First report of Colletotrichum nymphaeae causing anthracnose on Hass avocados in Brazil.

The Hass cultivar is one of the most cultivated and distributed avocado varieties throughout the world, having high productivity, nutritional quality, market acceptance and adaptation to different climatic zones (Dreher and Davenport 2013). Anthracnose affects avocado production in tropical and subtropical regions, causing economic losses, especially post-harvest (Fuentes-Aragón et al. 2020). Correct identification of Colletotrichum species causing anthracnose is essential, as different species vary in important phenotypes such as virulence and sensitivity to fungicides (Chen et al. 2016). Twelve samples from batches of avocados with anthracnose were collected in Minas Gerais State, Brazil, in September 2023. The observed symptoms were brown to black depressed circular spots, ranging from a few millimeters to 3 cm in diameter on the epicarp of the fruits, covered in center by mucilaginous layers of pathogen sporulation. Isolation was performed directly from the spore masses and monoconidial isolates were cultured in PDA at 25°C for 7 days for morphological characterization and preserved in sterile water at 4°C. One of the morphotypes commonly recovered from lesions, represented by isolate UCBV 362 (Culture Collection COAD 3843), formed fast-growing colonies having white aerial mycelium and intense salmon-colored sporulation. The cylindrical conidia were 13 to 17.5 µm long and 4.5 to 7 µm wide (average 14.5 x 5.7 µm, N=100), produced on conidiophores dispersed in the aerial mycelium or aggregated on melanized conidiomata formed on the agar. The partial sequence of the second largest subunit of the RNA polymerase II gene (RPB2) from isolate UCBV 362 (GenBank: PQ034617, 1116 nt) showed 99% of coverage and 99.37% of nucleotide identity with the RPB2 sequence of the ex-epitype strain of Colletotrichum nymphaeae ICMP 17918 (=CBS 515.78) (GenBank: JN985506). In a Maximum Likelihood phylogenetic tree composed with RBP2 sequences from reference strains of the Colletotrichum acutatum species complex, the isolate UCBV 362 formed a highly supported clade with the ex-epitype and other reference strains of Colletotrichum nymphaeae, occupying the Clade 2 of the species complex together with C. scovillae and C. simmondsii (Damm et al. 2012). This result shows the reliability of RPB2 for phylogeny and species delimitation within Colletotrichum. To confirm pathogenicity, 10-mm discs from a 7-day-old colony were inoculated at 3 different points on healthy-looking avocado fruits and incubated at 28°C. Uninoculated fruits served as controls. The first symptoms appeared 5 days after inoculation and were similar to those observed in the original samples, while the fruits in the control group remained asymptomatic. The pathogen was reisolated from the lesions and identified morphologically, fulfilling Koch's postulates. Colletotrichum nymphaeae has been associated with avocado anthracnose in Mexico (Fuentes-Aragón et al. 2020). In Brazil, a study based on molecular phylogeny identified Colletotrichum siamense and C. karsti as etiological agents of this disease (Soares et al. 2021). This report expands the range of species that cause avocado anthracnose in Brazil and provides etiological information for the implementation and monitoring of control methods, especially chemical control.

The antifungal activity and mechanism of silver nanoparticles against four pathogens causing kiwifruit post-harvest rot.

Post-harvest rot causes enormous economic loss to the global kiwifruit industry. Currently, there are no effective fungicides to combat the disease. It is unclear whether silver nanoparticles (AgNPs) are effective in controlling post-harvest rot and, if so, what the underlying antifungal mechanism is. Our results indicated that 75 ppm AgNPs effectively inhibited the mycelial growth and spore germination of four kiwifruit rot pathogens: Alternaria alternata, Pestalotiopsis microspora, Diaporthe actinidiae, and Botryosphaeria dothidea. Additionally, AgNPs increased the permeability of mycelium's cell membrane, indicating the leakage of intracellular substance. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations revealed that AgNPs induced pathogen hypha shrinkage and distortion, as well as vacuolation in hypha cells, implying that AgNPs caused cellular and organelle structural degradation. The transcriptome sequencing of mycelium treated with AgNPs (24 h / 48 h) was performed on the Illumina Hiseq 4000 sequencing (RNA-Seq) platform. For the time points of 24 h and 48 h, AgNPs treatment resulted in 1,178 and 1,461 differentially expressed genes (DEGs) of A. alternata, 517 and 91 DEGs of P. microspora, 1,287 and 65 DEGs of D. actinidiae, 239 and 55 DEGs of B. dothidea, respectively. The DEGs were found to be involved in "catalytic activity," "small molecule binding," "metal ion binding," "transporter activity," "cellular component organization," "protein metabolic process," "carbohydrate metabolic process," and "establishment of localization." Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis also revealed that "carbohydrate metabolism," "amino acid metabolism," "energy metabolism," and "xenobiotics biodegradation and metabolism" of "metabolism processes" were the most highly enriched pathways for these DEGs in four pathogens, with "cellular processes" being particularly enriched for B. dothidea. Furthermore, quantitative polymerase chain reactions (qPCRs) were used to validate the RNA-seq results. It was also confirmed that AgNPs could significantly reduce the symptoms of kiwifruit rot without leaving any Ag+ residue on the peel and flesh of kiwifruit. Our findings contributed to a better understanding of the antifungal effect and molecular mechanisms of AgNPs against pathogens causing kiwifruit post-harvest rot, as well as a new perspective on the application of this novel antifungal alternative to fruit disease control.

Field application of Bacillus subtilis and Aureobasidium pullulans to reduce Monilinia laxa post-harvest rot on cherry.

Brown rot caused by Monilinia spp. is one of the most important diseases in stone fruits worldwide. Latent infections of fruit by the pathogen often manifest once the fruit is ripe, leading to post-harvest rots. Two microbial strains (Bacillus subtilis -B91 and Aureobasidium pullulans - Y126) have shown antagonistic properties against M. laxa in previous studies. This study assessed the reduction in post-harvest rot of cherry by M. laxa when the two biocontrol (BCAs) strains were applied pre-harvest under field conditions to fruit artificially inoculated with M. laxa. The experiment was carried out for two consecutive years in cherry orchards in Kent. When applied pre-harvest, both strains (B91 and Y126) reduced the incidence of post-harvest rots by 30% - 60%. This promising result helps towards the commercialisation of the two strains, which would reduce reliance on fungicides in commercial cherry production. Supplementary Information: The online version contains supplementary material available at 10.1007/s10658-022-02508-8.

Edible Chitosan/Propolis Coatings and Their Effect on Ripening, Development of Aspergillus flavus, and Sensory Quality in Fig Fruit, during Controlled Storage.

Biodegradable alternatives for the control of Aspergillus flavus in fig fruit were tested with the application of coatings based on chitosan (CS) and propolis (P). To potentiate the fungicidal effect, nanoparticles of these two (CSNPs and PNPs) were also considered. The objectives of this research were to evaluate the effect of different formulations on: (a) the ripening process of the fig, (b) the incidence of A. flavus and the production of aflatoxins, and (c) the acceptance of the treated fruit by a panel. The nanostructured coatings did not influence the ripening process of the fruit during the 12 days of storage, however, the antioxidant activity increased by approximately 30% with the coating CS + PNPs + P. The figs treated with CS + CSNPs + PNPs + P, inhibited the growth of the fungus by about 20% to 30% under laboratory and semi-commercial conditions. For all treatments, the aflatoxin production was lower than 20 ppb compared to the control with values of c.a. 250 ppb. The sensory quality was acceptable among the panel. The edible coatings can be a non-toxic alternative for post-harvest preservation and the consumption of fig fruit. The next step will be its inclusion and evaluation at a commercial level in packing houses.

Efficacy of Oryza sativa husk and Quercus phillyraeoides extracts for the in vitro and in vivo control of fungal rot disease of white yam (Dioscorea rotundata Poir).

Tuber rot disease is a major constraint to white yam (Dioscorea rotundata) production, accounting for 50-60% of annual yield losses in Nigeria. The main method of control using synthetic fungicides is being discouraged due to human and environmental health hazards. The potential of Oryza sativa husk (OSH) and Quercus phillyraeoides (QP) extracts for the in vitro and in vivo control of six virulent rot-causing fungal pathogens, Lasiodiplodia theobromae, Aspergillus niger, Rhizoctonia solani, Penicillium oxalicum, Sclerotium rolfsii, and Fusarium oxysporum was evaluated, using five different extract concentrations of 0.5%, 1.0%, 1.5%, 2.5%, and 3.5% w/v. These fungi were isolated from rotted tubers of D. rotundata, across three agroecological zones in Nigeria-the Humid rainforest, Derived savanna, and southern Guinea savanna. All treatments were subjected to three methods of inoculation 48 hours before the application of both extracts and stored at 28 ± 2°C for 6 months. Radial mycelial growth of the test pathogens was effectively inhibited at concentrations ≤ 3.5% w/v in vitro for both OSH and QP extracts. Rotting was significantly reduced (P ≤ 0.05) to between 0 to 18.8% and 0% to 20.9% for OSH and QP extracts respectively. The extracts significantly (P ≤ 0.05) inhibited percent rot of the test pathogens at 3.5% concentration w/v in vivo. Rot incidence was, however, lower in replicate tubers that were inoculated, treated with extracts and exposed than treatments that were covered. Phytochemical analysis of OSH and QP extracts revealed the presence of secondary metabolites such as alkaloids, flavonoids, saponins, tannins, ferulic acid, phlobatanins, Terpenoids, phenols, anthraquinone and pyroligneous acid. The efficacy of both extracts in reducing rot in this study recommends their development as prospective biopesticide formulation and use in the management of post-harvest rot of yam tubers.