Global Cropland Connectivity: A Risk Factor for Invasion and Saturation by Emerging Pathogens and Pests.

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.

Stacking three late blight resistance genes from wild species directly into African highland potato varieties confers complete field resistance to local blight races.

Considered responsible for one million deaths in Ireland and widespread famine in the European continent during the 1840s, late blight, caused by Phytophthora infestans, remains the most devastating disease of potato (Solanum tuberosum L.) with about 15%-30% annual yield loss in sub-Saharan Africa, affecting mainly smallholder farmers. We show here that the transfer of three resistance (R) genes from wild relatives [RB, Rpi-blb2 from Solanum bulbocastanum and Rpi-vnt1.

Genotyping of Phytophthora infestans in Eastern Africa Reveals a Dominating Invasive European Lineage.

Strains of Phytophthora infestans, the pathogen causing late blight of potato and tomato, are thought to be moved around the world through infected planting material. Since its first appearance in 1941, late blight has caused important losses to potato production in the eastern-Africa region (EAR). In the current study, the genetic structure of the population in Kenya, Uganda, Tanzania, Burundi, and Rwanda was characterized using 12-plex microsatellite markers with the aim of testing the hypothesis that a strain originating from Europe, 2_A1, has recently dominated the population in EAR.

Incomplete Infection of Secondarily Infected Potato Plants - an Environment Dependent Underestimated Mechanism in Plant Virology.

The common assumption in potato virus epidemiology is that all daughter tubers produced by plants coming from infected mother tubers (secondary infection) will become infected via systemic translocation of the virus during growth. We hypothesize that depending on the prevalent environmental conditions, only a portion of the daughter tubers of a plant that is secondarily infected by viruses may become infected. To test this hypothesis experimental data from standardized field experiments were produced in three contrasting environments at 112, 3280, and 4000 m a.

Wide Phenotypic Diversity for Resistance to Phytophthora infestans Found in Potato Landraces from Peru.

The wild and cultivated species of potato have been utilized in potato breeding to good effect but only a very small sample of the available biodiversity has been exploited. In total, 468 accessions of wild and cultivated species of potato were assessed for resistance to the oomycete pathogen Phytophthora infestans using greenhouse assays. Wide phenotypic variation for resistance was found within a species (i.

The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes.

Phytophthora infestans is a destructive plant pathogen best known for causing the disease that triggered the Irish potato famine and remains the most costly potato pathogen to manage worldwide. Identification of P. infestan's elusive center of origin is critical to understanding the mechanisms of repeated global emergence of this pathogen.

Climate change may have limited effect on global risk of potato late blight.

Weather affects the severity of many plant diseases, and climate change is likely to alter the patterns of crop disease severity. Evaluating possible future patterns can help focus crop breeding and disease management research. We examined the global effect of climate change on potato late blight, the disease that caused the Irish potato famine and still is a common potato disease around the world.

Phenotypic stability and genome-wide association study of late blight resistance in potato genotypes adapted to the tropical highlands.

Potato genotypes from a breeding population adapted to tropical highlands were analyzed for the stability of late blight resistance and also for marker-phenotype association. We harmonized the historical evaluation data, consisting of observations spanning 6 years from two field sites utilizing a resistance scale constructed by comparing the area under the disease progress curve (AUDPC) values of 172 genotypes with that of susceptible control 'Yungay'. In total, 70 potato genotypes had a coefficient of variability <0.

Use of Phosphonate to Manage Foliar Potato Late Blight in Developing Countries.

Twenty phosphonate products found in the agrochemical market in Ecuador and Peru were evaluated in bioassays for the control of foliar potato late blight, caused by Phytophthora infestans. Eight phosphonate products were evaluated in 16 field experiments done in Peru, Ecuador, Kenya, and Nepal. A meta-analysis across locations involving 71 combinations of potato genotype by site and year demonstrated a significant relationship between phosphonate application rate and efficacy for controlling late blight on potato foliage.

The plant pathogen Phytophthora andina emerged via hybridization of an unknown Phytophthora species and the Irish potato famine pathogen, P. infestans.

Emerging plant pathogens have largely been a consequence of the movement of pathogens to new geographic regions. Another documented mechanism for the emergence of plant pathogens is hybridization between individuals of different species or subspecies, which may allow rapid evolution and adaptation to new hosts or environments. Hybrid plant pathogens have traditionally been difficult to detect or confirm, but the increasing ease of cloning and sequencing PCR products now makes the identification of species that consistently have genes or alleles with phylogenetically divergent origins relatively straightforward.

Assessing the Adequacy of the Simulation Model LATEBLIGHT Under Nicaraguan Conditions.

In this study, the adequacy of the late blight simulation model LATEBLIGHT (version LB2004) was evaluated under Nicaraguan conditions. During 2007 to 2008, five field experiments were conducted in three potato-production regions in northern Nicaragua. Two susceptible ('Cal White' and 'Granola') and one resistant ('Jacqueline Lee') potato cultivars were evaluated without use of fungicides and with three application intervals (4, 7, and 14 days) of the fungicide chlorothalonil.

Estimating the level of susceptibility to Phytophthora infestans in potato genotypes.

Resistance and susceptibility are closely related terms but differ in their underlying assumptions and measurement. Standardized methods for determining the level of resistance and susceptibility in potato to Phytophthora infestans, the causal agent of late blight, have traditionally been semiquantitative and are not based on a true interval scale, thus making their use in most mathematical and statistical operations inappropriate. Recently, researchers have attempted to develop interval scales using regression analysis of the direct or transformed area under the disease progress curve (AUDPC).

Rainfall Thresholds as Support for Timing Fungicide Applications in the Control of Potato Late Blight in Ecuador and Peru.

Accumulated rainfall thresholds were studied in seven field experiments conducted in Ecuador and Peru for their value in timing applications of fungicide to control potato late blight, caused by Phytophthora infestans. Fungicide regimes based on accumulated rainfall thresholds ranging from 10 to 70 mm were compared with calendar spray schemes of every 5 or 7 days. Very low thresholds of 10 to 20 mm gave similar levels of control and resulted in similar number of sprays as did calendar spraying.

Qualification of a Plant Disease Simulation Model: Performance of the LATEBLIGHT Model Across a Broad Range of Environments.

ABSTRACT The concept of model qualification, i.e., discovering the domain over which a validated model may be properly used, was illustrated with LATEBLIGHT, a mathematical model that simulates the effect of weather, host growth and resistance, and fungicide use on asexual development and growth of Phytophthora infestans on potato foliage.

Simulation of Potato Late Blight in the Andes. II: Validation of the LATEBLIGHT Model.

ABSTRACT LATEBLIGHT, a mathematical model that simulates the effect of weather, host growth and resistance, and fungicide use on asexual development and growth of Phytophthora infestans on potato foliage, was validated for the Andes of Peru. Validation was needed due to recent modifications made to the model, and because the model had not been formally tested outside of New York State. Prior to validation, procedures to estimate the starting time of the epidemic, the amount of initial inoculum, and leaf wetness duration were developed.

Simulation of Potato Late Blight in the Andes. I: Modification and Parameterization of the LATEBLIGHT Model.

ABSTRACT LATEBLIGHT, a mathematical model that simulates the effects of weather, host growth and resistance, and fungicide use on asexual development and growth of Phytophthora infestans on potato foliage, was modified so that it can be used in the Andes and, eventually, worldwide. The modifications included (i) the incorporation of improved equations for the effect of temperature on lesion growth rate (LGR) and sporulation rate (SR); (ii) the incorporation of temperature-dependent latent period (LP); and (iii) the use of experimentally measured parameters of LGR, SR, and LP for specific potato cultivars and pathogen lineages. The model was parameterized for three Peruvian potato cultivars (Tomasa, Yungay, and Amarilis) infected with isolates of a new clonal lineage of P.

Preemergence Infection of Potato Sprouts by Phytophthora infestans in the Highland Tropics of Ecuador.

Experiments were conducted to determine whether preemergence infection of potato sprouts by Phytophthora infestans occurs in the highland tropics of Ecuador. In three separate experiments in the field, P. infestans was identified on the preemerged sprouts of 49, 5, and 43% of tubers, respectively, which had been removed from soil prior to emergence.

Stability in Population of Phytophthora infestans Attacking Tomato in Ecuador Demonstrated by Cellulose Acetate Assessment of Glucose-6-Phosphate Isomerase.

Cellulose acetate electrophoresis was used to examine glucose-6-phosphate (Gpi) isomerase banding patterns of the population of Phytophthora infestans attacking tomato in Ecuador. All but two of 160 sporulating lesions from tomato leaflets collected from 25 tomato fields between January 1998 and March 1999 produced the 86/100 Gpi isozyme electromorph. This isozyme type is characteristic of the US-1 clonal lineage, indicating that no change in the population of P.

A Global Marker Database for Phytophthora infestans.

A marker database was compiled for isolates of the potato and tomato late blight pathogen, Phytophthora infestans, originating from 41 locations which include 31 countries plus 10 regions within Mexico. Presently, the database contains information on 1,776 isolates for one or more of the following markers: restriction fragment length polymorphism (RFLP) "fingerprint" consisting of 23 bands; mating type; dilocus allozyme genotype; mitochondrial DNA haplotype; sensitivity to the fungicide metalaxyl; and virulence. In the database, 305 entries have unique RFLP fingerprints and 258 entries have unique multilocus genotypes based on RFLP fingerprint, dilocus allozyme genotype, and mating type.