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.

BACKGROUND: Tobacco 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. RESULTS: TMGMV-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 months 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 year when stored at -20 °C or 5 °C and for 1 month 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. CONCLUSION: TMGMV-U2 can be used safely as a bioherbicide without risks to nontarget plants and the environment. © 2023 Society of Chemical Industry.

Modelling distributions of Aedes aegypti and Aedes albopictus using climate, host density and interspecies competition.

Florida faces the challenge of repeated introduction and autochthonous transmission of arboviruses transmitted by Aedes aegypti and Aedes albopictus. Empirically-based predictive models of the spatial distribution of these species would aid surveillance and vector control efforts. To predict the occurrence and abundance of these species, we fit a mixed-effects zero-inflated negative binomial regression to a mosquito surveillance dataset with records from more than 200,000 trap days, representative of 53% of the land area and ranging from 2004 to 2018 in Florida. We found an asymmetrical competitive interaction between adult populations of Aedes aegypti and Aedes albopictus for the sampled sites. Wind speed was negatively associated with the occurrence and abundance of both vectors. Our model predictions show high accuracy (72.9% to 94.5%) in validation tests leaving out a random 10% subset of sites and data since 2017, suggesting a potential for predicting the distribution of the two Aedes vectors.

Evaluation of Agar and Grain Media for Mass Production of Conidia of Dactylaria higginsii.

Growth and sporulation of Dactylaria higginsii were quantified on complex agar media containing biological materials (group 1) and chemically defined agar media (group 2), as well as on grains, and the inoculum produced on these various substrates was tested for virulence on Cyperus rotundus. The fungus grew well between 25 and 30°C on potato dextrose agar (PDA), with 27°C being the optimum temperature. Generally, conidial production was highly variable and lower on complex agar media than on chemically defined media. Addition of purple nutsedge leaves to PDA did not increase colony growth or conidial production when compared with una-mended PDA. Conidial production was lowest on brown rice compared with white rice or white rice with nutsedge leaves. Peak production on grain media occurred from day 12 in test 1 (2.4 × 106 spores/g of grain) and on day 16 in test 2 (2.5 × 106 spores/g of grain). Germination rate of conidia produced on white rice was 50% compared with the near 100% germination of conidia produced on PDA or on white rice amended with potato dextrose broth (PDB). Conidia produced on white rice or PDA, when tested fresh or after two washings, were less virulent on C. rotundus than conidia from white rice amended with PDB. After four washings, conidia from all three media produced the same level of disease severity. White rice supplemented with PDB and PDA in trays were suitable for mass production of conidia of D. higginsii.