Biocontrol potential of endophytic fungi originated from grapevine leaves for management of anthracnose disease caused by Colletotrichum gloeosporioides

Apple Bitter Rot: Biology, Ecology, Omics, Virulence Factors, and Management of Causal Colletotrichum Species

Apple bitter rot is caused by various Colletotrichum spp. that threaten apple production globally resulting in millions of dollars in damage annually. The fungus causes a decline in fruit quality and yield, eventually rotting the fruit and rendering it inedible. The pathogen is difficult to keep out of orchards because of its broad host range and transmissibility by rain splash and insects. Once the disease manifests, pathogen identification is difficult due to evolving taxonomy and similar morphology between species. Current management strategies are threatened by an increase in fungicide resistance and regulations on many multisite fungicides, leading to a pressing need for new management options for control. This review aims to summarise the most current knowledge regarding the biology, virulence factors, ecology, omics and emerging management strategies for Colletotrichum species that cause apple bitter rot.

TAXONOMY

Colletotrichum species-Domain Eukaryota, Kingdom Fungi, Phylum Ascomycota, Class Sordariomycetes, Order Glomerellales, Family Glomerellaceae, Genus Colletotrichum.

BIOLOGY

Hemibiotrophic pathogen with a wide host range that establishes a biotrophic interaction where it penetrates host plants using appressoria followed by a switch to necrotrophy causing rot symptoms.

TOXINS

Cercosporin, colletotrichins, colletotric acid, ferricrocin.

HOST RANGE

The host range varies by species but largely occurs on dicotyledonous plants and is less prevalent on monocots as well as gymnosperms, ferns, mosses and animals (e.g., insects).

DISEASE SYMPTOMS

Symptoms often manifest as flat to sunken necrotic areas on fruit. Lesions on leaves and fruit can have concentric rings with abundant pathogen sporulation.

DISEASE CONTROL

Colletotrichum spp. are primarily managed by single-site quinone outside inhibitor (Qol), methyl benzimidazole carbamate (MBC), demethylation inhibitor (DMI) fungicides, and multisite dithiocarbamate and phthalimide fungicides. Susceptibility may vary with species, strain specificity, or geographic region. Other management options include clean stock production, cultural practices, resistance breeding, and biological control through the introduction of protective or competing microorganisms.

Isolation of Antagonistic Endophytic Fungi from Postharvest Chestnuts and Their Biocontrol on Host Fungal Pathogens

In this study, antagonistic endophytic fungi were isolated from postharvest chestnut fruits; endophytic antagonistic fungi and their combination of inhibitory effects on the fungal pathogen Neofusicoccum parvum were evaluated. A total of 612 endophytic fungi were isolated from 300 healthy chestnut kernels, and 6 strains out of them including NS-3, NS-11, NS-38, NS-43, NS-56, and NS-58 were confirmed as antagonistic endophytic fungi against Neofusicoccum parvum; these were separately identified as Penicillium chermesinum, Penicillium italicum, Penicillium decaturense, Penicillium oxalicum, Talarmyces siamensis, and Penicillium guanacastense. Some mixed antagonistic endophytic fungi, such as NS-3-38, NS-11-38, NS-43-56, and NS-56-58-38, exhibited a much stronger antifungal activity against N. parvum than that applied individually. Among them, the mixture of NS-3-38 showed the highest antifungal activity, and the inhibition rate was up to 86.67%. The fermentation broth of NS-3, NS-38, and their combinations exhibited an obvious antifungal activity against N. parvum, and the ethyl acetate phase extract of NS-3-38 had the strongest antifungal activity, for which the inhibitory rate was up to 90.19%. The NS-3-38 fermentation broth combined with a chitosan coating significantly reduced N. parvum incidence in chestnuts from 100% to 19%. Furthermore, the fruit decay and weight loss of chestnuts during storage were significantly decreased by the NS-3-38 fermentation broth mixture along with a chitosan coating. Therefore, a mixture of P. chermesinum and P. decaturense could be used as a potential complex biocontrol agent to control postharvest fruit decay in chestnuts.

Assessment of the Entomopathogenic Potential of Fungal and Bacterial Isolates from Fall Armyworm Cadavers Against Spodoptera frugiperda Caterpillars and the Adult Boll Weevil, Anthonomus grandis

Increased attention is being focused on the biological control of agricultural pests using microorganisms, owing to their potential as a viable substitute for chemical control methods. Insect cadavers constitute a potential source of entomopathogenic microorganisms. We tested whether bacteria and fungi isolated from Spodoptera frugiperda (JE Smith) cadavers could affect its survival, development, egg-laying pattern, and hatchability, as well as induce mortality in Anthonomus grandis Boheman adults. We isolated the bacteria Enterobacter hormaechei and Serratia marcescens and the fungi Scopulariopsis sp. and Aspergillus nomiae from fall armyworm cadavers and the pest insects were subjected to an artificial diet enriched with bacteria cells or fungal spores to be tested, in the case of S. frugiperda, and only fungal spores in the case of A. grandis. Enterobacter hormaechei and A. nomiae were pathogenic to S. frugiperda, affecting the survival of adults and pupae. The fungus Scopulariopsis sp. does not affect the survival of S. frugiperda caterpillars and pupae; however, due to late action, moths and eggs may be affected. Aspergillus nomiae also increased mortality of A. grandis adults, as well as the development of S. frugiperda in the early stages of exposure to the diet, as indicated by the vertical spore transfer to offspring and low hatchability. Enterobacter hormaechei and A. nomiae are potential biocontrol agents for these pests, and warrant further investigation from a toxicological point of view and subsequently in field tests involving formulations that could improve agricultural sustainability practices.

Current Status and Future Perspectives on Distribution of Fungal Endophytes and Their Utilization for Plant Growth Promotion and Management of Grapevine Diseases

Grapevine is one of the economically most important fruit crops cultivated worldwide. Grape production is significantly affected by biotic constraints leading to heavy crop losses. Changing climatic conditions leading to widespread occurrence of different foliar diseases in grapevine. Chemical products are used for managing these diseases through preventive and curative application in the vineyard. High disease pressure and indiscriminate use of chemicals leading to residue in the final harvest and resistance development in phytopathogens. To mitigate these challenges, the adoption of potential biocontrol control agents is necessary. Moreover, multifaceted benefits of endophytes made them eco-friendly, and environmentally safe approach. The genetic composition, physiological conditions, and ecology of their host plant have an impact on their dispersion patterns and population diversity. Worldwide, a total of more than 164 fungal endophytes (FEs) have been characterized originating from different tissues, varieties, crop growth stages, and geographical regions of grapevine. These diverse FEs have been used extensively for management of different phytopathogens globally. The FEs produce secondary metabolites, lytic enzymes, and organic compounds which are known to possess antimicrobial and antifungal properties. The aim of this review was to understand diversity, distribution, host-pathogen-endophyte interaction, role of endophytes in disease management and for enhanced, and quality production.