During the past two decades, the wheat-producing areas of the Great Plains region in North America experienced frequent, severe yield losses to stripe rust (Puccinia striiformis f. sp. tritici). In general, outbreaks of rust diseases in the Southern Great Plains region often precede disease problems in the Central and Northern Great Plains. However, these generalizations provide little information, and our objective for this study was to identify weather variables, geographical areas, and time periods that influence the early stages of stripe rust epidemics in the Great Plains. Data used in this analysis consisted of monthly summaries of temperature, precipitation, and soil moisture from 10 climate districts in Texas of the United States. These environmental variables were paired with estimates of wheat yield losses to stripe rust in Kansas from 2000 to 2019, with yield loss coded as a binary variable (1 = >4% statewide yield loss). An ensemble of simple models representing weather variables, time periods, and geographical locations were hypothesized to be influential in the development of stripe rust epidemics. Model performance was verified with observations not used in model development. Results of this study indicated that soil moisture within two to three climate districts in Texas were particularly influential in regional disease development. These areas of Texas were 700 to 1,000 km away from locations in Kansas where the disease-related yield losses were observed, and they often preceded disease losses by 3 to 6 months. In the future, these models could help establish priority locations and time periods for disease scouting and inform regional estimates of disease risk.
Abstract CONTEXT Effective seed systems must both distribute high-performing varieties efficiently and slow or stop the spread of pathogens and pests. Epidemics increasingly threaten crops around the world, endangering the incomes and livelihoods of smallholder farmers. Responding to these food and economic security challenges requires stakeholders to act quickly and decisively during the early stages of invasions, typically with very limited resources. The recent introduction of cassava mosaic virus into southeast Asia threatens cassava production in the region. OBJECTIVES Our goal in this study is to provide a decision-support framework for efficient management of healthy seed systems, applied to cassava mosaic disease. The specific objectives are to (1) evaluate disease risk in disease-free parts of Cambodia, Lao PDR, Thailand, and Vietnam by integrating disease occurrence, climate, topology, and land use, using machine learning; (2) incorporate this predicted environmental risk with seed exchange survey data and whitefly spread in the landscape to model epidemic spread in a network meta-population model; and (3) use scenario analysis to identify candidate regions to be prioritized in seed system management. RESULTS AND CONCLUSIONS The analyses allow stakeholders to evaluate strategy options for allocating their resources in the field, guiding the implementation of seed system programs and responses. Fixed rather than adaptive deployment of clean seed produced more favorable outcomes in this model, as did prioritization of a higher number of districts through the deployment of smaller volumes of clean seed. SIGNIFICANCE The decision-support framework presented here can be applied widely to seed systems challenged by the dual goals of distributing seed efficiently and reducing disease risk. Data-driven approaches support evidence-based identification of optimized surveillance and mitigation areas in an iterative fashion, providing guidance early in an epidemic, and revising them as data accrue over time.
ABSTRACT Phytophthora infestans is a fungal-like organism belonging to the Phylum Oomycota, which is currently classified within the Kingdom Stramenopila. This oomycete is the causal agent of potato late blight, and as such, it is believed to be a major contributor to the Potato Famine, which ravaged Ireland in the 1840's. Current annual losses worldwide due to P. infestans gross over $6.8 billion. Interactions between two different isolates of the US-8 race and three potato (Solanum tuberosum) cultivars, and in particular, the effect of temperature on the disease cycle, were analyzed using a Detached Leaf Assay (DLA), under controlled laboratory conditions. Incubation period was variable between conditions and, in general, incubation period was longest for each isolate at low temperatures. For isolate NC092ba, mean incubation period was longest at 12°C and did not vary significantly between cultivars. At 18°C, incubation period also did not vary between cultivars but it was shorter than at 12°C. For leaves infected at 24°C with isolate NC092ba, there was a significant difference in incubation period between cultivars, with Russet Burbank being longest. For leaves infected with isolate PSUPotb, incubation period was again longest at 12°C and there was no significant difference between cultivars. At 18°C and 24°C, incubation period was longer for Russet Burbank than for Kennebec or Red Norland. Furthermore, disease progress over time was more severe at higher temperatures for each isolate, across cultivars. Confirmation of pathogen presence in infected leaf tissue was successfully obtained using previously developed P. infestans specific primers in a standard Polymerase Chain Reaction (PCR) assay.
The data includes national surveys of 15 districts in Vietnam and 16 districts in Cambodia, with 15 responses by district. Districts were selected based on high cassava production density and expert input from local government officials. National surveys covered the following themes: (a) respondent information, (b) seed use overview, and (c) field and household data. In addition to the aforementioned categories, the subnational surveys collected data on (d) quality, (e) affordability/profitability, and (f) information sources.
The geographic pattern of cropland is an important risk factor for invasion and saturation by crop-specific pathogens and arthropods. Understanding cropland networks supports smart pest sampling and mitigation strategies. We evaluate global networks of cropland connectivity for key vegetatively propagated crops (banana and plantain, cassava, potato, sweet potato, and yam) important for food security in the tropics. For each crop, potential movement between geographic location pairs was evaluated using a gravity model, with associated uncertainty quantification. The highly linked hub and bridge locations in cropland connectivity risk maps are likely priorities for surveillance and management, and for tracing intraregion movement of pathogens and pests. Important locations are identified beyond those locations that simply have high crop density. Cropland connectivity risk maps provide a new risk component for integration with other factors-such as climatic suitability, genetic resistance, and global trade routes-to inform pest risk assessment and mitigation.
Anonymized responses of the questionnaire respondents in Cambodia (Battambang n=100, Ratanakiri n=100) and Vietnam (Tay Ninh n=100, Dak Lak n=94), respectively
Climate change is a challenge for plant pathologists and will likely affect their work in providing management tools for disease. The new emphasis on the availability of data in agriculture can help develop adaptation strategies for a community of practice in plant pathology. The authors also explore how countries such as Haiti can address their goals for improving infrastructure and production and the livelihoods of smallholder farmers as they navigate climate change adaptations.