Olive wilt is a disease caused by the fungus Verticillium dahliae, leading to the withering and death of olive trees. This pathogen survives in the soil, where it infects the roots of its host plants, which, during their growth, secrete substances, called exudates, that influence the microorganisms around them. In the case of olive trees, exudates from their roots stimulate the germination of resistance structures (called microsclerotia) to Verticillium dahliae. Under unfavorable conditions, these structures allow the fungus to survive and infect the tree. Consequently, it is through the roots of olive trees that they are infected and verticillium spreads. Although the scientific literature had already suggested that exudates were related to the infection of Verticillium dahliae, no method had been developed to prove this. Now, a research team at the María de Maeztu Unit of Excellence (Department of Agronomy of the University of Córdoba, DAUCO) has developed, for the first time, an effective method of in vitro analysis in which they have shown how the exudates of olive roots induce the germination of the fungus's microsclerotia, thus being involved in the infection and development of verticillium.
In addition to demonstrating this effect, the research team, formed by Ana López Moral, Antonio Rafael Sánchez Rodríguez, Antonio Trapero and Carlos Agustí Brisach, also studied how both the olive variety (genotype) and certain biocontrol treatments influence the effect of exudates on Verticillium dahliae.
First, they extracted exudates from three olive varieties, ranging from the most resistant to the disease (Frantoio) to the most susceptible (Picual, which is also the most common variety), and also a variety of intermediate susceptibility (Arbequina), finding that the exudates of the most resistant one, Frantoio, did not significantly induce the germination of the fungus's microsclerotia, while the exudates of the most susceptible varieties did.
Second, they looked at how biological control agents applied to different olive varieties could alter the exudates' function. They observed that in the Frantoio variety the exudates of treated plants did not induce or significantly reduce the germination of the resistance structures to the pathogen, while the exudates of treated Picual and Arbequina trees significantly reduced the viability of these structures. Thus, the results suggest that biocontrol agents can modulate the effect of exudates, decreasing the pathogen's infective capacity in susceptible varieties.
The study, published in the journal Plant and Soil, takes a further step in the study of olive wilt and the processes involved in the disease's spread. "The best way to implement rational control measures against crop pathogens is to thoroughly understand the mechanisms involved. This study is an attempt to learn about those," concluded Trapero.
Source:
Ana López-Moral, Antonio Rafael Sánchez-Rodríguez, Antonio Trapero and Carlos Agustí-Brisach, "Establishment of a method to collect root exudates from olive plants and its validation by determining the effect of root exudates against Verticillium dahliae", Plant and Soil (2022), https://doi.org/10.1007/s11104-022-05770-1.