Genetic diversity of the myrtle rust pathogen (Austropuccinia psidii) in the Americas and Hawaii: Global implications for invasive threat assessments

Since the myrtle rust pathogen (Austropuccinia psidii) was first reported (as Puccinia psidii) in Brazil on guava (Psidium guajava) in 1884, it has been found infecting diverse myrtaceous species. Because A. psidii has recently spread rapidly worldwide with an extensive host range, genetic and genotypic diversities were evaluated within and among A. psidii populations in its putative native range and other areas of myrtle rust emergence in the Americas and Hawaii. Microsatellite markers revealed several unique multilocus genotypes (MLGs), which grouped isolates into nine distinct genetic clusters [C1–C9 comprising C1: from diverse hosts from Costa Rica, Jamaica, Mexico, Puerto Rico, and USA‐Hawaii, and USA‐California; C2: from eucalypts (Eucalyptus spp.) in Brazil/Uruguay and rose apple (Syzygium jambos) in Brazil; C3: from eucalypts in Brazil; C4: from diverse hosts in USA‐Florida; C5: from Java plum (Syzygium cumini) in Brazil; C6: from guava and Brazilian guava (Psidium guineense) in Brazil; C7: from pitanga (Eugenia uniflora) in Brazil; C8: from allspice (Pimenta dioica) in Jamaica and sweet flower (Myrrhinium atropurpureum) in Uruguay; C9: from jabuticaba (Myrciaria cauliflora) in Brazil]. The C1 cluster, which included a single MLG infecting diverse host in many geographic regions, and the closely related C4 cluster are considered as a “Pandemic biotype,” associated with myrtle rust emergence in Central America, the Caribbean, USA‐Florida, USA‐Hawaii, Australia, China‐Hainan, New Caledonia, Indonesia and Colombia. Based on 19 bioclimatic variables and documented occurrences of A. psidii contrasted with reduced sets of specific genetic clusters (subnetworks, considered as biotypes), maximum entropy bioclimatic modelling was used to predict geographic locations with suitable climate for A. psidii which are at risk from invasion. The genetic diversity of A. psidii throughout the Americas and Hawaii demonstrates the importance of recognizing biotypes when assessing the invasive threats posed by A. psidii around the globe.     

Considering neighborhood effects improves individual dbh growth models for natural mixed-species forests in Mexico

Key message

More accurate diameter at breast height (dbh)-growth models are needed for developing management tools for mixed-species forests in Mexico. Individual distance-dependent dbh growth models that quantify local neighborhood effects have been developed for four species groups in such forests. The performance of the models is improved by distinguishing between inter- and intraspecific group competitions.

Context

The management of mixed-species forests in the northwest of Durango, Mexico, is mainly based on the selection method. Understanding the interspecific and intraspecific competition is critical to developing management tools for such mixed-species forests.

Aims

An individual-based distance-dependent modeling approach was used to model the growth of dbh and to evaluate neighborhood effects for four species groups in Mexican mixed-species stands.

Methods

Twenty-two species were classified into four groups: Pinus (seven species), other conifers (three species), other broadleaves (four species), and Quercus (eight species). Four methods were used to select neighboring trees and 12 competition indices (CIs) were calculated. Comparisons of the neighboring trees selection methods and CIs and tests of assumptions about neighborhood effects were conducted.

Results

Intra-species-group competition significantly reduced diameter growth for all species groups, except for the Quercus group. The Pinus, other conifers, and Quercus groups had significant and negative neighborhood effects on the other broadleaves species group, and not vice versa. The Quercus group also had negative neighborhood effect on the Pinus and other conifers species groups, and not vice versa. The Pinus and other conifers species groups had negative neighborhood effects on each other. All fitted age-independent dbh growth models showed a good of fit to the data (adjusted coefficient of determination larger than 0.977).

Conclusion

The growth models can be used to predict dbh growth for species groups and competition in mixed-species stand from Durango, Mexico.

     

When the ground cover brings guests: is <Emphasis Type="Italic">Anaphothrips obscurus</Emphasis> a friend or a foe for the biological control of <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in clementines?

Biological control of Tetranychus urticae Koch (Acari: Tetranychidae), a key pest of clementines, can be improved in this crop with the establishment of a ground cover of Festuca arundinacea Schreber (Poaceae). This cover houses an abundant and diverse community of predatory Phytoseiidae mites including Euseius stipulatus (Athias-Henriot), Neoseiulus barkeri Hughes, Neoseiulus californicus (McGregor) and Phytoseiulus persimilis Athias-Henriot and a dense population of the grass thrips Anaphothrips obscurus Müller (Thysanoptera: Thripidae) throughout the year. The aim of this study was to determine whether the presence of this thrips species could be related to the improvement in the biological control of T. urticae. Therefore, the capacity of the abovementioned phytoseiids to feed and reproduce on A. obscurus and their feeding preferences when T. urticae and A. obscurus were simultaneously offered, were analyzed. The results show that E. stipulatus, N. barkeri and N. californicus have a type II functional response when offered A. obscurus nymphs, whereas P. persimilis barely feeds on this thrips species. Furthermore, N. barkeri and N. californicus can reproduce feeding only on thrips. Regarding prey preference, the Tetranychus spp.-specialist P. persimilis preferably preyed on T. urticae, the generalists N. barkeri and E. stipulatus preferred A. obscurus, and the selective predator of tetranychid mites N. californicus showed no preference. Therefore, we hypothesize that the enhanced biological control of T. urticae observed could be related to A. obscurus becoming an alternative prey for non-specialist phytoseiids, without altering the control exerted by the T. urticae-specialist P. persimilis and likely reducing intraguild predation.     

Geographic variation in pheromone component ratio and antennal responses,but not in attraction,to sex pheromones among fall armyworm populations infesting corn in Mexico

The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is one of the most important pests of corn in Latin America. This insect presents two strains with behavioural and genetic differences. In Mexico, both strains are present, and at least two different FAW populations have been reported within the corn-strain. The objective of this study was to gather evidence of whether pheromonal communication varies among different S. frugiperda populations infesting corn in Mexico. First, we investigated any qualitative or quantitative difference in the composition of sex pheromones among populations; second, we studied whether male antennal responses to pheromone components vary among populations; and, finally, we investigated whether males from a region can discriminate between a synthetic pheromone blend characteristic of their region and blends formulated with the ratio of pheromone compounds emitted by females from other populations. Sex pheromone components were sampled by solid-phase microextraction and identified by gas chromatography coupled to mass spectrometry. Females from all populations consistently released three compounds: (Z)-9-tetradecenyl acetate (Z9-14:OAc), (Z)-11-hexadecenyl acetate (Z11-16:OAc) and (Z)-7-dodecenyl acetate (Z7-12:OAc). Our results showed that Z9-14:OAc and Z7-12:OAc evoked the highest and most variable antennal responses among the populations studied compared to Z11-16:OAc. However, males did not discriminate between local pheromone blends and those formulated from other populations in a field test. These results show that although there is geographic variation in the ratio of pheromone components and in the peripheral reception of them, males were not differentially attracted to different pheromone blends in the field.     

Implementation of a low-cost crop detection prototype for selective spraying in greenhouses

During phytosanitary treatments aimed at minimizing product losses, selective spraying systems can be employed. These systems consist of a group of detection–action devices which manage the spraying. In this work, the technical feasibility of a low-cost ultrasound detection system prototype has been assessed for pesticide spray application on greenhouse crops. The prototype is based on a commercially-available car parking assistance system, which has been modified to amplify the signal and activate an electro-valve for spray control. This system was fitted into a self-propelled machine with two vertical spray booms. A laboratory test was carried out to evaluate the system limitations (detection range, response time, optimal sensor location); and once the feasibility of the system was known, a field test was conducted. Inside the greenhouse, the same parameters were determined for canopy presence. The system’s capacity to start and stop spraying at the beginnings and ends of the crop lines was also analysed. In addition, the minimum crop line surface with no plant mass that triggers system activation was determined. The results show that the detection range was 0–0.4 m with an average response time of 1.67 s. Based on these parameters, the optimal sensor location was determined for the different forward velocities. In conclusion, the results show that this system is suitable for plant detection at a forward speed of 0.9 m s^?1, allowing growers to stop spraying automatically at the ends of the crop lines and where plant mass absence is greater than 1.0 lineal meter.     

Vineyard zone delineation by cluster classification based on annual grape and vine characteristics

This study describes a method for vineyard zone delineation based on spatial interpolation of data on annual monitoring of grape and vine growth from 2007 to 2012 for four commercial vines (Cabernet Sauvignon, Mencía, Merlot and Tempranillo) located in the Bierzo Denomination of Origen (NW Spain). A sampled grid of 20 × 29 m (14 vines/ha) was defined for each vineyard and data were collected for ten soil, six grape composition, three grape production and five vine vigour variables. Continuous maps of each variable were created by spatial interpolation from the sampled points. Several zone delineations were obtained by clustering—using the iterative self-organizing data analysis (ISODATA) algorithm—according to different combinations of the studied variables. The resulting zone delineations were analysed (ANOVA) in order to determine whether the variables in the two cluster classifications for two or three zones were statistically different from each other. The selected delineation was the cluster that included total soluble solids, titratable acidity, total phenolic content, pH, mean cluster weight and length of the internode in two zones. The results point to the feasibility of this approach to vineyard zone delineation. Further research is necessary to confirm the effectiveness of this approach for other locations and evaluate the usefulness of introducing new grape and vine variables.     

Cloud-based monitoring system for lysimetric and agroclimatic data

The availability of irrigation water is one of the main concerns in Mediterranean agriculture. For this reason, it is so important to accurately determine the water needs of the crop in order to optimize the use of scarce water resources. This paper presents the design and operation validation of an agroclimatic data acquisition system composed of a set of wireless nodes with different functionalities to ascertain irrigation requirements based on weather and lysimetric data. These nodes were based on a common single-board computer to which, depending on the required features, additional hardware components were added. A comparative study of the different single-board computers available in the market was conducted and the Raspberry Pi device was selected due its high performance to cost ratio. With this philosophy, the design of two types of nodes was proposed: climate nodes and lysimetric nodes. Software drivers were developed for both to perform data acquisition and to send the measurements through a mobile network to an application hosted in the cloud. This application managed the storage of the data in a structured-relational database. The required interfaces were programmed to allow the user to view historical and real-time data, as well as configure additional parameters of the nodes related to the crop, geographical location and so on. This cloud application is accessible from any computer or mobile device with an internet connection. All the software tools and hardware platforms were low-cost and open source. Various performance tests were carried out both in the laboratory and in the field, obtaining evapotranspiration measurements consistent with the reference evapotranspiration calculated from data of the climate node.     

Geographical distribution and first molecular detection of an <Emphasis Type="Italic">Emaravirus,High Plains wheat mosaic virus</Emphasis>, in Argentina

High Plains wheat mosaic virus (HPWMoV) has recently been assigned to genus Emaravirus and is the causal agent of High Plains disease. In this work the geographical distribution and first molecular detection of HPWMoV in Argentina are reported. The virus was detected in six provinces and nine hosts, including wheat, corn, oat and barley, as well as weeds, which play an important role in the epidemiology of this disease. Molecular and phylogenetic analyses of a portion of RNA3 nucleoprotein gene sequence showed that five HPWMoV isolates from different wheat growing regions of Argentina were identical, and suggest a single introduction of HPWMoV to this country, possibly through corn seeds. To the best of our knowledge, this is the first molecular detection of HPWMoV in South America. These results highlight the importance of certification of viruses-free cereal seeds and strict controls for material transfer between different countries to prevent the entry not only of new pathogens but also of new variants or strain at sites where the pest has already been detected.     

Contribution of <Emphasis Type="Italic">Rosellinia necatrix</Emphasis> toxins to avocado white root rot

By transversely cutting infected avocado plant stems and using PCR techniques on avocado leaves, two experiments were carried out to determine whether Rosellinia necatrix can invade avocado vascular tissues. We were unable to detect the pathogen in either stems or leaves in either experiment, so we concluded that R. necatrix does not invade the vascular system of the plant. Additionally, the toxins produced by the pathogen were also studied to determine whether such toxins could contribute to the wilting and death of avocado plants infected by R. necatrix, having an effect on avocado leaves, where they can hinder the photosynthetic process. First, we isolated and identified the toxins cytochalasin E and rosnecatrone from filtrates of six R. necatrix isolates. Second, we tried to detect cytochalasin E in sap and leaves from infected avocado plants, and it was not detected at the minimum level of 50 μg/kg in leaves or 25 μg/kg on sap. Finally, we observed changes in fluorescence emitted by the avocado leaf surface (to detect photosynthetic efficiency) after inoculating avocado plants with this toxin. Fluorescence was higher in the leaves of plants immersed in toxin solution after 4 and 8 days, but not after longer periods of time. In this work, we demonstrated that although R. necatrix is not a fungus that invades the vascular system, its toxins are probably involved in the wilting and death of infected avocado plants, decreasing the efficiency of photosynthesis.