Differences in the efficacy of carboxylic acid amide fungicides against less sensitive strains of Plasmopara viticola.

BACKGROUND: Plasmopara viticola is controlled by fungicides with different modes of action, including carboxylic acid amides (CAAs). The aim of this study was to evaluate differences in the response of CAA-resistant P. viticola strains towards CAAs. RESULTS: The G1105S mutation affects all four CAAs, but with different impacts. While this confirms that they have the same mode of action, it shows that differences between CAAs can occur. CONCLUSION: Further molecular modelling and docking studies are needed to gain a better understanding of the different behaviours reported here. © 2015 Society of Chemical Industry.

Genetic diversity analysis of the cucurbit powdery mildew fungus Podosphaera xanthii suggests a clonal population structure.

The sexual stage of Podosphaera xanthii is rarely found worldwide. However, chasmothecia are frequently recorded in northern Italy, suggesting the presence of an actively mating population. With the aim of investigating the genetic structure of the Italian population with respect to populations from other countries, genetic diversity analysis was performed both on 92 isolates from European and American countries by multilocus sequence typing (MLST) and on 59 isolates by amplified fragment length polymorphism (AFLP) methods. Mating type frequencies were tested for random mating and two-locus linkage disequilibrium (LD) analysis was performed. Results showed very low levels of genetic diversity: MLST showed no variations in eight housekeeping gene fragments and, accordingly, UPGMA dendrogram from AFLP data showed a high similarity (0.91-1.00 simple matching similarity coefficient) between isolates. Moreover, the random mating test showed no deviations from mating-type 1:1 ratio in the Italian population but deviations were observed in populations from Europe and American countries while two-locus LD analysis showed the presence of significant LD. The results suggest that the populations of P. xanthii are likely to be predominantly clonal, and asexual reproduction, producing a huge amount of conidia, appears to be the predominant type of reproduction of the species.

New rapid DNA extraction method with Chelex from Venturia inaequalis spores.

The objective of this study was to develop a rapid method to isolate DNA from Venturia inaequalis spores for use in diagnostic DNA mutation analysis. Chelex-100 resin was evaluated and compared with a well established DNA exctraction method, utilizing CTAB in order to have a robust comparison. In this research we demonstrated that Chelex-100 efficiently makes extraction of the DNA from V. inaequalis spores available for direct use in molecular analyses. Also, the quantity and quality of extracted DNA were shown to be adequate for PCR analysis. Comparatively, the quality of DNA samples isolated using Chelex method was better than those extracted using CTAB. In conclusion, the Chelex method is recommended for PCR experiments considering its simplicity and cost-effectiveness.

Sensitivity to strobilurin fungicides of Italian Venturia inaequalis populations with different origin and scab control.

BACKGROUND: Venturia inaequalis (Cooke) Winter with reduced sensitivity to strobilurins has been reported in several countries, including Italy. This study aimed to characterise the sensitivity to strobilurins of three different types of V. inaequalis population: (a) wild types; (b) from commercial orchards satisfactorily managed with strobilurins; (c) from an experimental orchard with control failures by trifloxystrobin and kresoxim-methyl. In vitro sensitivity tests included antigerminative activity on population conidia and mycelial growth inhibition on monoconidial isolates. Cleaved amplified polymorphic sequence (CAPS) analysis was used for the detection of G143A substitution. RESULTS: Wild-type populations showed EC(50) values lower than 0.031 mg L(-1), while those of orchards with good performance by strobilurins presented EC(50) values never higher than 0.063 mg L(-1). Samples with scab control failures showed a strongly reduced population sensitivity. Similar differences were confirmed in monoconidial isolates. The G143A substitution was always detected in low-sensitivity populations, only sometimes in well-controlled populations and generally not in wild types. CONCLUSIONS: In vitro sensitivity assays were able to discriminate the three population types with different scab management, while the qualitative PCR analysis (CAPS) was only partially reliable. High sensitivity differences among V. inaequalis populations with good and poor field control by strobilurins were observed.