal removal. For in vivo assays, inoculated fruits were kept in closed plastic containers, and hexanal was applied at the moment of fruit inoculation or 24 hours thereafter. The monocyclic components infection frequency, expressed as brown rot incidence, lesion diameter and lesion sporulation, were assessed daily for seven days. Overall, hexanal was more effective in inhibiting mycelial growth when applied at the moment of pathogen transfer. Hexanal did not prevent pathogen infection, but reduced lesion diameter and completely inhibited spore production on the fruit for both treatments. Hexanal provides a promising alternative for chemical control and can be used in postharvest handling systems.

Eradicant and curative treatments of hexanal against peach brown rot

Brown rot, caused by Monilinia spp. , is one of the most important peach (Prunuspersica (L.) Batsch) diseases and the main cause of postharvest losses. Currently, alternative methods for postharvest disease control, such as the use of volatiles, are under investigation. The objective of this study was to determine the effects of hexanal on the in vitro development of Monilinia fructicola and M. laxa and on monocyclic components of brown rot on peaches. To evaluate the effect on pathogen development in vitro, a single dose of 215 µL of liquid hexanal was placed on glass jars in closed plastic containers (4.3 L) at the moment of fungi transfer, 24 or 48 h after transferring to Petri dishes. After hexanal application, the Petri dishes were kept inside the containers that were closed for 24 h at 20 ºC. Mycelial growth was measured seven days after hexanal removal. For in vivo assays, inoculated fruits were kept in closed plastic containers, and hexanal was applied at the moment of fruit inoculation or 24 hours thereafter. The monocyclic components infection frequency, expressed as brown rot incidence, lesion diameter and lesion sporulation, were assessed daily for seven days. Overall, hexanal was more effective in inhibiting mycelial growth when applied at the moment of pathogen transfer. Hexanal did not prevent pathogen infection, but reduced lesion diameter and completely inhibited spore production on the fruit for both treatments. Hexanal provides a promising alternative for chemical control and can be used in postharvest handling systems.(AU)