Host‐virus interaction between tobacco mild green mosaic virus strain U2 and tropical soda apple resulting in systemic hypersensitive necrosis and the host range, survival, spread, and molecular characterization of the virus

Abstract

BackgroundTobacco mild green mosaic virus strain U2 (TMGMV‐U2) is a registered active ingredient in a bioherbicide to control tropical soda apple (TSA), Solanum viarum, an invasive weed. As required for registration, we developed empirical data on the host‐virus interaction and the virus's host range, survival, spread, and genomic sequence.ResultsTMGMV‐U2 killed TSA plants by causing systemic hypersensitive necrosis (SHN). It elicited local lesions in inoculated leaves which was followed by the plant's wilting and death. It moved from inoculated terminal leaves through the vasculature to roots and then to newly developed leaves. Phloem death was implicated in wilting and plant death. The SHN response was attenuated in plants grown at constant 32 °C. TMGMV‐U2 titer in TSA was low compared to a systemically susceptible tobacco. The virus remained infective for up to 6 mo in infected dead TSA tissues and in soil in which infected plants had grown. Susceptible tobacco and pepper plants grown in soil that previously had infected dead TSA or in soil amended with the virus remained asymptomatic and virus‐free. A susceptible pepper crop grown in a field block following two consecutive crops of TMGMV‐U2‐infected susceptible tobacco grew disease‐free and virus‐free and without yield loss. Purified TMGMV‐U2 was infective for 1 yr when stored at ‐20 °C or 5 °C and for 1 mo at room temperature. No virus spread was found in the field. Genomic analyses confirmed the registered isolate to be a U2 strain and free of satellite TMV. The TMGMV‐U2‐susceptible species preponderantly belonged to the Solanaceae. A few hosts that were killed belonged to this family. Several new hosts to TMGMV‐U2 were found. These data enabled registration of TMGMV‐U2.ConclusionTMGMV‐U2 can be used safely as a bioherbicide without risks to nontarget plants and the environment.This article is protected by copyright. All rights reserved.

Use of plant viruses as bioherbicides: the first virus‐based bioherbicide and future opportunities

“…Our data indicated a 'moderately broad' host range for TMGMV-U2 (Tables 1 and 2). These data and the published host range of TMGMV confirmed that the majority of TMGMV-susceptible plants were in the Solanaceae, 22,26 and that TMGMV-U2 is undoubtedly a Solanaceae-adapted virus. 56 The SHN was expressed only in a small number of species, all in the Solanaceae.…”

“…22 In a preliminary host range study with solanaceous plants of 32 different species, TMGMV-U2 elicited host responses ranging from asymptomatic infection (ELISA-positive) to mild systemic mosaic and local lesions. More extensive host range data are presented in Charudattan et al 22 Among the susceptible species, only TSA was killed completely and in a characteristic and predictable manner as described above. Multiple greenhouse trials and two small-scale field trials in two counties of Florida confirmed the efficacy of TMGMV-U2 as a bioherbicide candidate.…”

“…29 Using a PCR probe analysis, we determined our bioherbicide isolate of TMGMV to be TMGMV-S (U2). 22 A satellite tobacco mosaic virus (STMV), a small spherical ssRNA virus, is associated with TMGMV-L (U5) from N. glauca in southern California. 30 Since satellite viruses, including STMV, can attenuate or otherwise modify the expression of the disease phenotype, at least in certain hosts, 30 we analyzed our bioherbicide isolate by using doublestranded RNA and serological reaction with anti-STMV antserum.…”

“…22 A few weeks after infection and localized HR elicitation, TMGMV-U2 spreads systemically throughout the TSA plant, including the roots, blights the phloem tissue, and causes wilting and eventual plant death (i.e., SHN). 22 The SHN is likely the result of programmed cell death and inhibition of virus multiplication. 39 The restricted or reduced virus multiplication has also been confirmed from our data.…”

“…It was addressed in a twotiered host range study. 22 Our company has conducted the most exhaustive host range study of TMGMV-U2 to date by screening 435 species-cultivars in 183 genera and 61 families, including important crop plants, native plants, weeds, and T&E species. Species in the family Solanaceae received particular emphasis.…”