Detection of <Emphasis Type="Italic">Phoma valerianellae</Emphasis> in lamb’s lettuce seeds

After the reappearance in Italy of a foliar disease of lamb’s lettuce (Valerianella olitoria L. Poll. syn. V. locusta L. Betcke) incited by Phoma valerianellae, we set out to measure the level of seed infection by this fungus, using a plating test, and to develop a molecular method for quick and reliable detection of the pathogen in seeds. All six samples of lamb’s lettuce seed tested were contaminated by P. valerianellae at levels of 0.6% to 15%. Surface disinfection of seeds did not eliminate the contamination and only reduced it to between 0.1% and 10%. The need for a sensitive, reliable and rapid diagnostic method for early identification of the fungus exists. We have developed a PCR-based method to identify the fungus in seeds. Variation within the internal transcribed spacer (ITS1, 5.8S sequences and ITS2) region of the rDNA (ITS) was used to characterize the P. valerianellae strains and to design specific primers within the ITS region.     

Efficacy of the biocontrol agents Bacillus subtilis and Ampelomyces quisqualis applied in combination with fungicides against powdery mildew of zucchini

Journal of Plant Diseases and Protection - The activity of two biofungicides based on Bacillus subtilis and Ampelomyces quisqualis alone and in combination with fungicides against Podosphaera...     

Seed transmission of<Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f.sp.<Emphasis Type="Italic">lactucae</Emphasis>

Twenty-seven seed samples belonging to the lettuce cultivars most frequently grown in Lombardy (northwestern Italy), in an area severely affected by Fusarium wilt of lettuce, were assayed for the presence ofFusarium oxysporum on a Fusarium-selective medium. Isolations were carried out on subsamples of seeds (500 to 1500) belonging to the same seed lots used for sowing, and either unwashed or disinfected in 1% sodium hypochloride. The pathogenicity of the isolates ofF. oxysporum obtained was tested in four trials carried out on lettuce cultivars of the butterhead type, very susceptible to Fusarium wilt. Nine of the 27 samples of seeds obtained from commercial seed lots used for sowing in fields affected by Fusarium wilt were contaminated byF. oxysporum. Among the 16 isolates ofF. oxysporum obtained, only one was isolated from disinfected seeds. Three of the isolates were pathogenic on the tested cultivars of lettuce, exhibiting a level of pathogenicity similar to that of the isolates ofF. oxysporum f.sp.lactucae obtained from infected wilted plants in Italy, USA and Taiwan, used as comparison. The results obtained indicate that lettuce seeds are a potential source of inoculum for Fusarium wilt of lettuce. The possibility of isolatingF. oxysporum f.sp.lactucae, although from a low percent of seeds, supports the hypothesis that the rapid spread of Fusarium wilt of lettuce observed recently in Italy is due to the use of infected propagation material. Measures for prevention and control of the disease are discussed. http://www.phytoparasitica.org posting Dec. 16, 2003.     

Rapid detection of Fusarium oxysporum f. sp. lactucae on soil,lettuce seeds and plants using loop‐mediated isothermal amplification

Fusarium oxysporum f. sp. lactucae (FOL) is a soil‐ and seedborne pathogen and the causal agent of fusarium wilt on lettuce. Four races have been identified within FOL, with different worldwide distribution. Several molecular techniques have been used to detect and identify this pathogen; however, not all of them have the optimal characteristics in terms of sensitivity to perform FOL detection in plant and seed material. A loop‐mediated isothermal amplification (LAMP) assay was developed based on the sequence‐characterized amplified region (SCAR) obtained in a previous rapid amplification of polymorphic DNA (RAPD) study. The LAMP assay has been validated according to the EPPO standard PM7/98. The LAMP assay was tested with lettuce seeds, soil and plant material, and can be used successfully to amplify DNA from each of these matrices. In seed lots artificially inoculated with FOL, the detection limit of the LAMP test was 0.004% infected seed.     

Efficacy of biocontrol agents and natural compounds against powdery mildew of zucchini

The activity of different types of natural compounds and of two biofungicides based on Bacillus subtilis and Ampelomyces quisqualis alone and in combination with fungicides was tested against powdery mildew of zucchini. The efficacy was compared to the activity of fungicides used alone in four experimental trials carried out in the open field and under greenhouse conditions. The Podosphaera xanthii population used throughout the work was partially resistant to azoxystrobin, whereas it was susceptible to mychlobutanil. Sulphur plus terpenes and mustard oil consistently controlled powdery mildew, followed by mychlobutanil alone or in combination with A. quisqualis. B. subtilis and A. quisqualis when tested alone were partially effective. The combination of azoxystrobin and B. subtilis only delayed the spread of the pathogen.     

Evaluation of spray programmes for the management of leaf spot incited by Pseudomonas syringae pv. syringae on tomato cv. Cuore di bue

Four experimental trials were carried out in northern Italy under greenhouse conditions against bacterial leaf spot of tomato, incited by Pseudomonas syringae pv. syringae, a disease recently observed in the country. The efficacy of spray programmes, based on the use of several copper-based compounds, acibenzolar-S-methyl, fosetyl Al and two biological control agents, Bacillus subtilis strain QST 713 and Pseudomonas chlororaphis MA 342, was tested. The best results were obtained with the alternation of copper oxychloride, used alone or in mixture with acibenzolar-S-methyl, with acibenzolar-S-methyl, applied for a total of two sprays. Acibenzolar-S-methyl applied alone was also effective. However, due to its possible slight phytotoxic effect, observed in our case in one trial, strategies relying on a limited number of its application are preferred. The efficacy of acibenzolar-S-methyl is higher under lower inoculum conditions. Among the tested copper-based fungicides, copper oxychloride provided the best and most consistent results, with no or limited phytotoxicity. Other copper compounds were much less effective and sometimes caused a reduction in plant height. The disease suppression achieved with B. subtilis strain QST 713 was only partial, while P. chlororaphis was not effective. The advantages of programmes based on rotation of copper compounds and acibenzolar-S-methyl are discussed.