Michele Scotton

Distinct colonization patterns and cDNA-AFLP transcriptome profiles in compatible and incompatible interactions between melon and different races of Fusarium oxysporum f. sp. melonis

BackgroundFusarium oxysporum f. sp. melonis Snyd. & Hans. (FOM) causes Fusarium wilt, the most important infectious disease of melon (Cucumis melo L.). The four known races of this pathogen can be distinguished only by infection on appropriate cultivars. No molecular tools are available that can discriminate among the races, and the molecular basis of compatibility and disease progression are poorly understood. Resistance to races 1 and 2 is controlled by a single dominant gene, whereas only partial polygenic resistance to race 1,2 has been described. We carried out a large-scale cDNA-AFLP analysis to identify host genes potentially related to resistance and susceptibility as well as fungal genes associated with the infection process. At the same time, a systematic reisolation procedure on infected stems allowed us to monitor fungal colonization in compatible and incompatible host-pathogen combinations.ResultsMelon plants (cv. Charentais Fom-2), which are susceptible to race 1,2 and resistant to race 1, were artificially infected with a race 1 strain of FOM or one of two race 1,2 w strains. Host colonization of stems was assessed at 1, 2, 4, 8, 14, 16, 18 and 21 days post inoculation (dpi), and the fungus was reisolated from infected plants. Markedly different colonization patterns were observed in compatible and incompatible host-pathogen combinations. Five time points from the symptomless early stage (2 dpi) to obvious wilting symptoms (21 dpi) were considered for cDNA-AFLP analysis. After successful sequencing of 627 transcript-derived fragments (TDFs) differentially expressed in infected plants, homology searching retrieved 305 melon transcripts, 195 FOM transcripts expressed in planta and 127 orphan TDFs. RNA samples from FOM colonies of the three strains grown in vitro were also included in the analysis to facilitate the detection of in planta-specific transcripts and to identify TDFs differentially expressed among races/strains.ConclusionOur data suggest that resistance against FOM in melon involves only limited transcriptional changes, and that wilting symptoms could derive, at least partially, from an active plant response.We discuss the pathogen-derived transcripts expressed in planta during the infection process and potentially related to virulence functions, as well as transcripts that are differentially expressed between the two FOM races grown in vitro. These transcripts provide candidate sequences that can be further tested for their ability to distinguish between races.Sequence data from this article have been deposited in GenBank, Accession Numbers: HO867279-HO867981.

Seed Harvesting for Ecological Restoration: Efficiency of Haymaking and Seed-Stripping on Different Grassland Types in the Eastern Italian Alps

Haymaking and seed-stripping are frequently utilized methods of obtaining seeds for use in ecological restoration. We sought to measure the efficiency of these two techniques in different grassland types in terms of the seed mix obtained compared to the seed present in the vegetation. Haymaking and harvesting with a pull-type seed stripper were compared in two different types of eastern Italian Alp meadows: a tall oats (Arrhenatherum elatius) meadow (grass height 70–100 cm) and a low fescue-bentgrass (Festuca nigrescens—Agrostis capillaris) meadow (grass height 35–65 cm). The percentage of seed obtained from haymaking was similar to that obtained from seed-stripping (about 50% of the seed in the standing vegetation). Nevertheless, haymaking efficiency differed less among the two grassland types (with reference to the harvested seeds number per fertile stem, 39% in the tallgrass and 60% in the shortgrass vegetation) compared to the efficiency of seed-stripping (20% and 73%, respectively). With haymaking, the seed mix obtained in both meadows was similar to that present in the standing vegetation before harvesting. With seed-stripping, the similarity was high only in the shortgrass meadow, where the stripping action of the brush affected the whole herbaceous layer, and the downward motion of the brush allowed for effective harvesting. Both techniques were more efficient in the shortgrass meadow than in the tallgrass vegetation.

Hydrochemistry, water table depth and related distribution patterns of vascular plants in a mixed mire

Abstract The hydrological and floristic variation within a mire vegetation is mostly controlled by three ecological gradients: nutrient availability, acidity – alkalinity, and water table depth. The objectives of this study were: (a) to analyse the hydrochemistry of a mixed mire in relation to different habitat conditions; (b) to evaluate the patterns of vascular plant composition in relation to nutrient availability, acidity – alkainity, and water table depth, and to partition the pure effects of these gradients. Within a mixed mire, we sampled 36 smalling a growing season. Water chemistry proved to be significantly different between the various vegetation types. Two biological systems could be identified according to hydrochemistry and vascular plant composition: (1) several fen vegetation types lacking raised Sphagnum structures where the water chemistry reflected groundwater properties; (2) bog Sphagnum-dominated vegetation, where the convex shape of the mire surface prevented mixing with the groundwater. The results of the partitioning indicated that the acidity – alkalinity gradient was more important in controlling the patterns of plant distribution than water table depth.

Environmental and Pathogenic Factors Inducing Brown Apical Necrosis on Fruit of English (Persian) Walnut

Brown apical necrosis (BAN) is a most recently described disease affecting English (Persian) walnut fruit. BAN was only recorded in intensively managed walnut orchards and was found to be a disease complex mainly caused by Fusarium species. All fungi associated with this disease are polyphagous and ubiquitous, not specific to walnut. Consequently, BAN occurrence is more strictly dependent, than generally, on the interaction between pathological features and environmental conditions. Environmental variables identified with regression analysis showed that maximum temperature, angle of main wind direction versus tree row orientation, and orchard distance to the closest river/canal, all representative of climatic conditions occurring in the orchard, were related to fruit drop. The factor displaying the highest influence on severity of BAN fruit drop was maximum temperature and only subordinately factors are associated with relative humidity. BAN symptoms were reproduced with in planta artificial inoculation, and fruit drop of symptomatic fruit was significantly higher than that of the noninoculated trees for each type of inoculum (Fusarium semitectum, F. graminearum, and Alternaria spp.). F. semitectum and F. graminearum were more aggressive than Alternaria species, and the earliest artificial inoculations in mid-May resulted in the highest fruit drop. The extension of walnut fruit susceptibility and the conducive environmental factors to BAN are discussed.

Wild Seed Harvesting at Mountainous Species-Rich Grassland in Calcareous Italian Alps

ABSTRACT Wild harvesting is an efficient option for supplying seed to be used for restoring seminatural grasslands. Several methods are currently used to implement wild harvesting, but few controlled experiments have investigated its efficiency regarding seed amount and number of species collected. A harvesting trial was conducted in a species-rich, low-productivity grassland of the calcareous Italian Alps (1 030 m above sea level [a.s.l.). Three mechanical methods were tested in three replications using a completely randomized block design: green hay (GH), dry hay (DH), and seed stripping (SS) harvesting. The number of fertile shoots, mature seeds, and species collected was recorded and compared with the standing seed yield (SSY). GH, DH, and SS harvested approximately 84%, 70%, and 29% of SSY, respectively. Forbs were harvested more efficiently than grasses in all methods but in most cases at very low seed amounts per m2 due to their low seed density for SSY. No significant difference among methods was found for the number of species collected as mature seeds, but SS, implemented on larger plots, tended to collect more forb species. Comparing the results with those of other experiments demonstrated that the relatively cool temperature of the seed maturation period at the mountain site favored stronger seed retention and therefore increased the GH and DH efficiency but decreased the SS efficiency. In cool mountain areas, wild harvesting from forb-rich grasslands should bemore successful by SS implemented on wide areas and several times over the vegetative season. In less species-rich grassland, GH and DH can efficiently collect high seed amounts of the fewer species present, even if implemented over smaller areas.

Efficiency and allometry of seed production in grassland forbs: site and year comparative study in the Italian Eastern Pre-Alps

Abstract Forbs are important biodiversity components of grasslands and are often threatened by management intensification. As most forbs propagate predominantly by seed, knowledge of their seed regenerative traits would improve the conservation and restoration of forb-rich ecosystems. The main seed production traits of six forbs that are common in European species-rich grasslands were studied by collecting fertile shoots from different sites and over several years. Among sites and years, variability was high, particularly in the number of inflorescences per shoot, which affected ovule production more than any other trait. Relationships between inflorescence size and the number of ovules were mainly negatively allometric or almost so, with lower flower densities in larger inflorescences. The average ovule-to-seed transformation efficiency was 58%. There was significant variation among collections of the same species, and even more between species. Species with a low ovule-to-seed transformation efficiency generally exhibited compensatory, high seed viability. Large inflorescences had high ovule to seed utilization values, probably because of better nutrient conditions. Seed germinability (average, 30%) was much lower than seed viability (average, 54%); therefore, seed dormancy was an important feature of the species studied.

Fusarium oxysporum f. Sp. melonis-melon interaction: Effect of grafting combination on pathogen gene expression

This work is part of a comprehensive study addressed to gain new insights into Fusarium oxysporum f. sp. melonis (FOM)-melon interaction and understand molecular mechanisms of disease control by grafting. Grafting vegetable is primarily used to provide resistance to soilborne diseases. In this study, the effect on FOM race 1 and race 1,2 gene expression was investigated by quantitative PCR (qPCR), during infection of both resistant and susceptible grafted melon scion-rootstock combinations. Eleven fungal genes related to pathogenicity were considered. The expression of the selected genes varied according to race, susceptible or resistant interaction, and time clustering into six profiles. Classical infection related genes, including Zn-Cys transcription factor FOW2, xylanase, and its relative transcriptional activator were highly induced particularly in the resistant combination when infected by race 1,2 at any time point. In turn, ROS degrading catalase/peroxidase enzyme and actin binding protein were upregulated only at the early stage of infection, in both resistant and susceptible combinations. Genes such as E3 ubiquitin-protein ligase and UTP-glucose-1-phosphate uridylyl transferase showed significant differences between both FOM races in both grafting combinations. Whereas MADS-box transcription factor and acyl-CoA synthetase were essentially unmodulated in race 1, but induced in race 1,2. The only gene significantly dependent on fungal race, resistant/susceptible interaction, and time, was a histidine kinase. Temporal transcription profiles were consistent with the capacity of race 1,2 to grow in the resistant host without inducing wilting symptoms being race 1,2 host colonization independent from virulence. In general, single FOM gene transcription profiles showed no evident differences between rootstock and scion confirming at a molecular level that a melon grafted plant reacts to the pathogen as a single genotype ruled by the rootstock.