Transmission of Spinach Downy Mildew via Seed and Infested Leaf Debris.

Spinach downy mildew, caused by the obligate oomycete pathogen , is a worldwide constraint on spinach production. The role of airborne sporangia in the disease cycle of is well established, but the role of the sexual oospores in the epidemiology of is less clear and has been a major challenge to examine experimentally. To evaluate seed transmission of spinach downy mildew via oospores in this study, isolated glass chambers were employed in two independent experiments to grow out oospore-infested spinach seed and noninfested seeds mixed with oospore-infested crop debris.

The Impatiens Downy Mildew Epidemic in the United States Is Caused by New, Introgressed Lineages of with Prominent Genotypic Diversity and High Evolutionary Potential.

Impatiens downy mildew (IDM) caused by is currently the primary constraint on the production and use of impatiens () as bedding plants worldwide. Downy mildew has been documented since the 1880s from wild-grown spp. but epidemic outbreaks of the disease affecting the commercially grown, ornamental were only reported for the first time in 2003 in the United Kingdom and in 2004 in the United States.

First Report of Powdery Mildew of American Ginseng Caused by in Tennessee and the United States.

American ginseng ( L.), native to the forested regions of northeast U.S is a perennial herb valued as traditional Chinese medicine.

Impact of Calonectria Diseases on Ornamental Horticulture: Diagnosis and Control Strategies.

Diseases caused by fungi in the genus pose a significant threat to the ornamental horticulture industries in Europe and the United States. spp. are particularly challenging pathogens to manage in ornamental production systems and the urban landscape for multiple reasons.

Comparative analysis of extracellular proteomes reveals putative effectors of the boxwood blight pathogens, Calonectria henricotiae and C. pseudonaviculata.

Calonectria henricotiae (Che) and C. pseudonaviculata (Cps) are destructive fungal pathogens causing boxwood blight, a persistent threat to horticultural production, landscape industries, established gardens, and native ecosystems. Although extracellular proteins including effectors produced by fungal pathogens are known to play a fundamental role in pathogenesis, the composition of Che and Cps extracellular proteins has not been examined.

First report: Co-infection of (sweetbox) by and causes a foliar disease of sweetbox in Pennsylvania.

Sweetbox () are high value ornamental shrubs susceptible to disease caused by () and () (Malapi-Wight et al. 2016; Salgado-Salazar et al. 2019).

One Clonal Lineage of Is Primarily Responsible for the Boxwood Blight Epidemic in the United States.

Boxwood blight caused by and is destroying cultivated and native boxwood worldwide, with profound negative economic impacts on the horticulture industry. First documented in the United States in 2011, the disease has now occurred in 30 states. Previous research showed that global populations prior to 2014 had a clonal structure, and only the idiomorph was observed.

The oospore stage of , impatiens downy mildew.

Impatiens downy mildew is caused by , a pathogen known in the United States for over a hundred years, but newly attacking ornamental in production and in the landscape. Little is known about the life cycle of ; thus, in this study an attempt was made to determine whether the pathogen is homothallic or heterothallic. Fourteen single-sporangium isolates and three single-zoospore isolates were used in single and dual inoculations of stem tissue to see whether the pathogen was homothallic or heterothallic; all isolates tested were able to produce oospores when inoculated singly, suggesting homothally.

Spinach Downy Mildew: Advances in Our Understanding of the Disease Cycle and Prospects for Disease Management.

Downy mildew on spinach is caused by , an oomycete pathogen that poses a challenge to spinach production worldwide, especially in organic production. Following infection, produces abundant amounts of asexual sporangia. Sporangia become windborne and initiate new infections locally or distantly, leading to widespread epidemics.

Thermal sensitivity of Calonectria henricotiae and Calonectria pseudonaviculata conidia and microsclerotia.

Knowledge of the thermal sensitivity of conidia and microsclerotia is useful for developing plant disease management approaches that deploy heat to inactivate infectious vegetative propagules of fungal pathogens. For boxwood blight disease, heat treatment of cuttings that harbor conidia and microsclerotia would provide a useful management tool for suppressing the pathogenic activity of Calonectria pseudonaviculata (present in the United States) and C. henricotiae (a quarantine pathogen not present in the United States).

The Effect of Different Temperatures and Moisture Levels on Survival of Calonectria pseudonaviculata in Boxwood Leaves and Twigs and as Microsclerotia Produced in Culture.

Leaves and twig sections of boxwood infected with Calonectria pseudonaviculata were incubated in sand at two moisture levels (36% [carrying capacity] and 5% water [vol/vol]) and at five temperatures (-10, 0, 10, 20, and 30°C). Percent sporulation from monthly tissue samples plated on glucose yeast-extract tyrosine media declined to zero after 5 months at 30°C and after 7 months at -10°C. At 0, 10, and 20°C, sporulation was observed through 30 months.

Pyracantha 'Mohave' Fruit Infection by Phytophthora ramorum and Transmission of the Pathogen from Infected Fruit to Roots of Viburnum tinus.

Colonization of the fleshy fruit of Cornus florida, C. kousa, Laurus nobilis, Malus hupehensis, and Pyracantha 'Mohave' was observed following inoculation with sporangia of Phytophthora ramorum. However, abundant production of chlamydospores was only observed in the fruit of Pyracantha 'Mohave'.

Susceptibility of Some Common Container Weeds to Phytophthora ramorum.

Phytophthora ramorum is known to infect a number of ornamental plants grown in containerized culture. However, pots may also contain weeds. In this research, the foliage of 14 common weeds of containerized plant culture was inoculated with P.

A test system to quantify inoculum in runoff from Phytophthora ramorum-infected plant roots.

Foliar hosts of Phytophthora ramorum are often susceptible to root infection but the epidemiological significance of such infections is unknown. A standardized test system was developed to quantify inoculum in runoff from root-infected Viburnum tinus ?Spring Bouquet? or Rhododendron ?Cunningham's White? cuttings. Cuttings of both species gave off a maximum amount of inoculum 1 to 3 weeks after inoculation.

Standardizing the nomenclature for clonal lineages of the sudden oak death pathogen, Phytophthora ramorum.

Phytophthora ramorum, the causal agent of sudden oak death and ramorum blight, is known to exist as three distinct clonal lineages which can only be distinguished by performing molecular marker-based analyses. However, in the recent literature there exists no consensus on naming of these lineages. Here we propose a system for naming clonal lineages of P.

Propagule Production by Phytophthora ramorum on Lilac (Syringa vulgaris) Leaf Tissue Left on the Surface of Potting Mix in Nursery Pots.

Lilac leaf tissue infected with Phytophthora ramorum was placed on top of potting mix in pots and exposed to different watering regimes or different temperatures to determine if it could serve as a source of inoculum. If pieces of infected leaf were placed in pots containing healthy lilac plants kept under constantly moist conditions or under twice-a-day trickle irrigation for 1 month, inoculum production from infected tissue declined for the first 4 days but declined significantly less steeply under constantly moist conditions. At the end of the experiment, 28% of plants exposed to moist conditions developed root infections, whereas only 6% exposed to trickle irrigation did.

Persistence of Phytophthora ramorum in Soil Mix and Roots of Nursery Ornamentals.

Although most Phytophthora species have a soilborne phase that is crucial for infection of roots and for survival away from the host, the details of the soil phase of Phytophthora ramorum are not yet fully understood. As mycelium ages, it becomes resistant to sterilization by acidic electrolyzed water (AEW), a product of the electrolysis which can be used as a disinfectant. Colonies of P.

Resistance to Triadimefon and Benomyl: Dynamics and Impact on Managing Cucurbit Powdery Mildew.

Frequency of fungicide-resistant strains of Podosphaera xanthii on pumpkins in New York before treatment varied from 3 to 80% for the demethylation inhibiting (DMI) fungicide triadimefon and from 0 to 48% for the benzimidazole fungicide benomyl between 1993 and 1996. When the initial frequency of triadimefon-resistant strains was less than 55%, one application of triadimefon plus chlorothalonil was effective. This application was made after reaching the action threshold of one leaf with powdery mildew symptoms per 50 old leaves (defined as the oldest third of the foliage).