Symptom survey at the leading-edge of Phytophthora xalni expansion in Portugal
The obtained incidence maps will contribute to the design of an appropriate national strategy for affected alder populations in Portugal.
A symptom survey was conducted in four basins from Northern to Southern Portugal (Lima, Mondego, Sado, Mira). In each basin, four to five transects of alder forest were selected, where all alders were registered within 100 m length and 10 m width in each margin. In each transect, the following data were collected:
– transect level data: land use, channel width, substrate…
– tree level data: xy coordinates, geomorphological position, diameter, height, number of trunks, presence of alder decay symptoms (necroses, defoliation, dead branches, decayed branch tips)
Two new experiments were added to this task. The 1st was a germination trial from the higher disease incidence basin (Lima), where 15 symptomatic and 15 asymptomatic mother trees were sampled for cones, extraction and morphological characterization of seeds. Results were presented at a national congress.
The 2nd was a Maternal effects experiment on seedlings originated from the 4 target basins, to study disease effect in the progeny regeneration and stress tolerance. 15 symptomatic and 15 asymptomatic trees from the Lima/Mondego/Sado/Mira basins were sampled for cones. A total of 682 cones and their seeds were morphologically characterized and a germination trial was performed. After 7 months, seedlings were subjected to drought treatments, and assessed by morphological, physiological and biochemical measurements. Biochemical analysis (phenols and sugars) of vegetative and reproductive tissues were done, to evaluate the decline effect on defense compounds.
Results were presented at an international conference, and 2 SCI articles are in preparation. ALNUS team developed a protocol for symptom survey to engage citizen participation, presented at ALNUS Mid Term Meeting.
Figure 1: Map of watersheds in Portugal (left) and the studied transects (black dots). Two examples of transects (right) were all the alders were registered (coloured dots) and sampled for alder decay symptoms.
Variability between populations of alder and its relation to disease tolerance
The obtained data will point to the potential of natural tolerance to the disease.
A screening of A. glutinosa (L.) Gaertn. and A. lusitanica Vít, Douda & Mandák phenotypic, genotypic and cytogenetic variation was performed on 12 alder populations (between 140 and 160 seedlings per population), comprising a large latitudinal gradient with high differences in temperature and precipitation distribution (Fig. 2). Characterization of populations includes:
- Cytogenetic characteristics
- Genome size per population using flow cytometry
- The cytogenetic characterization allowed to distinguish 2 cytotypes: tetraploids (Iberian and Moroccan populations – A. lusitanica) and diploids (north, center and southeast European populations – A. glutinosa). Results were presented in an international congress and published.
- Phenotypic characteristics
- Seed traits and germination
- Morphological parameters, such as height, diameter, total biomass, root-shoot ratio, Specific Leaf Area (SLA) and root length
- Ecophysiological parameters, such as bud break, leaf senescence, photosynthesis, water use efficiency, fluorescence
- Biochemical parameters such as pigments, phenols and sugars
- Genotypic characteristics (ON GOING)
- Genetic diversity within species and populations using microsatellites
The assessment of phenotypic and genotypic variation patterns across Alnus species was presented in international congresses, and an article is under preparation.
Two new studies were added 1) a hydric stress experiment (preceding Task 3) to study the effect of two drought treatments (high and low) on 5 alder populations from Portugal, Spain, Italy, Sweden and Morocco; and 2) comparative study of the morphological and physiological differences between Atlantic and Mediterranean A. lusitanica populations. Results yielded a MSc thesis, presented at an International Summer School and (2) a presentation in an international congress.
Figure 2: Distribution map of Alnus glutinosa from Caudullo et al. (2017) and location of the 12 populations of Alnus sp. sampled for the ALNUS project. Fyris in Sweden (FY), Vltava in Czech Republic (VL), Selune in France (SE), Riederbach in Austria (RI), Arno in Italy (AR), Ibar in Serbia (IB), Furelos in Spain (FU), Bertiandos in Portugal (BE), Jerte in Spain (JT), Torgal in Portugal (TO), Amitis in Greece (AM) and Oued Lekbir in Morocco (OU).
Interaction between performance and disease infection under simulated climatic change scenarios
The results will help to understand the influence of climatic factors to the effect of the pathogen.
A greenhouse experimental trial was established for two-year old seedlings from 11 populations (between 140 and 160 seedlings per population) of A. glutinosa (L.) Gaertn. and A. lusitanica Vít, Douda & Mandák. Seedlings were submitted to a combination of P. xalni inoculation and high temperatures under controlled conditions. Ecophysiological and morphological performances of seedlings were monitored before, during and after the induced stresses. Seedlings responses to pathogen inoculation were evaluated through leaf and stem necrosis throughout the totality of the experiment duration. The interaction of abiotic and biotic stress revealed the most susceptible populations.
Results were presented at 2 international congresses, the Best Practices Manual (BPM) and two SCI articles under preparation.
Figure 3: Distribution map of Alnus glutinosa from Caudullo et al. (2017) and the location of the 11 populations of Alnus sp. used in the greenhouse experiment of task 3. Fyris in Sweden (FY), Vltava in Czech Republic (VL), Selune in France (SE), Riederbach in Austria (RI), Furelos in Spain (FU), Bertiandos in Portugal (BE), Jerte in Spain (JT), Alegrete in Portugal (AL), Torgal in Portugal (TO), Amitis in Greece (AM) and Oued Lekbir in Morocco (OU).
Selection of tolerant plants
Tolerant plants could be used for restoration of affected riparian ecosystems.
All the surviving plants of the heat stress+inoculation trial in task 3 were monitored for decline and mortality. Then, plants that had shown any resistance were selected for a 2nd inoculation, with the same P. xmultiformis isolate. Plants’ decline and mortality were monitored for X days. After the 2nd inoculation, northern European A. glutinosa populations (Sweden and Austria) had the most resistant individuals.
Results will be presented in one SCI article under preparation.
Predictive modelling of alder decline
The results will aid best management practices, by providing a model to predict alder vulnerability across hydrographic networks. (ON GOING)
The Alder Decline Bayesian Network (ADnet) was built throughout the whole project, with an innovative approach integrating diverse sources of information: own empirical data, literature and expert knowledge through participatory methods. The ADnet conceptual model, counts 3 subnets: 1) management factors affecting pathogen introduction; 2) environmental factors affecting pathogen presence and alder infection and 3) ecophysiological factors affecting alder susceptibility to the disease. The conceptual model was discussed with 19 experts from 6 countries during a virtual meeting using focus groups, a participatory elicitation method to incorporate their valuable inputs. A Validation Meeting, and incorporation of the results from Tasks 2 and 3, allowed to define the Conditional Probability Tables. ADnet was completed during 2022 with sensitivity and scenario analysis to evaluate the model performance and to simulate management scenarios.
The methodology development and applications of the ADnet was presented in an international congress. Three SCI papers were published during ADnet development and one with the results is under preparation. ADnet is intended to serve as decision support tool for riparian management and restoration, with a graphical interface for stakeholders and included in the Best Practice Manual.