Alternaria alternata Isolated from Infected Pears (Pyrus communis) in Italy Produces Non-Host Toxins and Hydrolytic Enzymes as Infection Mechanisms and Exhibits Competitive Exclusion against Botrytis cinerea in Co-Infected Host Fruits

Abstract

Alternaria alternata is one of the most devastating phytopathogenic fungi. This microorganism causes black spots in many fruits and vegetables worldwide, generating significant post-harvest losses. In this study, an A. alternata strain, isolated from infected pears (Pyrus communis) harvested in Italy, was characterized by focusing on its pathogenicity mechanisms and competitive exclusion in the presence of another pathogen, Botrytis cinerea. In in vitro assays, the fungus produces strong enzymatic activities such as amylase, xylanase, and cellulase, potentially involved during the infection. Moreover, it secretes four different toxins purified and identified as altertoxin I, alteichin, alternariol, and alternariol 4-methyl ether. Only alteichin generated necrotic lesions on host-variety pears, while all the compounds showed moderate to slight necrotic activity on non-host pears and other non-host fruit (lemon, Citrus limon), indicating they are non-host toxins. Interestingly, A. alternata has shown competitive exclusion to the competitor fungus Botrytis cinerea when co-inoculated in host and non-host pear fruits, inhibiting its growth by 70 and 65%, respectively, a result not observed in a preliminary characterization in a dual culture assay. Alteichin and alternariol 4-methyl ether tested against B. cinerea had the best inhibition activity, suggesting that the synergism of these toxins and enzymatic activities of A. alternata are probably involved in the competitive exclusion dynamics in host and non-host pear fruits.

Antifungal Activity of Ageritin, a Ribotoxin-like Protein from Cyclocybe aegerita Edible Mushroom, against Phytopathogenic Fungi

“…The fungal strains used in this work are listed in Table 1 . All the strains were isolated from naturally decayed fruits or plants in Italy and deposited in the fungal culture collection of the Biology Department of the University of Naples, Federico II, Italy [ 21 , 23 ]. Pure cultures were grown for 5 days at 25 ± 1 °C on PDA (potato dextrose agar) medium consisting of 200 g potato, 20 g dextrose, 20 g agar in 1 L water.…”

“…The antifungal activity of ageritin or quinoin was evaluated on potato dextrose agar (PDA) (Difco, Fisher Scientific Italia, Segrate (MI), Italy) as inhibition of mycelial radial growth using the method described previously [ 21 ] Briefly, 4 mm × 4 mm diameter mycelial plugs were cut from the edge of actively growing 6-day-old colonies, and one plug was placed in the center of a 5 cm diameter Petri dish with the mycelia in contact with the enzymes to be tested. Different amounts of ageritin (50, 100, and 200 μg/plug; 3.0, 6.0, and 12 nmole) or quinoin (200 and 400 μg/plug; 6.0 and 12 nmole) were dissolved in Milli-Q ultrapure water and applied separately to the top of each fungal plug.…”

Scope of Onsite, Portable Prevention Diagnostic Strategies for Alternaria Infections in Medicinal Plants

“…LAMP assay is a single-step method in which 4 to 6 primers bind the target sites laterally using a strand displacement Bst DNA polymerase, allowing amplification under isothermal conditions [114,115], as well as gel electrophoresis, turbidimeter, lateral flow dipstick, or the naked eye used for detecting amplified products [116]. LAMP assay was used for the rapid detection of Alternaria spp., including A. alternata, on infected pears [3,117]. LAMP can be applied in the field and in laboratories.…”

Bioprospection of Phytotoxic Plant-Derived Eudesmanolides and Guaianolides for the Control of Amaranthus viridis, Echinochloa crus-galli, and Lolium perenne Weeds

“…Bioherbicides were introduced into the market in the 1980s, and several new examples have been registered since then . Progress in this complex area and the discovery and study of new phytotoxic metabolites are ongoing, − while there are natural sources that are yet to be studied in depth. Progress is accentuated by the need to exploit compounds based on natural products due to restrictions on agricultural practices that are coming into force .…”