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Soil solarization, either singly or in combination with a reduced dosage (34 g/m2) of methyl bromide, was effective in controlling verticillium wilt of globe artichokes for three successive cropping seasons. Both treatments resulted in greatly reduced natural populations of Verticillium dahliae microsclerotia, which were positively correlated with significant reductions in diseased plants as well as with the early formation of primary artichoke heads and increased yield. Propagules of Talaromyces flavus increased and survived better in solarized than in solarized and fumigated soils and could be partially involved in the effectiveness of solarization. Propagules of Aspergillus terreus invariably increased in treated plots but their involvement in the longevity of the treatment is questionable.

SPIROU Co., 5 Marconi Str., 142 22 Athens (Greece)Seedlings of tomato (19) and cucurbits (33), previously selected as rootstocks for commercial cultivars, were evaluated for their resistance to verticillium wilt under glasshouse conditions. Disease scoring was based on foliar symptoms, but in plants with no visual or ambiguous symptoms the presence of the pathogen was confirmed by isolations or PCR using specific DNA primers. Five of the cucurbit rootstocks showed resistance to infection, 11 were moderately infected, 11 were susceptible, while the remaining six were very susceptible. In general, Cucurbita pep0 (courgette, pumpkin) and Lagenaria siceraria tolerated infection, Cucumis melo rootstocks were susceptible and Citrullus vulgaris was the most susceptible. When inoculated with race 1 of the pathogen, one of the tomato rootstocks was very resistant, three moderately resistant, nine tolerant, ten susceptible and one very susceptible. Pathogenicity tests with race 2 showed that none of the rootstocks exhibited high tolerance, but that there was some variation in susceptibility. Research is under way to evaluate the reaction of commercial cultivars to verticilliurn wilt when grafted onto resistant rootstocks.

In a comparison of different methods for estimatingVerticillium dahliae in soil, 14 soil samples were analyzed in a blinded fashion by 13 research groups in seven countries, using their preferred methods. One group analyzed only four samples. Twelve soil samples were naturally infested, and two had known numbers of microsclerotia of V. dahliae added to them. In addition, a control was included to determine whether transport had an effect on the results. Results differed considerably among the research groups. There was a 118-fold difference between the groups with the lowest and highest mean estimates. Results of the other groups were evenly distributed between these extremes. In general, methods based on plating dry soil samples gave higher numbers of V. dahliae than did plating of an aqueous soil suspension. Recovery of V. dahliae from samples with added microsclerotia varied from 0 to 59%. Most of the variability within each analysis was at the petri dish level. The results indicate the necessity to check the performance of detection assays regularly by comparing recoveries with other laboratories, using a common set of soil samples. We conclude that wet plating assays are less accurate than dry plating assays.

The soilborne fungi Sclerotinia sclerotiorum, Rhizoctonia solani and the oomycete Pythium ultimum are among the most destructive pathogens for lettuce production. The application of the biocontrol agent Paenibacillus alvei K165 to the transplant soil plug of lettuce resulted in reduced S. sclerotiorum, R. solani and P. ultimum foliar symptoms and incidence compared to untreated controls, despite the suppressive effect of the pathogens on the rhizosphere population of K165. In vitro, K165 inhibited the growth of S. sclerotiorum and R. solani but not P. ultimum. Furthermore, the expression of the pathogenesis‐related (PR) gene PR1, a marker gene of salicylic acid (SA)‐dependent plant defence, and of the Lipoxygenase (LOX) and Ethylene response factor 1 (ERF1) genes, markers of ethylene/jasmonate (ET/JA)‐dependent plant defence was recorded. K165‐treated plants challenged with P. ultimum showed up‐regulation of PR1, whereas challenge with R. solani resulted in up‐regulation of LOX and ERF1, and challenge with S. sclerotiorum resulted in up‐regulation of PR1, LOX and ERF1. This suggests that K165 triggers the SA‐ and the ET/JA‐mediated induced systemic resistance against P. ultimum and R. solani, respectively, while the simultaneous activation of the SA and ET/JA signalling pathways is proposed for S. sclerotiorum.

Cotton (Gossypium hirsutum) wilt caused by Fusarium oxysporum f. sp. vasinfectum (Fov) is considered as a major threat for commercial cotton production worldwide. Relative expression ratios of two key pathogenesis-related (PR) genes (PR-3 and PR-10) and a detoxification gene (GST18) were compared between a fully susceptible ("LACTA") and a partially field-resistant ("EMERALD") cultivar after challenging with an Australian Fov isolate, as well as after pre-treatments with chemical inducers of defense such as BION® (a chemical analog of salicylic acid) and methyl-jasmonate (MeJA) prior to Fov inoculation. It was demonstrated that in both hypocotyls and roots of "EMERALD", all PR genes were over-expressed after inoculation with Fov but not in the fully susceptible cultivar. Fov inoculation did not significantly affect GST18 expression in both cultivars. Exogenous application of each defense elicitor, prior to Fov inoculation, resulted in up-regulation of the three genes in root tissues of the fully susceptible cultivar. BION® application did not influence PR-3 expression in hypocotyls of both cultivars, whereas MeJA application resulted in induction of PR-3 in both cultivars. Furthermore, in hypocotyls of "LACTA", over-expression of PR-10 was recorded after treatment with each chemical inducer. This pathogen exhibited different ability in eliciting oxidative burst in roots of the two cotton cultivars used in our analysis.

Talaromyces flavus, a fungal antagonist of Verticillium dahliae, naturally occurring in clay loam artichoke fields or sandy loam olive groves, is able to survive following application of soil solarization. Survival was almost always linked to an increase in T. flavus populations detected in the rhizosphere of artichoke plants or olive trees with a verticillium wilt history as compared with the untreated control soils. It was evident that soil solarization resulted in the control of the disease in artichoke fields and the recovery of olive trees from V. dahliae infection. It was furthermore proved that solarization had a beneficial long‐term effect in controlling V. dahliae for a period of 2 or 3 consecutive years. This could at least partially be attributed to the activity of T. flavus in inhibiting the germination of microsclerotia or causing their death. Aspergillus terreus, another potential V. dahliae antagonist, was also found to survive and occasionally increase following the application of the technique.