Compatibility between the endoparasitoid Hyposoter didymator and the entomopathogenic fungus Metarhizium brunneum: a laboratory simulation for the simultaneous use to control Spodoptera littoralis.

BACKGROUND: The cotton leafworm, Spodoptera littoralis, is one of the most destructive pests in the Mediterranean basin, being predominantly controlled using synthetic chemical pesticides. Strain EAMa 01/58-Su of the fungus Metarhizium brunneum and the parasitoid Hyposoter didymator are promising biological control agents for this pest. In this study, we assessed the compatibility between these two agents to control S. littoralis under joint attack scenarios. RESULTS: Firstly, the direct and indirect effects of the fungus towards parasitoid adults were studied. The fungus significantly decreased life expectancy of the parasitoid (mortality = 62.5%; mean lethal concentration = 1.85 × 106 conidia ml-1 ; average survival time = 92.2 h) when applied at high concentrations (108 conidia ml-1 ), whereas it did not affect the reproductive potential of the parasitoid females during the 3 days after treatment. Secondly, the combinations between the two agents to control S. littoralis under different simultaneous use scenarios (inoculation of S. littoralis larvae with the fungus before being exposed to parasitoid females and vice versa) were investigated, with additive effect in all cases. A significant effect on fitness (preimaginal development time and reproductive potential) of the F1 parasitoid generation were detected. Moreover, parasitization significantly reduced the total hemocytes in S. littoralis hemolymph compared with the control, promoting fungal infection. Finally, parasitoids showed a significant preference for non-inoculated S. littoralis larvae. CONCLUSIONS: We demonstrated compatibility (additive effect) between fungus and parasitoid under different joint attack scenarios to control S. littoralis in laboratory conditions. However, this will be supported by our ongoing greenhouse and field studies. © 2019 Society of Chemical Industry.

Genetics, Host Range, and Molecular and Pathogenic Characterization of Verticillium dahliae From Sunflower Reveal Two Differentiated Groups in Europe.

Verticillium wilt and leaf mottle of sunflower, caused by the fungus Verticillium dahliae (Vd) has become a major constraint to sunflower oil production in temperate European countries. Information about Vd from sunflower is very scarce despite genetics, molecular traits and pathogenic abilities of fungal strains affecting many other crops being widely known. Understanding and characterizing the diversity of Vd populations in those countries where sunflowers are frequent and severely affected by the fungus are essential for efficient breeding for resistance. In this study, we have analyzed genetic, molecular and pathogenic traits of Vd isolates affecting sunflower in European countries. When their genetics was investigated, almost all the isolates from France, Italy, Spain, Argentina, and Ukraine were assigned to vegetative compatibility group (VCG) 2B. In Bulgaria, Turkey, Romania, and Ukraine, some isolates were assigned to VCG6, but some others could not be assigned to any VCG. Genotyping markers used for Vd affecting crops other than sunflower showed that all the isolates were molecularly identified as race 2 and that markers of defoliating (D) and non-defoliating (ND) pathotypes distinguished two well-differentiated clusters, one (E) grouping those isolates from Eastern Europe and the other (W) all those from the Western Europe and Argentina. All the isolates in cluster W were VCG2B, while the isolates in cluster E belonged to an unknown VCG or to VCG6. When the host range was investigated in the greenhouse, the fungus was highly pathogenic to artichoke, showing the importance of farming alternatives in the management of Verticillium attacks. Sunflower genotypes were inoculated with a selection of isolates in two experiments. Two groups were identified, one including the isolates from Western Europe, Argentina, and Ukraine, and the other including isolates from Bulgaria, Romania, and Turkey. Three pathogenic races were differentiated: V1, V2-EE (Eastern Europe) and V2-WE (Western Europe). Similarly, three differentials are proposed for race identification: HA 458 (universal susceptible), HA 89 (resistant to V2-EE, susceptible to V2-WE) and INRA2603 (susceptible to V2-EE, resistant to V2-WE). The diversity found in Vd affecting sunflower must be taken into account in the search for resistance to the pathogen for European environments of sunflower production.