Temporal and spatial progress of the diseases caused by the crinivirus tomato chlorosis virus and the begomovirus tomato severe rugose virus in tomatoes in Brazil

Efficient management of whitefly-borne diseases remains a challenge due to the lack of a comprehensive understanding of their epidemiology, particularly of the diseases tomato golden mosaic and tomato yellowing. Here, by monitoring 16 plots in four commercial fields, the temporal and spatial distribution of these two diseases were studied in tomato fields in Brazil. In the experimental plots these diseases were caused by tomato severe rugose virus (ToSRV) and tomato chlorosis virus (ToCV), respectively. The incidence of each virus was similar in the plots within a field but varied greatly among fields. Plants with symptoms for both diseases were randomly distributed in three of four spatial analyses. The curves representing the progress of both diseases were similar and contained small fluctuations, indicating that the spread of both viruses was similar under field conditions. In transmission experiments of ToSRV and ToCV by Bemisia tabaci MEAM1 (former biotype B), these viruses had a similar transmission rate in single or mixed infections. It was then shown that primary and secondary spread of ToCV were not efficiently controlled by insecticide applications. Finally, in a typical monomolecular model of disease progress, simulation of the primary dissemination of ToSRV and ToCV showed that infected plants were predominantly randomly distributed. It is concluded that, although the manner of vector transmission differs between ToSRV (persistent) and ToCV (semipersistent), the main dispersal mechanisms are most probably similar for these two diseases: primary spread is the predominant mechanism, and epidemics of these diseases have been caused by several influxes of viruliferous whiteflies.     

Influence of temperature,humidity duration and growth stage on the infection and mycotoxin production by Fusarium langsethiae and Fusarium poae in oats

High occurrence of Fusarium poae (FP) and Fusarium langsethiae (FL) and their mycotoxins nivalenol (NIV) and T-2/HT-2 have been observed in Swiss oats. Early prediction of mycotoxin levels is important for farmers and the cereal industry to minimize the risk of contaminated food and feed. Therefore, climate chamber experiments were conducted to investigate the influence of different temperatures (10, 15, 20 °C) and durations (4, 8, 12 h) at 99% relative humidity (RH) on the infection of oats with FP and FL. In addition, to discover the most susceptible period of oats, artificial FL inoculations were conducted at different growth stages. Field experiments were performed to observe the dispersal of these fungal species within the field and to investigate the weather conditions that influence the dispersal. The climate chamber experiments revealed higher contamination with NIV and T-2/HT-2 in the 10 °C treatments and with a prolonged humidity duration of 12 h 99% RH. Inoculations of oat plants at early (DC 61) and mid (DC 65) anthesis, led to higher FL infection and T-2/HT-2 accumulation in the grains compared with treatments at earlier growth stages, which might be due to an increased susceptibility during anthesis. No indication for spore dispersal was observed in the field experiments. The results obtained, together with the cropping factors that influence infection and mycotoxin production, could be used as a first step in developing forecasting models to predict the contamination of oats with the mycotoxins NIV and T-2/HT-2.     

Tomato brown rugose fruit disease: current distribution,knowledge and future prospects

Tomato is the most economically important fruit/vegetable crop grown worldwide. However, viral diseases remain an important factor limiting its productivity, with estimated quantitative and qualitative yield losses in tomato crops often reaching up to 100%. Many viruses infecting tomato have been reported, while new viral diseases have also emerged. The climatic changes the world is experiencing can be a contributing factor to the successful spread of newly emerging viruses, as well as the establishment of disease in areas that were previously either unfavourable or where the disease was absent. Because antiviral products are not available, strategies to mitigate viral diseases rely on genetic resistance/tolerance to infection, control of vectors, improvement in crop hygiene, roguing of infected plants and seed certification. Tomato brown rugose fruit virus (ToBRFV) is an emerging viral threat to tomato productivity and is currently spreading into new areas, which is of great concern to the growing global production in the absence of mitigation measures. This review presents the current knowledge about ToBRFV and future prospects for an improved understanding of the virus, which will be needed to support effective control and mitigation of the impact it is likely to cause.     

Survey on Bactrocera spp. (Tephritidae,Diptera) in Austria

Fruit fly species (Diptera: Tephritidae) of the genus Bactrocera are among the most serious orchard pests worldwide but are not native to Austria. The unexpected finding of one Bactrocera zonata adult in Vienna in 2011 initiated increasing survey efforts in Austria since 2012. Traps with male attracting lures were employed at several sites during the fruiting periods and catches were analysed. At sites in Vienna (urban area) Bactrocera specimens were trapped between 2012 and 2018, whereas no Bactrocera specimens were caught in agricultural areas or commercial orchards outside the city. Twelve specimens were identified as B. zonata and nine specimens as B. dorsalis sensu lato, though for the latter it was not possible to distinguish between B. dorsalis s.l. and B. carambolae using molecular analysis (ITS1). Molecular sequencing showed that the specimens caught were genetically different (with only a few exceptions), indicating genetically different origins. It is evident that the repeated findings of Bactrocera specimens in Vienna, where winter temperatures do not allow the establishment of tropical fruit flies, are linked to repeated entries of juveniles with infested fruits (in luggage or consignments). The results of our study reveal the need to strengthen phytosanitary import requirements for fruit commodities and travellers’ luggage in order to protect fruit production in Austria and probably in other countries.     

Temporal disease dynamics and relative importance of sexual and asexual reproduction of grape downy mildew (Plasmopara viticola) in an isolated vineyard in the North Georgia Mountains,USA

The North Georgia Mountains are the southernmost region along the United States East Coast where European wine grapes (Vitis vinifera) are grown commercially. Epidemics of downy mildew, caused by Plasmopara viticola, are frequent and severe, but little is known about the epidemiology and population biology of the pathogen in this region. Disease monitoring in an experimental vineyard from 2015 to 2017 indicated that times of disease onset and progress rates were highly variable across years and cultivars. Oospores were observed microscopically, and simulation with a process-based model indicated presence of conditions favourable for oospore germination in the spring and early summer each year. A total of 409 P. viticola isolates collected over three  years were genotyped with seven microsatellite markers, revealing very high genotypic diversity, which when combined with the observation of oospores is indicative of a sexually reproducing population. Among the 409 isolates, 225 multilocus genotypes (MLGs) were identified, of which 164 were detected only once and 61 were repeated (clonal). Eight MLGs (represented by 28 isolates) were detected across years, suggesting the possibility of asexual overwintering of P. viticola in this region. Across sampling dates, the percentage of isolates belonging to nonrepeated (unique) MLGs ranged from 27.3% to 63.2%. Even towards the end of the annual epidemic, the percentage of isolates in nonrepeated MLGs was still relatively high, around 30%. These MLGs may have originated from oospores germinating late during the growing season, although incomplete sampling at earlier dates and contribution by immigration cannot be fully excluded.     

Projecting the suitability of global and local habitats for myrtle rust (Austropuccinia psidii) using model consensus

Myrtle rust (caused by Austropuccinia psidii) affects more than 500 known host species in the Myrtaceae family. Three different modelling approaches (CLIMEX, MaxEnt and Multi-Model Framework) were used to project the habitat suitability for myrtle rust at both global and local scales. Current data on the global occurrence of myrtle rust were collected from online literature and expert solicitation. Long-term averages of climate data (1960–1990) were sourced from WorldClim and CliMond websites. Recent reports of myrtle rust in New Zealand were used for validation of model outputs but not in model training and testing. The model outputs were combined into a consensus model to identify localities projected to be suitable for myrtle rust according to two or three models (hotspots). In addition to the locations where the pathogen is currently present, all models successfully projected independent occurrence data in New Zealand suitable for establishment of the pathogen. Climate suitability for the pathogen was primarily related to temperature followed by rainfall in MaxEnt and the CLIMEX model. The results confirmed the optimum temperature range of this pathogen in the literature (15–25 °C). Additional analysis of the precipitation variables indicated that excessive rain (more than 2000 mm in warmest quarter of the year) combined with high temperatures (>30 °C) constrain pathogen establishment. The results of the current study can be useful for countries such as New Zealand, China, South Africa and Singapore where the pathogen has not fully spread or established.     

The interaction between temperature and dose on the efficacy and biochemical response of Atlantic salmon to hydrogen peroxide treatment for amoebic gill disease

Hydrogen peroxide (H₂O₂) is a commonly used treatment for a range of parasitic diseases of marine finfish, including amoebic gill disease (AGD). While this treatment is partially effective at reducing parasite load, H₂O₂ can have detrimental effects on the host under certain conditions. Treatment temperature and dose concentration are two factors that are known to influence the toxicity of H₂O₂; however, their impact on the outcome of AGD treatment remains unclear. Here, we investigated the effects of treatment temperature (8, 12 or 16°C) and dose concentration (750, 1,000, 1,250 mg/L) on the efficacy of H₂O₂ to treat AGD. We demonstrated that a 20-min bath treatment of H₂O₂ at all doses reduced both parasite load and gross gill score significantly. Parasite load and gross gill score were lowest in the 1,000 mg/L treatment performed at 12°C. At the high dose and temperature combinations, H₂O₂ caused moderate gill damage and a significant increase in the plasma concentration of electrolytes (sodium, chloride and potassium). Taken together, our study demonstrates that higher H₂O₂ treatment temperatures can adversely affect the host and do not improve the effectiveness of the treatment.     

The nature and consequences of co-infections in tilapia: A review

Co-infections commonly arise when two or multiple different pathogens infect the same host, either as simultaneous or as secondary concurrent infection. This potentiates their pathogenic effects and leads to serious negative consequences on the exposed host. Numerous studies on the occurrence of the bacterial, parasitic, fungal and viral co-infections were conducted in various tilapia species. Co-infections have been associated with serious negative impacts on susceptible fish because they increase the fish susceptibility to diseases and the likelihood of outbreaks in the affected fish. Co-infections can alter the disease course and increase the severity of disease through synergistic and, more rarely, antagonistic interactions. In this review, reports on the synergistic co-infections and their impacts on the affected tilapia species are highlighted. Additionally, their pathogenic mechanisms are briefly discussed. Tilapia producers should be aware of the possible occurrence of co-infections and their effects on the affected tilapia species and in particular of the clinical signs and course of the disease. To date, there is still limited information regarding the pathogenicity mechanisms and pathogen interactions during these co-infections. This is generally due to low awareness regarding co-infections, and in many cases, a dominant pathogen is perceived to be of vital importance and hence becomes the target of treatment while the treatment of the co-infectious agents is neglected. This review article aimed at raising awareness regarding co-infections and helping researchers and fish health specialists pay greater attention to these natural cases, leading to increased research and more consistent diagnosis of co-infectious outbreaks in order to improve control strategies to protect tilapia when infected with multiple pathogens.     

Two-year surveillance of tilapia lake virus (TiLV) reveals its wide circulation in tilapia farms and hatcheries from multiple districts of Bangladesh

Tilapia lake virus (TiLV) is an emerging pathogen in aquaculture, reportedly affecting farmed tilapia in 16 countries across multiple continents. Following an early warning in 2017 that TiLV might be widespread, we executed a surveillance programme on tilapia grow-out farms and hatcheries from 10 districts of Bangladesh in 2017 and 2019. Among farms experiencing unusual mortality, eight out of 11 farms tested positive for TiLV in 2017, and two out of seven tested positive in 2019. Investigation of asymptomatic broodstock collected from 16 tilapia hatcheries revealed that six hatcheries tested positive for TiLV. Representative samples subjected to histopathology confirmed pathognomonic lesions of syncytial hepatitis. We recovered three complete genomes of TiLV from infected fish, one from 2017 and two from 2019. Phylogenetic analyses based on both the concatenated coding sequences of 10 segments and only segment 1 consistently revealed that Bangladeshi TiLV isolates formed a unique cluster within Thai clade, suggesting a close genetic relation. In summary, this study revealed the circulation of TiLV in 10 farms and six hatcheries located in eight districts of Bangladesh. We recommend continuing TiLV-targeted surveillance efforts to identify contaminated sources to minimize the countrywide spread and severity of TiLV infection.