Biomass production, foliar and root characteristics and nutrient accumulation in young silver birch (Betula pendula Roth.) stand growing on abandoned agricultural land

The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics of a 8-year-old silver birch (Betula pendula) natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current annual production after eight growing seasons was 31.2 and 11.9 t DM ha⁻¹, respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass of the stand. Carbon sequestration in tree biomass reaches roughly 17.5 t C ha⁻¹ during the first 8 years. The biomass of the fine roots (d < 2 mm) was 1.7 ± 0.2 t DM ha⁻¹ and 76.2% of it was located in the 20 cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7 m² m⁻² and specific leaf area (SLA) 15.0 ± 0.1 m² kg⁻¹. The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared with the lower part. The short-root specific area (SRA) in the 30 cm topsoil was 182.9 ± 9.5 m² kg⁻¹, specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry mass unit of short roots were 145.3 ± 8.6 m g⁻¹, 58.6 ± 3.0 kg m⁻³ and 103.7 ± 5.5 tips mg⁻¹, respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6, 25.0 and 56.6 kg ha⁻¹, respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7 kg ha⁻¹ yr⁻¹ (55 and 27%), respectively, of which 29.1 kg ha⁻¹ N and 2.8 kg ha⁻¹ P were accumulated in the above-ground part of the stand.     

A regret function for agricultural production systems

Decision-making under uncertainty is a difficult task, involving risks. Since losses are to be expected although not necessarily through the decision-maker's fault, a regret concept is adopted. A regret concept and a regret function, based on a linear programming model, are suggested, using analysis of the sensitivity of the optimal plan to changes in random prices and in the amounts of available resources and estimates of the probabilities that each of the random variables will drop below a critical value. The use of this regret function, as an aid in decision-making, to evaluate the plan at the planning stage is explained and clarified by examples and a case study.     

Analysis and assessment of precipitation chemistry at Caribou,Maine

Over the last 30 yr, Caribou, Maine has been the only U.S. collection site which has been a part of all four national precipitation chemistry networks. Due to its remote but strategically important location, the data from this site are very useful in evaluating transboundary transport of the major ions present in precipitation. This paper assesses the reliability of the Caribou data base and looks at the more recent data with the aid of the GAMBIT (Gridded Atmospheric Multilevel Backward Isobaric Trajectory) model. An examination of the historical data base indicates serious contamination problems in pre-1980 samples, particularly with S0₄ measurements. The trajectory climatology shows that the largest number of precipitation events track along the U.S. coast. Preliminary chemistry measurements indicate highest concentrations of H+ and S0₄ occur from events associated with trajectories passing through southern Canada.     

Inter-laboratory evaluation of a duplex RT-PCR method using crude extracts for the simultaneous detection of Prune dwarf virus and Prunus necrotic ringspot virus

The operational capacity of a duplex RT-PCR method for simultaneous detection of Prune dwarf virus (PDV) and Prunus necrotic ringspot virus (PNRSV) has been established by nine European laboratories. A total of 576 samples from Prunus trees with known sanitary status, corresponding to 32 samples in two repetitions for each laboratory, were analysed. The level of sensitivity achieved by the method was 98.3% for PDV and 90.4% for PNRSV. The specificity was 87.4% for PDV and 94.3% for PNRSV. The unilateral 95% confidence intervals were calculated for all these values. Cohen’s Kappa coefficient of repeatability and reproducibility of the technique indicated a strong agreement between data. Likelihood ratios were 7.50 (positive) and 0.02 (negative) for PDV. For PNRSV, the positive likelihood ratio was 15.00 while the negative likelihood ratio was 0.11. In addition, post-test probabilities of infection were calculated to manage the risk associated with the routine use of this method. This allows an accurate test result interpretation to facilitate the integration of this new technique into a certification scheme.     

Incidence and distribution of ‘Candidatus Phytoplasma prunorum’ and its vector Cacopsylla pruni in Spain: an approach to the epidemiology of the disease and the role of wild Prunus

‘Candidatus Phytoplasma prunorum’ is the causal agent of the European stone fruit yellows (ESFY) disease. This phytoplasma affects wild and cultivated species of Prunus to different degrees, depending on their susceptibility. ‘Candidatus Phytoplasma prunorum’ is present in the four regions of Spain surveyed in this study (Aragon, Catalonia, Extremadura and Valencia) with a variable incidence. Results showed that ‘Ca. Phytoplasma prunorum’ was detected in all of the cultivated Prunus species studied, except P. avium and P. dulcis, and was widespread in Spain. The most affected species was P. salicina, with symptoms including early bud break and blooming, leaf curling and yellowing, collapse, and a major decrease in production. In some plots in the Baix Llobregat area of Barcelona province (Catalonia), the incidence of ESFY on P. salicina was as high as 80%. The insect vector, Cacopsylla pruni, was present in all four of the regions studied, with the highest captures in yellow sticky traps in Catalonia on P. mahaleb and in Extremadura in peach orchards. In Baix Llobregat, large populations of C. pruni were present on infected P. mahaleb bushes, and with high infection rates. This was a key factor in the local pathogenic cycle that caused a major ESFY outbreak in the nearby P. salicina orchards. In the Ebro valley (Lleida and Aragon) and Valencia, the surveys showed very low incidences of the disease and low C. pruni populations.     

Role of <Emphasis Type="Italic">Cacopsylla pyri</Emphasis> in the epidemiology of pear decline in Spain

The frequency of pear decline-positive insects and transmission of pear decline (PD) phytoplasma by Cacopsylla pyri in Spain has been studied. Psyllids were used for experiments on phytoplasma transmission both to healthy Pyrus communis trees and to an artificial feeding medium. Over a period of 1 year, about 100 psyllids were collected monthly from pear trees, cv. Williams, using the beating tray method, and tested for the presence of PD phytoplasma. Results indicate that the frequency of PD positive psyllids changes through the year and that C. pyri transmits the pear decline associated disease agent. Phytoplasma transmission was also effective under laboratory conditions using a feeding medium. The relationship between PD positive Cacopsylla pyri, Pear decline phytoplasma transmission and the sex of the vector was also evaluated. Although the percentage of PD positive psyllids was similar in both genders, PD phytoplasma transmission by females was significantly higher than by males. Since the sex ratio (male/female) was less than 1:1 for most of the year, these results should be taken into consideration for controlling Pear decline in Mediterranean climates.     

Transmission of ‘Candidatus Phytoplasma pyri’ by naturally infected Cacopsylla pyri to peach,an approach to the epidemiology of peach yellow leaf roll (PYLR) in Spain

Peach orchards in the northeast of Spain were severely affected in 2012 by a previously unreported disease in this area. The symptoms included early reddening, leaf curling, decline, abnormal fruits, and in some cases death of the peach trees. All the infected peach samples were positive for ‘Candidatus Phytoplasma pyri’, but none were infected by the ‘Ca. Phytoplasma prunorum’. In this work, potential vectors able to transmit ‘Ca. Phytoplasma pyri’ from pear to peach and between peach trees were studied and their infective potential was analysed at different times of the year. Transmission trials of the phytoplasma with potential vectors to an artificial feeding medium for insects and to healthy peach trees were conducted. Additionally, isolated phytoplasmas were genetically characterized to determine which isolates were able to infect peach trees. Results showed that the only insect species captured inside peach plots that was a carrier of the ‘Ca. Phytoplasma pyri’ phytoplasma was Cacopsylla pyri. Other insect species captured and known to be phytoplasma transmitters were present in very low numbers, and were not infected with ‘Ca. Phytoplasma pyri’ phytoplasma. A total of 1928 individuals of C. pyri were captured in the peach orchards, of which around 49% were phytoplasma carriers. All the peach trees exposed to C. pyri in 2014, and 65% in 2015, were infected by ‘Ca. Phytoplasma pyri’ 1 year after exposure, showing that this species is able to transmit the phytoplasma to peach. Molecular characterization showed that some genotypes are preferentially determined in peach.     

Spatial distribution of water status in irrigated olive orchards by thermal imaging

Information regarding tree water status in irrigated olive orchards is essential for managing growth to optimize yields and olive oil quality. One management practice option is to monitor or sample individual trees and use this information for orchard-scale management. This study assessed the ability of thermal imaging to provide the spatial distribution and variability of tree water status in a commercial irrigated olive orchard, and described strategies and a procedure for choosing which individual trees best represent the orchard. The study employed gradual upscaling from individual trees grown in lysimeters, through a controlled experimental field plot, to a commercial orchard. Thermal imaging of olive trees grown in lysimeters attested the sensitivity of the technique to identify mild-level water stress by correlating crown temperatures to stem water potential. Knowledgeable choice of five or ten representative trees in the experimental plot, based on the histogram distribution obtained for the entire experimental orchard, lead to successful reconstruction of the spatial distribution of canopy temperature, and thus of water status. Positively skewed distributions of crown temperatures found in both the field plot and commercial orchard suggested distinct patterns, where the canopy temperature of the majority of the trees was lower than the average, and a relatively small number of trees had significantly higher temperatures and suggest commercial practicality of the proposed methodology. Thermal imaging can therefore serve as a useful tool for determining representative trees that, if frequently monitored, or instrumented with continuous water status sensors, can provide important information for orchard water management.     

Assessment of genetic relatedness in carnation by DNA fingerprint analysis

Summary DNA fingerprinting analysis of genetic relatedness between carnation genotypes using human derived minisatellite probes, correctly reflected relationships within and between categories of carnation plants with inferred relatedness. Similar DNA fingerprint patterns were observed between genotypes within either standard or spray categories. A high level of similarity was also detected between those categories. Moderate similarities were found within the dwarf category, and between dwarf and either standard or spray categories. Large differences were observed between a wild species and cultivated categories. Abbreviations: b.1.-breeding line, BS-band-sharing