The spread of aggressive fungal pathogens into previously non-endemic regions is a major threat to plant health and food security. Analyses of the spatial and genetic structure of plant pathogens offer valuable insights into their origin, dispersal mechanisms and evolution, and have been useful to develop successful disease management strategies. Here, we elucidated the genetic diversity, population structure and demographic history of worldwide invasion of the ascomycete Verticillium dahliae, a soil-borne pathogen, using a global collection of 1100 isolates from multiple plant hosts and countries. Seven well-differentiated genetic clusters were revealed through discriminant analysis of principal components (DAPC), but no strong associations between these clusters and host/geographic origin of isolates were found. Analyses of clonal evolutionary relationships among multilocus genotypes with the eBURST algorithm and analyses of genetic distances revealed that genetic clusters represented several ancient evolutionary lineages with broad geographic distribution and wide host range. Comparison of different scenarios of demographic history using approximate Bayesian computations revealed the branching order among the different genetic clusters and lineages. The different lineages may represent incipient species, and this raises questions with respect to their evolutionary origin and the factors allowing their maintenance in the same areas and same hosts without evidence of admixture between them. Based on the above findings and the biology of V. dahliae, we conclude that anthropogenic movement has played an important role in spreading V. dahliae lineages. Our findings have implications for the development of management strategies such as quarantine measures and crop resistance breeding.

Field experiments were conducted in the two cropping seasons between 2002 and 2004 to determine effects on soil-borne diseases, weeds and yield of strawberry of raised bed solarization (RBS), alone or with chicken manure (CM) amendment, methyl bromide (MB), TeloDrip (1,3-dichloropropene + chloropicrin), short RBS combined with reduced doses of metam sodium (MS) and TeloDrip. In both seasons, raised bed soil solarization (for 7 weeks) alone or with CM amendment (10 t/ha), MS (50 ml/m 2 ) after 2-week RBS, and MB (50 g/m 2 ) significantly reduced soil-borne diseases (caused by Rhizoctonia spp. and Phytophthora cactorum) while application of TeloDrip at a rate of 500 kg/ha and a half-dose after short solarization controlled the soil-borne diseases to a lesser extent in the 2003-2004 cropping season. All treatments provided effective control of four weed species; annual bluegrass (Poa annua), common purslane (Portulaca oleracea), redroot pigweed (Amaranthus retroflexus) and barnyardgrass (Echinochloa crus-galli) but not horseweed (Conyza canadensis). In the first year trial, total marketable yields from RBS with or without CM and 2-week solarization plus MS were equivalent to yields produced by MB treatment whereas only raised bed soil solarization and CM amendment led to the same increase of yield as MB in the second year.

A weed survey conducted in 2004 and 2005 in Aydin province of Turkey showed that Solanum nigrum, Xanthium strumarium, Amaranthus retroflexus, Portulaca oleracea, Sonchus oleraceus and Datura stramonium were the most prevalent weeds in the cotton fields exhibiting Verticillium wilt. Verticillium dahliae Kleb. was recovered from A. retroflexus and X. strumarium in those cotton fields. This is the first report of V. dahliae occurring naturally in A. retroflexus in Turkey. Pathogenicity tests on cotton and weeds showed that the virulence of V. dahliae isolates from weeds was higher on cotton plants than on weeds, with the disease severity ranging from 31.7% to 98.0%. Disease severity of V. dahliae isolates was 54.7-93.9% on eggplant, 23.7-51.6% on cucumber and 11.0-16.4% on tomato, whereas it did not cause any disease symptoms, or only low levels, on pepper and bell pepper. Two vegetative compatibility groups (VCGs) were identified among seven tested weed isolates: VCG2A (two isolates) and VCG2B (three isolates) using international reference strains.

This study was aimed to determine the causal agents of soil-borne fungal diseases that pose a threat to the strawberry production in Aydin, Turkey and to investigate the potential effects of solarization and three fumigants (metam sodium, dazomet and methyl bromide) on these diseases. As the agents of the diseases, Rhizoctonia solani Ku¨hn. Phytophthora cactorum (Lebert and Cohn) J. Schro¨t., Verticillium dahliae Kleb. were detected. Trials to determine the effects of solarization and the fumigants were conducted in two successive cropping seasons of strawberries. Soil temperatures at 0, 10 and 20 cm depth of solarized and unsolarized plots were measured. In 1998-99, soil solarization gave significantly better control of the diseases than fumigants and the highest yield of 59 tons/ha was obtained from the solarized plots. This is followed by dazomet (50 g/m 2 ) treated plots with the yield of 34.4 tons/ha, while non-treated control plots yielded 22.4 tons/ha. In 1999-2000, all treatments gave higher yields than non-treated control plots (26.1 tons/ha), but there were no difference (P < 0.05) among the treated plots where the yields varied between 33.3 and 36.1 tons/ha.

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