Amplifier Hosts May Play an Essential Role in Tomato Begomovirus Epidemics in Brazil.

Armando Bergamin Filho,de Felipe F. Oliveira,Gabriel M. Favara,Jorge A. M. Rezende,Mônica A. Macedo,Daiana Bampi

doi:10.3389/fpls.2020.00414

Abstract

Current control of tomato golden mosaic disease, caused in Brazil predominantly by tomato severe rugose virus (ToSRV), is dependent on both, planting resistant/tolerant hybrids and intensive insecticide sprays (two to three per week) for controlling Bemisia tabaci, the vector of ToSRV. Resistant hybrids only confer moderate resistance to infection by ToSRV and some tolerance to the disease. Insecticide sprays, although widely used, have failed in most tomato production areas in Brazil, as they are unable to reduce primary spread, i.e., infection caused by the influx of viruliferous whiteflies coming from external sources of inoculum. Severe epidemics are recurrently observed in some tomato fields in several Brazilian regions, which prompted us to postulate the existence in the agroecosystem, in some places and time, of amplifier hosts that provide the necessary force of infection for epidemics to occur, even in the absence of secondary spread in the target crop. Amplifier hosts are ideally asymptomatic, occur in high density near the target crop, and support growth of both virus and vector. Soybean and common bean are potential amplifier hosts for begomovirus in tomato crops. Our results support the hypothesis that soybean plants may play an important role as an amplifier host of ToSRV for tomato crops in the field, although this does not seem to be a frequent phenomenon. Successful amplification will depend on several factors, including the soybean cultivar, the soybean stage of development at the moment of infection, the ToSRV isolate, and the perfect synchrony between the beginning of a soybean field and the end of a ToSRV-infected crop, and, later, between the senescence of the ToSRV-infected soybean plants and the new tomato crop. The concept of amplifier hosts has been widely used in ecology of zoonoses but, to our knowledge, has never been used in botanical epidemiology.

Highlights

Tomatoes are one of the most important vegetable crops in Brazil and worldwide
As for processing tomatoes, high incidences of tomato severe rugose virus (ToSRV) in fresh market tomatoes are observed annually in some tomato fields in Brazil. These recurrent and localized abrupt high incidences of ToSRV prompted us to propose a hypothesis for such epidemics: the existence in the agroecosystem, in some places and time, of amplifier hosts that provide the necessary force of infection for epidemics to occur, even in the absence of secondary spread in the target crop
The amplifier-host hypothesis (Figure 1) helps to explain the recurrent rapid epidemics that occur in Brazilian conditions, despite both the weak reservoir force of infection and the prevention of secondary spread by insecticide sprays for vector control

Summary

Introduction

Tomatoes are one of the most important vegetable crops in Brazil and worldwide. In 2018, approximately 59.7 thousand hectares were planted to tomatoes in the country, and 4.1 million tons of fruit was produced (Instituto Brasileiro de Geografia e Estatística [IBGE], 2018). In Brazilian conditions, we have strong evidence that the incidence of ToSRV in populations of weed plants (reservoir) is very low (Macedo et al, 2017c; Rezende, unpublished data), and secondary spread is prevented by intensive and effective insecticide sprays for vector control. The amplifier-host hypothesis (Figure 1) helps to explain the recurrent rapid epidemics that occur in Brazilian conditions, despite both the weak reservoir force of infection and the prevention of secondary spread by insecticide sprays for vector control.

Results

Conclusion