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ABSTRACT: BACKGROUND: Grapevine downy mildew, caused by Plasmopara viticola, is a very serious disease affectingmainly Vitis vinifera cultivated varieties around the world. Breeding for resistance throughthe crossing with less susceptible species is one of the possible means to reduce the diseaseincidence and the application of fungicides. The hybrid Bianca and some of its siblings areconsidered very promising but their resistance level can vary depending on the pathogenstrain. Moreover, virulent strains characterized by high fitness can represent a potential threatto the hybrid cultivation. RESULTS: The host response and the pathogen virulence were quantitatively assessed by artificiallyinoculating cv Chardonnay, cv Bianca and their siblings with P. viticola isolates derived fromsingle germinating oospores collected in various Italian viticultural areas. The hostphenotypes were classified as susceptible, intermediate and resistant, according to the AreaUnder the Disease Progress Curve caused by the inoculated strain. Host responses in cvBianca and its siblings significantly varied depending on the P. viticola isolates, which in turndiffered in their virulence levels. The fitness of the most virulent strain did not significantlyvary on the different hybrids including Bianca in comparison with the susceptible cvChardonnay, suggesting that no costs are associated with virulence. Among the individualfitness components, only sporangia production was significantly reduced in cv Bianca and insome hybrids. Comparative histological analysis revealed differences between susceptibleand resistant plants in the pathogen diffusion and cytology from 48 h after inoculation onwards. Defence mechanisms included callose depositions in the infected stomata, increasein peroxidase activity, synthesis of phenolic compounds and flavonoids and the necrosis ofstomata and cells immediately surrounding the point of invasion and determined alterations inthe size of the infected areas and in the number of sporangia differentiated. CONCLUSIONS: Some hybrids were able to maintain an intermediate-resistant behaviour even wheninoculated with the most virulent strain. Such hybrids should be considered for further fieldtrials.
BMC Plant Biology 08/2012; 12(1):124. · 3.45 Impact Factor
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ABSTRACT: QoI resistance in P. viticola was first detected in France and Italy in 1999. Molecular and biological assays have been carried out since 2000 in order
to provide reliable methods of detecting and quantifying resistance. Oospores were collected in vineyards located in northern
and southern Italy. QoI resistance was evaluated by the germination rate of oospores on azoxystrobin amended medium and the
frequency of mutant alleles in the DNA extracted from oospores. Both methods correlated to each other and were used side by
side to test QoI resistance. Due to the spontaneous occurrence of the G143A mutation in wild type populations and the immigration
from surrounding vineyards, resistance frequencies up to 10% were found in samples collected from vineyards never treated
with QoIs. Particularly high values, about 90%, were associated with the application of five to six QoI treatments within
the same season, while lower percentages, about 30%, were detected in vineyards treated with QoI used in mixture with fungicides
belonging to a different resistance group. A progressive decrease of resistance frequency was observed when QoI applications
were reduced in number or completely suspended for at least one season. Therefore, a full recovery of sensitivity may be achieved
even in vineyards characterized by high levels of resistance, if particular care is taken during disease control by using
QoIs only in mixtures and reducing the number of QoI treatments.
KeywordsDowny mildew–Fungicide resistance–Grapevine–Resistance management–Sensitivity assay
European Journal of Plant Pathology 04/2012; 129(2):331-338. · 1.41 Impact Factor
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ABSTRACT: Oospores, the only overwintering structures of Plasmopara viticola, the causal agent of grapevine downy mildew, are the unique source of inoculum for primary infections in vineyards. We show
that their germination dynamics depend on both climatic and endogenous factors. In particular, overwintering in controlled
conditions suggests that low temperatures prolong the oospore germinability, while constant or gradually alternating water
availability increases germination rates. However, wide fluctuations in germination percentage, observed both in naturally
overwintered oospores, and under controlled conditions, indicate an important role for endogenous factors in the germination
frequency. Ad hoc experimental assays and microscopic observations highlight an important role for calcium in the germination process. However,
for a profound understanding of the biological mechanisms underlying oospore germination, mathematical models of the germination
dynamics are needed. But, classical differential models of germination dynamics are, with current knowledge, prohibitive due
both to the complexity of the underlying processes and knowledge incompleteness. Then, we propose a hybrid method derived
from the integration of qualitative differential models and fuzzy systems.
KeywordsDowny mildew-Calcium signalling-Grapevine-Mathematical modelling-System identification
European Journal of Plant Pathology 04/2012; 128(1):113-126. · 1.41 Impact Factor
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ABSTRACT: Fusarium verticillioides, the most common causal organism of Fusarium stalk and ear rot of maize in Northern Italy, produces important mycotoxins such as fumonisins. Reproductive biology of F. verticillioides has been widely studied in numerous maize growing areas, but up to now no information is available on the mating behavior and genetic structure of this plant pathogen in Italy. Mating type and female fertility distribution and effective population number, N ( e ), were assessed for a population of 181 F. verticillioides strains isolated from three fields located in Lombardia region (Northern Italy) during 2007-2008 maize growing season. The ratio of MAT-1:MAT-2 was significantly different from the theoretical 1:1 ratio expected in an idealized population in which individuals mate at random. The frequency of hermaphroditic strains was 20 % of the total population. N ( e ) for mating type was 89 % of the count (total population) and the N ( e ) for male or hermaphrodite status was 55 %. The number of isolates that can function as the female parent limited N ( e ) in the examined population. Under equilibrium cycle, assuming that female fertility has been lost due to selection and mutation rate during asexual reproduction, sexual reproduction needed to occur only once per 40 to 118 asexual generations to maintain this level of sexual fertility.
Journal of applied genetics 04/2011; 52(3):367-70. · 1.66 Impact Factor
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ABSTRACT: The mandelic acid amide, mandipropamid, which belongs to the carboxylic acid amide (CAA) fungicides, is active against Plasmopara viticola, the causal agent of grapevine downy mildew. The fungicide primarily inhibits the germination of encysted zoospores, thus preventing the pathogen’s penetration into the host tissues, but it also shows curative effects. In this study, the infection structures of P. viticola in both leaves and berries were investigated to detect the histological and ultrastructural alterations induced by mandipropamid when applied after inoculation. Compared to the untreated samples characterized by a diffuse colonization of the tissues and by a normal ultrastructure of the pathogen, the application of mandipropamid 24 h after inoculation with P. viticola reduced pathogen colonization in leaves and berries. In addition, detachment of the plasmalemma from the hyphal and haustorial walls was observed 72 h after inoculation. In the berries, an abnormal proliferation of the pathogen plasma membrane was observed. Collapsed hyphae and haustoria in treated leaves were surrounded by callose or encapsulated in an amorphous material inside the host cell 72 h after inoculation, while a similar effect was observed in later stages (7 days) in berries. The results confirm that mandipropamid, which acts at the interface between the pathogen plasmalemma and cell wall, has curative activity against P. viticola, appearing more rapidly in leaves than in berries.
Journal of Phytopathology 09/2010; 159(4):201 - 207. · 0.79 Impact Factor
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ABSTRACT: QoI fungicides, inhibitors of mitochondrial respiration at the Qo site of cytochrome b in the mitochondrial bc(1) enzyme complex, are commonly applied in vineyards against Plasmopara viticola (Berk. & MA Curtis) Berl. & De Toni. Numerous treatments per year with QoI fungicides can lead to the selection of resistant strains in the pathogen population owing to the very specific and efficient mode of action. In order to evaluate the resistance risk and its development, two different methods, biological and molecular, were applied to measure the sensitivity of oospores differentiated in vineyards, both treated and untreated with azoxystrobin, from 2000 to 2004. Assays using oospores have the advantage of analysing the sensitivity of bulked samples randomly collected in vineyards, describing accurately the status of resistance at the end of the grapevine growing season. Both methods correlated well in describing the resistance situation in vineyards. QoI resistance was not observed in one vineyard never treated with QoI fungicides. In the vineyard where azoxystrobin had been used in mixture with folpet, the selection of QoI-resistant strains was lower, compared with using solely QoI. In vineyards where QoI treatments have been stopped, a decrease in resistance was generally observed.
Pest Management Science 03/2007; 63(2):194-201. · 2.25 Impact Factor
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ABSTRACT: Investigations carried out on secondary metabolites produced in culture by a hypovirulent strain of Cryphonectria parasitica allowed the isolation of several compounds which were characterized by NMR analysis and derivatization reactions. The most abundant metabolite was a new compound, called cryphonectric acid (1). Other metabolites were diaporthin, the only known phytotoxic compound isolated from both virulent and hypovirulent strains of C. parasitica, (+)-orthosporin, and L-p-hydroxyphenyllactic acid (HOPLA). Root growth activity of the purified compounds was evaluated both on tomato seedlings and maize subapical segments.
Journal of Natural Products 02/2002; 65(1):48-50. · 3.13 Impact Factor
