Exploring the Risks Associated with Tomato Viruses in Belgian Diversified Production Systems and Biological Characterization of Physostegia Chlorotic Mottle Virus

• Main Author: Temple-Boyer-Dury, Coline
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2023
• Subjects: Agronomy; Botany; Cultivars; Flowers & plants; Fruits; Tomatoes; Virology; Viruses
• ISBN: 9798384151036

Sustainable control of plant diseases is one of the challenges facing agriculture currently. Therefore, it is crucial to understand pathogens in their agroecosystems. Plant viruses represent major pathogens infecting tomato, which is one of the most economically important vegetable worldwide. The impact of virus infection on plants depends on the context, anthropogenic factors and environmental conditions. The constant evolution of viruses through mutations, reassortment or recombination results in the emergence diseases that can potentially threaten crop productivity.Given the need to improve the sustainability of agriculture, diversified alternative sustainable production systems growing vegetables on soil mainly dedicated to fresh local markets have become more popular in the last decade in industrialized countries such as Belgium, France, or Canada.This thesis aims to assess and measure the issues associated with tomato viral diseases in diversified Belgian production systems.First, to achieve this objective, a complementary approach involving socio-economy and plant epidemiology was set up to obtain a more holistic vision of the situation. More specifically, we investigated the tomato virome in 21 diversified vegetable farms, in association with examining the producers' perception, the characteristics of their production systems, and observation of viral-like symptoms in the field. During this survey, one emergent rhabdovirus, physostegia chlorotic mottle virus (PhCMoV), was identified as potential viral threat. This virus was indeed associated with strong symptoms on tomato fruits and in some cases, with a high prevalence in the field. At that time, this virus was only known to infect Physostegiaand tomato in Austria and Germany and lacked biological information. PhCMoV was associated with the presence of symptoms on tomato fruits.Thus, the second approach conducted in this thesis to better understand issues related to tomato viral diseases in diversified production systems was to focus on the biological characterization of PhCMoV.In parallel, informal exchanges with other plant virologists from various research laboratories that simultaneously detected PhCMoV in several European countries and host plants reinforced the interest to focus on its characterization. Thanks to an international collaboration, the research findings of these other research groups on PhCMoV were compiled to gain a comprehensive understanding of the virus’ characteristics and associated risks. It enabled to start its characterization regarding its host range, geographical distribution, symptoms causality and genetic diversity. This successful collaboration reports the identification of PhCMoV in nine plant species across seven families and in eight additional European countries. The virus was confirmed to cause severe fruit symptoms on economically important crops such as tomato, eggplant, and cucumber. Phylogenetic analysis showed low genomic variation between samples collected 17 years apart in a same site on two different annual host plants, suggesting strong selection pressure within a specific ecosystem upon time.Thereafter, other aspects of the virus biology remained to be analyzed, such as transmission mode, incidence and disease severity. A new consortium was created with some research groups already involved in the previous study and new ones, including specialists in entomology and plant virus ecology. In total, eight partners were involved in this second study and experiments were carried out to complete the biological characterization. The natural presence of the disease in multiple sites around our laboratory and the cooperation with the growers were great advantages to study the biology of PhCMoV in its ecosystem. The host range of the virus was expanded to 20 new host plant species, its leafhopper vector (Anaceratagalliasp.) was identified, and the observed PhCMoV prevalence in Belgium suggested that the virus is widely spread in the environment. Bioassays in control conditions demonstrated that yield losses can be up to almost 100% if plants are infected at an early stage, while the severity of symptoms decreased with late infection time. The symptoms associated with the virus were also investigated in control conditions on multiple plant species.