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

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 ToSRVinfected 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.

Population Dynamics of Whiteflies and Associated Viruses in South America: Research Progress and Perspectives

“…It is essential to understand that these insects can migrate from a crop to another, being responsible for disease outbreaks, especially when they are close and in different development stages. Recent studies conducted in Brazil, in the State of São Paulo, noticed a 10% incidence of asymptomatic ToSRV infection in senescent soybean near to recently transplanted tomato crops in which their incidence of symptomatic ToSRV was 57-70%, supporting the hypothesis of soybean crops acting like an amplifier host for begomoviruses in tomato [167].…”

“…Tomato begomoviruses can infect not only solanaceous plant species, but also legumes such as common and lima bean and soybean. Recently, it was shown under experimental conditions that asymptomatic common bean and soybeans infected with ToSRV can be potential amplifier hosts for these viruses and vectors to a nearby tomato crop, contributing even further to the begomovirus epidemic in Brazil [167]. The ToSRV was also reported infecting common bean and soybean in central Brazil, but the incidence in both crops was lower than 3.5%, and all infected plants were asymptomatic.…”

“…The ToSRV was also reported infecting common bean and soybean in central Brazil, but the incidence in both crops was lower than 3.5%, and all infected plants were asymptomatic. However, a soybean area with >10% incidence of asymptomatic ToSRV-infected soybean plants was found in the southeast of Brazil (Sao Paulo State) in 2018 [167]. However, the impacts on bean and soybean production caused by ToSRV are unknown.…”

Indirect effect of elevated CO2 concentration on Bemisia tabaci MEAM1 feeding on Bt soybean plants

“…Certain long‐term predictions suggested an increase in plant susceptibility to B. tabaci and viruses transmitted by B. tabaci (Ramos, Kumar, Shabani, & Picanço, 2019). Furthermore, soybean is known to act as an amplifier host for begomoviruses and B. tabaci , contributing to virus epidemics in tomato crops in Brazil (Bergamin Filho et al., 2020).…”