Morphological and chemical characterization of Alternaria populations from apple fruit

Carvacrol Treatment Reduces Decay and Maintains the Postharvest Quality of Red Grape Fruits (Vitis vinifera L.) Inoculated with Alternaria alternata

In this study, we isolated and identified pathogenic fungi from the naturally occurring fruits of red grapes, studied their biological characteristics, screened fifteen essential oil components to find the best natural antibacterial agent with the strongest inhibitory effect, and then compared the incidence of postharvest diseases and storage potential of red grapes treated with two concentrations (0.5 EC50/EC50) of essential oil components (inoculated with pathogenic fungi) during storage for 12 d at room temperature. In our research, Alternaria alternata was the primary pathogenic fungus of red grapes. Specifically, red grapes became infected which caused diseases, regardless of whether they were inoculated with Alternaria alternata in an injured or uninjured state. Our findings demonstrated that the following conditions were ideal for Alternaria alternata mycelial development and spore germination: BSA medium, D-maltose, ammonium nitrate, 28 °C, pH 6, and exposure to light. For the best Alternaria alternata spore production, OA medium, mannitol, urea, 34 °C, pH 9, and dark conditions were advised. Furthermore, with an EC50 value of 36.71 μg/mL, carvacrol demonstrated the highest inhibitory impact on Alternaria alternata among the 15 components of essential oils. In the meantime, treatment with EC50 concentration of carvacrol was found to be more effective than 0.5 EC50 concentration for controlling Alternaria alternata-induced decay disease of red grapes. The fruits exhibited remarkable improvements in the activity of defense-related enzymes, preservation of the greatest hardness and total soluble solids content, reduction in membrane lipid peroxidation in the peel, and preservation of the structural integrity of peel cells. Consequently, carvacrol was able to prevent the Alternaria alternata infestation disease that affects red grapes, and its EC50 concentration produced the greatest outcomes.

Fungicide-free management of Alternaria leaf blotch and fruit spot on apple indicates Alternaria spp. as secondary colonizer

The fungal genus Alternaria is a pan-global pathogen of > 100 crops, and is associated with the globally expanding Alternaria leaf blotch in apple (Malus x domestica Borkh.) which leads to severe leaf necrosis, premature defoliation, and large economic losses. Up to date, the epidemiology of many Alternaria species is still not resolved as they can be saprophytic, parasitic or shift between both lifestyles and are also classified as primary pathogen able to infect healthy tissue. We argue that Alternaria spp. does not act as primary pathogen, but only as a necrosis-dependent opportunist. We studied the infection biology of Alternaria spp. under controlled conditions and monitored disease prevalence in real orchards and validated our ideas by applying fungicide-free treatments in 3-years field experiments. Alternaria spp. isolates were not able to induce necroses in healthy tissue, but only when prior induced damages existed. Next, leaf-applied fertilizers, without fungicidal effect, reduced Alternaria-associated symptoms (- 72.7%, SE: ± 2.5%) with the same efficacy as fungicides. Finally, low leaf magnesium, sulphur, and manganese concentrations were consistently linked with Alternaria-associated leaf blotch. Fruit spot incidence correlated positively with leaf blotch, was also reduced by fertilizer treatments, and did not expand during storage unlike other fungus-mediated diseases. Our findings suggest that Alternaria spp. may be a consequence of leaf blotch rather than its primary cause, as it appears to colonize the physiologically induced leaf blotch. Taking into account existing observations that Alternaria infection is connected to weakened hosts, the distinction may appear slight, but is of great significance, as we can now (a) explain the mechanism of how different stresses result in colonization with Alternaria spp. and (b) substitute fungicides for a basic leaf fertilizer. Therefore, our findings can result in significant decreases in environmental costs due to reduced fungicide use, especially if the same mechanism applies to other crops.

Amylolytic and antibacterial activity of filamentous fungi isolated from the rhizosphere of different plants grown in the Tamanghasset region

In the present study, we were interested in studying the amylolytic and antibacterial activity of some filamentous fungi isolated from the rhizosphere of cultivated plants in Tamanghasset region. Consequently, 11 pure strains belonging to the different fungal genera were isolated Alternaria, Aspergillus, Cladosporium, Curvularia, Fusarium, Mucor and Penicillium. Positive result of amylolytic activity was revealed on all the isolated strains, with important hydrolysis zones of 54.33 ± 1.15 mm, 54.00 ± 3.61 mm, 52.00 ± 6.08 mm and 51.33 ± 15.01 mm for Aspergillus sp.1, Curvularia sp., Fusarium sp.2 and Mucor sp. respectively. In addition, analysis of variance (ANOVA) of the means of hydrolysis zones diameters shows that the values linked by the same letter do not show any significant difference at P < 0.05. Antibacterial activity of the isolated fungal was demonstrated by the agar cylinder technique against four pathogenic bacterial strains. The results showed a variability of the inhibition zones, thus the most important results were recorded against S. aureus, E. coli and K. pneumonia for all fungi which produced inhibition zones ranging from 15.33 ± 0.00 to 23.66 ± 1.71 mm. while all isolate had the lowest inhibition zone against P. aeruginosa. In conclusion, the obtained results indicated the isolated filamentous fungi have the potential to inhibit the four pathogenic bacterial strains, S. aureus, E. coli, K. pneumonia and P. aeruginosa, while simultaneously showed significant amylolytic activity.