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Phytophthora capsici epidemics are propelled by warm temperatures and wet conditions. With temperatures and inland flooding in many locations worldwide expected to rise as a result of global climate change, understanding of population structure can help to inform management of P. capsici in the field and prevent devastating epidemics. Thus, we investigated the effect of host crop, geographical origin, fungicide sensitivity, and mating type on shaping the population structure of P. capsici in the eastern United States. Our fungicide in vitro assays identified the emergence of insensitive isolates for fluopicolide and mefenoxam. A set of 12 microsatellite markers proved informative to assign 157 P. capsici isolates to five distinct genetic clusters. Implementation of Bayesian structure, population differentiation, genetic diversity statistics, and index of association analysis, allowed us to identify population structure by host with some correspondence with genetic clusters for cucumber and squash isolates. We found weak population structure by state for geographically close isolates. In this study, we discovered that North Carolina populations stratify by fluopicolide sensitivity with insensitive isolates experiencing nonrandom mating. Our findings highlight the need for careful monitoring of local field populations, improved selection of relevant isolates for breeding efforts, and hypervigilant surveillance of resistance to different fungicides.

Black rot of sweetpotato, caused by Ceratocystis fimbriata, is an important reemerging disease threatening sweetpotato production in the United States. This study assessed disease susceptibility of the storage root surface, storage root cambium, and slips (vine cuttings) of 48 sweetpotato cultivars, advanced breeding lines, and wild relative accessions. We also characterized the effect of storage root development on susceptibility to C. fimbriata. None of the cultivars examined at the storage root level were resistant, with most cultivars exhibiting similar levels of susceptibility. In storage roots, Jewel and Covington were the least susceptible and significantly different from White Bonita, the most susceptible cultivar. In the slip, significant differences in disease incidence were observed for above- and below-ground plant structures among cultivars, advanced breeding lines, and wild relative accessions. Burgundy and Ipomoea littoralis displayed less below-ground disease incidence compared with NASPOT 8, Sunnyside, and LSU-417, the most susceptible cultivars. Correlation of black rot susceptibility between storage roots and slips was not significant, suggesting that slip assays are not useful to predict resistance in storage roots. Immature, early-developing storage roots were comparatively more susceptible than older, fully developed storage roots. The high significant correlation between the storage root cross-section area and the cross-sectional lesion ratio suggests the presence of an unfavorable environment for C. fimbriata as the storage root develops. Incorporating applications of effective fungicides at transplanting and during early-storage root development when sweetpotato tissues are most susceptible to black rot infection may improve disease management efforts.

In 1922, Phytophthora capsici was described by Leon Hatching Leonian as a new pathogen infecting pepper (Capsicum annuum L.), with disease symptoms of root rot, stem and fruit blight, seed rot, and plant wilting and death. Extensive research has been conducted on P. capsici over the last 100 years. This review succinctly describes the salient mile markers of research on P. capsici with current perspectives on the pathogen’s distribution, economic importance, epidemiology, genetics and genomics, fungicide resistance, host susceptibility, pathogenicity mechanisms, and management.

Phytophthora capsici is an oomycete pathogen causing economically important diseases in a wide range of hosts worldwide including cucurbitaceous, solanaceous, and fabaceous crops. All plant parts, crown and roots, or only the fruit may be affected depending on the host, and symptoms can range from wilting to rot and plant death. Considered a hemibiotroph, P. capsici can be cultured in artificial media and maintained in long-term storage. In this diagnostic guide, we describe methods to identify P. capsici infection based on disease symptoms and pathogen signs. We also outline methods for molecular identification, pathogen isolation, storage of single-sporangium cultures, and pathogenicity testing.

Phytophthora blight, caused by Phytophthora capsici, is an important disease of peppers in the United States and worldwide. P. capsici causes crown, root, and fruit rot as well as foliar lesions in peppers. Field trials were conducted in 2015 and 2016 to evaluate 32 commercial and experimental pepper cultivars against a mixed-isolate inoculum in North Carolina. Cultivars Martha-R and Meeting were classified as highly resistant to P. capsici, and Paladin was classified as resistant. Intermediate resistance to P. capsici in the field was observed with Fabuloso, Revolution, Vanguard, Archimedes, Aristotle, Ebano-R, and Declaration. Greenhouse experiments were conducted to determine the response of 48 pepper cultivars when inoculated individually with two isolates from North Carolina and an isolate from Michigan. Isolates exhibited different levels of virulence in pepper cultivars screened for resistance. Landraces CM334 and Fidel as well as the cultivars Martha-R, Meeting, and Intruder were categorized as highly resistant or resistant to the three isolates tested. Overall, highly resistant cultivars tended to respond similarly to field mix inoculations and greenhouse single isolate inoculations.

La quema de cascarilla de arroz es una práctica frecuente en la preparación de terrenos para una producción a corto plazo de cultivos de hortalizas en el municipio de Villa del Rosario, Norte de Santander, Colombia. Con el objeto de determinar el efecto de esta práctica se realizó un estudio para evaluar el efecto de la quema de cascarilla de arroz en el suelo sobre la población de hongos formadores de micorrizas arbusculares, mediante el recuento de esporas y determinación del porcentaje de colonización por estos hongos en raíces de hortalizas antes y después de la quema durante cuatro períodos de cultivos. Además, se determinó el carbono orgánico, fósforo disponible, nitrógeno y pH del suelo. Se evaluaron dos secuencias de cultivos simultáneas en tres fincas donde se realiza rotación de cultivos y se alterna la producción de diferentes hortalizas con el cultivo de cilantro. Se realizó un análisis de varianza, comparación de medias según la prueba de Tukey y un análisis de componentes principales. Los resultados mostraron un efecto significativo en la reducción de esporas y la colonización de hongos de micorriza arbuscular después de la quema y una recuperación gradual hacia el cuarto cultivo en cada finca. En las variables de pH y carbono orgánico se encontró un aumento en el período inmediatamente después de la quema, con aumento también del contenido de fósforo. El efecto negativo sobre las micorrizas demuestra la necesidad de modificar la utilización de esta práctica en la preparación del suelo con el objeto de conservar la población de esporas de estos hongos y su interacción con las raíces de las plantas cultivadas. The burning of rice husk is an usual practice in land preparation for short-term production of vegetable crops in Villa del Rosario, Norte de Santander, Colombia. To determine the effect of this practice, we calculated the number of mycorrhizal spores and their root colonization percentage in coriander crops before the burning, and during four periods after. Also, organic carbon, available phosphorus, nitrogen, and pH were determined. The study involved two crops sequences on three farms of the zone where crop rotation is practiced and production of different vegetable alternates with coriander. The data was analyzed using Anova and Tukey test, along with an analysis of principal components. A significant effect was observed on the reduction of mycorrhizal fungi spores and root colonization immediately after the burning, and a gradual recovery of both of them was observed towards the fourth cultivation. Organic carbon and pH also increased after the burning, with increases of available phosphorus. The negative effect on mycorrhizal fungi shows the necessity to modify the use of this agricultural practice for land preparation, with the aim to preserve the community of mycorrhizal spores and their interaction with the roots of cultivated plants.