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.

Rice sheath and stem diseases caused by Rhizoctonia and Sclerotium species are problems in rice growing regions of Southeast Asia. In the summer season of 2007, in rice fields of Pyinmana Township in Myanmar, rice stems were visually observed with brownish to black lesions without distinct margins. The causal pathogen was isolated by placing 1 cm diseased stems on 2% water agar media and incubating at 28 ° C for seven days. The hyphae of the non-sporulating culture was stained with a mixture of safranine solution and 3% KOH (Bandoni, 1979). The hyphal width was measured to be within a range of 6 to 10 μ m and binucleate hyphae were observed between the septa. Small, globose and reddish brown to black coloured mature sclerotia measuring 0·24-0·43 mm were observed in culture. Based upon these characteristics, the fungus was initially identified as Sclerotium hydrophilum . On comparing the rDNA-ITS sequences of the isolate (GenBank Accession No. FJ595944) with that of a S. hydrophilum reference (DQ875597) there was found to be 99% identity.To confirm pathogenicity, ten rice sheath tissues were inoculated by placing a five day-old mycelial plug on the stem 1 cm below the axil of the fully mature leaf and wrapping with parafilm. Control plants were treated in the same manner using a plug of 2% water agar. After five days, symptoms on all inoculated plants were similar to those occurring in nature.Control plants did not develop symptoms. The fungus was re-isolated from inoculated plants, confirming Koch's postulates.Stem rot of rice caused by S. hydrophilum has been reported previously in other rice growing countries in Southeast Asia (Kimiharu et al ., 2004), but this is the first report of this pathogen on rice from Myanmar. Further surveys and isolate collection will be needed to evaluate its geographic distribution and prevalence in Myanmar.

No abstract

No abstract

No abstract