Plant pathogens have agricultural impacts on a global scale and resolving the timing and route of their spread can aid crop protection and inform control strategies. However, the evolutionary and phylogeographic history of plant pathogens in Eurasia remains largely unknown because of the difficulties in sampling across such a large landmass. Here, we show that turnip mosaic potyvirus (TuMV), a significant pathogen of brassica crops, spread from west to east across Eurasia from about the 17th century CE. We used a Bayesian phylogenetic approach to analyze 579 whole genome sequences and up to 713 partial sequences of TuMV, including 122 previously unknown genome sequences from isolates that we collected over the past five decades. Our phylogeographic and molecular clock analyses showed that TuMV isolates of the Asian-Brassica/Raphanus (BR) and basal-BR groups and world-Brassica3 (B3) subgroup spread from the center of emergence to the rest of Eurasia in relation to the host plants grown in each country. The migration pathways of TuMV have retraced some of the major historical trade arteries in Eurasia, a network that formed the Silk Road, and the regional variation of the virus is partly characterized by different type patterns of recombinants. Our study presents a complex and detailed picture of the timescale and major transmission routes of an important plant pathogen.

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Although wheat streak mosaic virus (WSMV) is a well-known pathogen inducing significant crop losses and endangering wheat production worldwide, the recent discovery of High Plains wheat mosaic virus (HPWMoV) in Ukraine raises questions on the co-existence of these two viruses having a similar host range and the same mite vector. Here we report on the screening of winter wheat industrial plantings in several important regions of Ukraine for WSMV and HPWMoV. WSMV was identified in an extremely high number of symptomatic plants (>85%) as compared to HPWMoV detected in 40% of wheat samples. Importantly, the preferred mode of HPWMoV circulation in Ukraine was mixed infection with WSMV (>30%) as opposed to WSMV, which was typically found in monoinfection (60%). Screening wheat varieties for possible virus resistance indicated that all but one were susceptible to WSMV, whereas over 50% of the same varieties were not naturally infected with HPWMoV. Overall, phylogenetic analysis of the collected WSMV and HPWMoV isolates indicated their high identity and similarity to other known isolates of the respective viruses. Here we first characterize WSMV isolates found in winter wheat plants in mono- or mixed infection with HPWMoV, which was recently reported as a typical wheat pathogen in Ukraine.

Viral diseases are one of the factors governing yield of cereal crops which is a key element to guaranteeing food security in Ukraine. This work assesses spread of most harmful viruses infecting cereals in agriecosystems using different diagnostic approaches. Methods. Viruses were detected in collected samples using double-antibody sandwich enzyme-linked immunosorbent assay with commercial test systems specific to 12 cereal viruses. Transmission electron microscopy was used for direct detection of virus particles. Results. To evaluate the spread of cereal viruses, we have carried out a 15-year monitoring of cereal crops in different regions of Ukraine. For virus screening, we collected plants with typical virus-like symptoms (mosaic, leaf discoloration, etc.). We have identified arthropod-transmitted viruses: Barley yellow dwarf virus-PAV (BYDV-PAV), Barley yellow dwarf virus-MAV (BYDV-MAV), Cereal yellow dwarf virus-RPV (CYDV-RPV), Wheat streak mosaic virus (WSMV) and Wheat dwarf virus (WDV). Brome mosaic virus (BMV) and Barley stripe mosaic virus (BSMV) were sporadically detected in the commercial fields under cereals, as well as several soil-borne viruses, including Wheat spindle streak mosaic virus (WSSMV), Soil-borne cereal mosaic virus (SBCMV), Soil-borne wheat mosaic virus (SBWMV) and Barley mild mosaic virus (BaMMV). Conclusions. Barley yellow dwarf virus-PAV, Wheat streak mosaic virus and Wheat dwarf virus are the most spread viruses endangering cereals' cultivation in Ukraine. During the last 15 years, these viruses gained not only in terms of spread but also in the context of their economic effect.

The effects of low dose chronic radiation on plant disease resistance and fungal and virus infections have been studied. The results obtained in the 10-km Chernobyl zone demonstrated a decrease in plant disease resistance and appearance of a "new" population of stem rust agents of cereal with a high frequency of more virulent clones. Radionuclide contamination and heavy metals lead to wider virus spread and a higher diversity of virus species. The Chernobyl zone is a territory of enhanced risk and potential threats for the environment. A special type of monitoring of microevolution processes in plant pathogens should provide better understanding of how serious these potential threats are.