In vitro evaluation of dill seed essential oil antifungal activities to control Zymoseptoria tritici.

Zymoseptoria tritici (teleomorph: Mycosphaerella graminicola) is the causal agent of Septoria Leaf Blotch of wheat (up to 40% yield loss). The study aims to evaluate the antifungal activities of dill seed Essential Oil (EO) on this pathogen to investigate an alternative solution to decrease the use of synthetic fungicides in the context of sustainable agriculture. Thus, two strains of Zymoseptoria tritici in relation to their sensitivity to DOMIs were tested in microplates (S6, sensitive strain; R1187, resistant strain). The essays were repeatedly carried out with dill seed EO crude, with Tween 80 (5% v/v) or with DMSO (1% v/v). A range of nine EO dilutions were tried out in comparison to two fungicides: a DMI (metconazole) and a SDHI (Boscalid). A Gas Chromatography - Mass Spectrometry (GC-MS) analysis reveals that dill seed EO is mostly composed of Carvone (45%) and Limonene (25%). Consequently, D-Carvone/L-Carvone and D-Limonene/L-Limonene were tested as well to determine the origins of the EO effectiveness observed. The IC50 (half maximal inhibitory concentration) are calculated and then statistically analysed to find significant differences between each product tested. The comparison of the IC50 shows that S6 is more sensitive to metconazole than R1187 but they both have the same sensitivity to Boscalid. Dill seed EO, D-Carvone/L-Carvone have the same effectiveness on S6 whatever the preparation tested. D-Limonene/L-Limonene are less efficient unless they are supplemented with Tween 80. On R1187, Dill seed EO is more efficient when it is prepared with Tween 80. This efficiency is also observed for D-Carvone/L-Carvone whatever the preparation tested. D-Limonene/L-Limonene are generally less efficient than Carvone even if L-limonene is as efficient as L-Carvone when these products are prepared with Tween 80. Dill seed EO used crude or with DMSO is more efficient on S6 (350 mg/L) than on R1187 (1000 mg/L) but with Tween 80, the EO effectiveness is the same on both strains (300 mg/L). So DMSO doesn't have any effects on both strains while Tween 80 seemsto improve the EO efficiency on the resistant strain. Carvone appears to be more efficient than Limonene, which indicates that the major compound is largely responsible for the observed EO efficiencies. In Addition, the EO preparation seems to play a role in the antifungal activities, especially on the resistant strain than the sensitive strain. The two fungicides tested are still the most efficient molecules in the control of Zymoseptoria tritici.