Massive screening of natural and biological compounds to select the best candidates for biocontrol of Verticillium Wilt of Olive in the Mediterranean basin

Abstract: Verticillium wilt of olive (Olea europaea; VWO), caused by Verticillium dahliae, is the most serious biotic challenge to this crop in the Mediterranean basin. Due to the lack of a truly efficient method to control VWO, an integrated management strategy is needed to reduce both pathogen dispersal and disease incidence in olive orchards. Thus, the use of natural or biological compounds arises as a potential complementary and eco-friendly control tool against VWO. In this context, the Agroforestry Research Group AGR-216 from the University of Cordoba (Spain) has been developing an extensive research line on biocontrol of VWO since 2011, which has contributed markedly in generating knowledge on such topic towards to obtain potential biological solutions against the disease in the near future. To reach this goal, more than 250 compounds including microorganisms (fungi, bacteria), organic amendments (waste from animals and food industry), natural substances (essential oils, plant extracts), biostimulants, nutrients and resistance inductors have been tested through a massive screening under controlled conditions by i) in vitro sensitivity tests or dual cultures to evaluate their effect on mycelial growth; ii) in naturally infested soil evaluating their effect on microsclerotia viability; and iii) in planta, by the effect on the infection of olive potted plants. The most promising compounds from this screening have been also tested under natural field conditions considering representative scenarios of the different olive-growing regions of Andalusia. Based on the results already obtained, the non-pathogenic strains of F. oxysporum FO12, and the grape marc compost CGR03 have resulted among the most promising candidates, reaching around 100 % of the inhibition of the disease in both under controlled and in naturally infested soil conditions. More recently, new insights into the biological control of the disease have been obtained determining the action of plant biostimulants and microorganism as host resistance inductors. The strain Aureobasidium pullulans AP-08 produces a strong accumulation of Jasmonic acid and Jasmonic acid-isoleucine in treated olive plants, enhancing the plant immune system. Altogether, this work will be useful to select the best candidates towards the biocontrol of VWO, matching great within the frame of the European Green Deal.