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2.2. Fatty Acid Composition

The main fatty acids in olive oil are oleic (18:1), linoleic (18:2), palmitic (16:0), and stearic acid (18:0). The fatty acid composition is a quality parameter and an authenticity indicator of virgin olive oils []. As shown in , oleic acid displayed the highest content that ranged between 76.60% (Koroneiki from Lesvos) and 71.92% (Kolovi from Lesvos). Linoleic acid ranged between 11.63% (Kolovi from Lesvos) and 5.71% (Koroneiki from Chania), while the corresponding values for palmitic acid ranged between 13.61% (Koroneiki from Chania) and 9.65% (Kolovi from Lesvos). The stearic acid content ranged between 2.76% (Koroneiki from Chania) and 2.20% (Kolovi from Lesvos). The fatty acids, such as palmitoleic (16:1), linolenic (18:3), arachidic (20:0), gadoleic (20:1), and behenic (22:0) acid, were detected in smaller amounts (<0.9%). The content of myristic (14:0), margaric (17:0), heptadecenoic (17:1), and lignoceric (24:0) acid did not exceed 0.1%.

2.3. Classification of EVOOs According to Cultivar

It is evident (a) that samples produced from the Koroneiki cultivar form a distinct group (green area), which is clearly separated from that of Kolovi (red area). The two Koroneiki samples that lie outside the confidence eclipse originated from Lesvos. The two principal components explain 67.7% of the total variance. Examining the loading plot (b), samples from the Kolovi cultivar are positively correlated with the content of γ-tocopherol as well as linoleic (18:2), linolenic (18:3), and gadoleic (20:1) acid. The remaining fatty acids (16:0, 16:1, 18:0, 18:1, 20:0, and 22:0) and squalene correlated positively with the Koroneiki EVOOs. When student’s t-test was applied, it turned out that all variables were statistically significant (p < 0.05) between the two cultivars except from α-tocopherol, implying that its content is not dependent on variety.

2.3. Classification of EVOOs According to Cultivar

The results can be better visualized using a heatmap (). γ-Tocopherol, 20:1, 18:2, and 18:3 are present at higher levels in samples from the Kolovi cultivar and lower in the Koroneiki cultivar. The rest of the components display the opposite pattern, except for α-tocopherol, which does not show a specific pattern between the two cultivars.

4.1. Olive Oil Samples

A total of 68 monovarietal EVOOs were obtained during the harvesting period of 2018–2019 (). They were produced from two cultivars (Kolovi and Koroneiki) in three different geographical regions of Greece (Crete island, Lesvos island, and Peloponnese). The samples were packaged in dark-brown glass bottles and stored at 4 °C until analysis.

Abstract

Root-knot nematodes (RKNs) are a vital pest that causes significant yield losses and economic damage to potato plants. The use of chemical pesticides to control these nematodes has led to environmental concerns and the development of resistance in the nematode populations. Endophytic fungi offer an eco-friendly alternative to control these pests and produce secondary metabolites that have nematicidal activity against RKNs. The objective of this study is to assess the efficacy of Aspergillus flavus (), an entophyte fungus isolated from Trigonella foenum-graecum seeds, against Meloidogyne incognita in filtered culture broth using GC–MS analysis. Among them, various nematicidal secondary metabolites were produced: Gadoleic acid, Oleic acid di-ethanolamide, Oleic acid, and Palmitic acid. In addition, biochemical compounds such as Gallic acid, Catechin, Protocatechuic acid, Esculatin, Vanillic acid, Pyrocatechol, Coumarine, Cinnamic acid, 4, 3-indol butyl acetic acid and Naphthyl acetic acid by HPLC. The fungus was identified through morphological and molecular analysis, including ITS 1–4 regions of ribosomal DNA. In vitro experiments showed that culture filtrate of A. flavus had a variable effect on reducing the number of egg hatchings and larval mortality, with higher concentrations showing greater efficacy than Abamectin. The fungus inhibited the development and multiplication of M. incognita in potato plants, reducing the number of galls and eggs by 90% and 89%, respectively. A. flavus increased the activity of defense-related enzymes Chitinas, Catalyse, and Peroxidase after 15, 45, and 60 days. Leaching of the concentrated culture significantly reduced the second juveniles’ stage to 97% /250 g soil and decreased the penetration of nematodes into the roots. A. flavus cultural filtrates via soil spraying improved seedling growth and reduced nematode propagation, resulting in systemic resistance to nematode infection. Therefore, A. flavus can be an effective biological control agent for root-knot nematodes in potato plants. This approach provides a sustainable solution for farmers and minimizes the environmental impact.