Disaster plant pathology: Smart solutions for threats to global plant health from natural and human-driven disasters.

Disaster plant pathology addresses how natural and human-driven disasters impact plant diseases, and the requirements for smart management solutions. Local to global drivers of plant disease change in response to disasters, often creating environments more conducive to plant disease. Most disasters have indirect effects on plant health through factors such as disrupted supply chains and damaged infrastructure. There is also the potential for direct effects from disasters, such as pathogen or vector dispersal due to floods, hurricanes, and human migration driven by war. Pulse stressors such as hurricanes and war require rapid responses, while press stressors such as climate change leave more time for management adaptation but may ultimately cause broader challenges. Smart solutions for the effects of disasters can be deployed through digital agriculture and decision support systems supporting disaster preparedness and optimized humanitarian aid across scales. Here we use the disaster plant pathology framework to synthesize the effects of disasters in plant pathology and outline solutions to maintain food security and plant health in catastrophic scenarios. We recommend actions for improving food security before and following disasters, including (1) strengthening regional and global cooperation, (2) capacity building for rapid implementation of new technologies, (3) effective clean seed systems that can act quickly to replace seed lost in disasters, (4) resilient biosecurity infrastructure and risk assessment ready for rapid implementation, and (5) decision support systems that can adapt rapidly to unexpected scenarios.

Tree canopy cover and elevation affect the distribution of red harvester ant nests in a peri-urban setting.

With an increase in human population over the past 30 years, regional land use in south Texas has shifted from grassland and shrubland to a peri-urban matrix. Despite this shift from natural areas to more anthropogenically modified habitats, native red harvester ants (Pogonomyrmex barbatus) have maintained nest sites within parts of these matrices. To determine which habitat characteristics in a peri-urban landscape may play a role in red harvester ant nest site selection, we mapped the location of nests in 2020 and 2021. We then evaluated nest presence and absence relative to elevation, percentage of surrounding impervious surfaces, distance to roadways, and tree canopy cover (using NDVI). For a sub-sample of the study site, we also measured soil moisture and estimated the potential foraging area per colony with Voronoi tessellation. We found that nests were clustered together near high human-use areas such as athletic fields, lawns, sidewalks, and railroad tracks. Nests were more likely to be found in areas with higher elevation and lower tree canopy cover, with no impact from surrounding impervious surfaces or soil moisture. In fact, many nests were observed immediately adjacent to roadways and in paved parking lots. Red harvester ants are highly adept at nesting in disturbed, urbanized matrices, but still appear to be constrained by certain environmental factors like shading, potential flood risk (elevation), and access to food resources (foraging area).

Characterization of Pathogen Airborne Inoculum Density by Information Theoretic Analysis of Spore Trap Time Series Data.

In a previous study, air sampling using vortex air samplers combined with species-specific amplification of pathogen DNA was carried out over two years in four or five locations in the Salinas Valley of California. The resulting time series data for the abundance of pathogen DNA trapped per day displayed complex dynamics with features of both deterministic (chaotic) and stochastic uncertainty. Methods of nonlinear time series analysis developed for the reconstruction of low dimensional attractors provided new insights into the complexity of pathogen abundance data. In particular, the analyses suggested that the length of time series data that it is practical or cost-effective to collect may limit the ability to definitively classify the uncertainty in the data. Over the two years of the study, five location/year combinations were classified as having stochastic linear dynamics and four were not. Calculation of entropy values for either the number of pathogen DNA copies or for a binary string indicating whether the pathogen abundance data were increasing revealed (1) some robust differences in the dynamics between seasons that were not obvious in the time series data themselves and (2) that the series were almost all at their theoretical maximum entropy value when considered from the simple perspective of whether instantaneous change along the sequence was positive.

Imidacloprid Movement into Fungal Conidia Is Lethal to Mycophagous Beetles.

Applications of systemic pesticides can have unexpected direct and indirect effects on nontarget organisms, producing ecosystem-level impacts. We investigated whether a systemic insecticide (imidacloprid) could be absorbed by a plant pathogenic fungus infecting treated plants and whether the absorbed levels were high enough to have detrimental effects on the survival of a mycophagous beetle. Beetle larvae fed on these fungi were used to assess the survival effects of powdery mildew and imidacloprid in a factorial design. Fungal conidia were collected from treated and untreated plants and were tested for the presence and concentration of imidacloprid. The survival of beetles fed powdery mildew from imidacloprid-treated leaves was significantly lower than that of the beetles from all other treatments. Imidacloprid accumulated in fungal conidia and hyphae was detected at levels considered lethal to other insects, including coccinellid beetles. Water-soluble systemic insecticides may disrupt mycophagous insects as well as other nontarget organisms, with significant implications for biodiversity and ecosystem function.

Multiple origins of downy mildews and mito-nuclear discordance within the paraphyletic genus Phytophthora.

Phylogenetic relationships between thirteen species of downy mildew and 103 species of Phytophthora (plant-pathogenic oomycetes) were investigated with two nuclear and four mitochondrial loci, using several likelihood-based approaches. Three Phytophthora taxa and all downy mildew taxa were excluded from the previously recognized subgeneric clades of Phytophthora, though all were strongly supported within the paraphyletic genus. Downy mildews appear to be polyphyletic, with graminicolous downy mildews (GDM), brassicolous downy mildews (BDM) and downy mildews with colored conidia (DMCC) forming a clade with the previously unplaced Phytophthora taxon totara; downy mildews with pyriform haustoria (DMPH) were placed in their own clade with affinities to the obligate biotrophic P. cyperi. Results suggest the recognition of four additional clades within Phytophthora, but few relationships between clades could be resolved. Trees containing all twenty extant downy mildew genera were produced by adding partial coverage of seventeen additional downy mildew taxa; these trees supported the monophyly of the BDMs, DMCCs and DMPHs but suggested that the GDMs are paraphyletic in respect to the BDMs or polyphyletic. Incongruence between nuclear-only and mitochondrial-only trees suggests introgression may have occurred between several clades, particularly those containing biotrophs, questioning whether obligate biotrophic parasitism and other traits with polyphyletic distributions arose independently or were horizontally transferred. Phylogenetic approaches may be limited in their ability to resolve some of the complex relationships between the "subgeneric" clades of Phytophthora, which include twenty downy mildew genera and hundreds of species.