Afternoon Ascospore Release in Claviceps purpurea Optimizes Perennial Ryegrass Infection

In Kentucky bluegrass (Poa pratensis), Claviceps purpurea, the causal agent of ergot, typically releases ascospores during the early-morning hours, between about midnight and 10:00 A.M., corresponding to time of flowering, when the unfertilized ovaries are most susceptible to infection. During aeromycology studies of C. purpurea in perennial ryegrass (Lolium perenne) in northeastern Oregon during 2008 to 2010 and 2013, a strain of C. purpurea was found that released ascospores in the afternoon, coinciding with flowering in perernrial ryegrass. Under controlled environmental conditions, sclerotia from perennial ryegrass and Kentucky bluegrass released spores in the afternoon and morning, respectively, consistent with tirning of spore release under field conditions. Internal transcribed spacer (ITS) sequences of single sclerotial isolates from Kentucky bluegrass and perennial ryegrass were consistent with C. putpurea, although minor variations in ITS sequences among isolates were noted. Differences between Kentucky bluegrass and perennial ryegrass isolates were observed in random amplified polymorphic DNA. Evidence is provided for adaptation of C. purpurea to perennial ryegrass by means of delayed spore release that coincides with afternoon flowering in perennial ryegrass

Trachoma in Viet Nam: results of 11 surveillance surveys conducted with the Global Trachoma Mapping Project.

PURPOSE: Following interventions against trachoma in Viet Nam, impact surveys conducted in 2003-2011 suggested that trachoma was no longer a public health problem. In 2014, we undertook surveillance surveys to estimate prevalence of trachomatous inflammation-follicular (TF) and trichiasis. METHODS: A population-based prevalence survey was undertaken in 11 evaluation units (EUs) encompassing 24 districts, using Global Trachoma Mapping Project methods. A two-stage cluster sampling design was used in each EU, whereby 20 clusters and 60 children per cluster were sampled. Consenting eligible participants (children aged 1-9 years and adults aged ≥50 years) were examined for trachoma. RESULTS: A total of 9391 households were surveyed, and 20,185 participants (98.8% of those enumerated) were examined for trachoma. EU-level TF prevalence in 1-9-year-olds ranged from 0% to 1.6%. In one cluster (in Hà Giang Province), the percentage of children with TF was 10.3%. The overall pattern of cluster-level percentages of children with TF, however, was consistent with an exponential distribution, which would be consistent with trachoma disappearing. Among people aged ≥50 years, prevalence of trichiasis by EU ranged from 0% to 0.75%; these estimates are equivalent to 0-0.13% in all ages. The prevalence of trichiasis unknown to the health system among people aged ≥50 years, by EU, ranged from 0% to 0.17%, which is equivalent to 0-0.03% in all ages. CONCLUSION: Findings suggest that trachoma is no longer a public health problem in any of the 11 EUs surveyed. However, given the high proportion of children with TF in one cluster in Hà Giang Province, further investigations will be undertaken

Population Biology of Verticillium dahliae in Potato and Mint

Verticillium dahliae (Vd) causes Verticillium wilt of potato and mint and both crops can be rotated in the same fields of the Columbia Basin in the Pacific Northwest. Inoculum of Vd can be found in dirt associated with certified potato seed which is imported and planted on a large scale. The incidence and impact of Vd in dirt associated with certified seed tubers on Verticillium wilt and yield was quantified. Most seed lots contained Vd-infested dirt on seed tubers (68%) and in loose dirt associated with seed lot transport (82%). High Vd levels in seed tuber dirt resulted in greater stem sap colonization when Vd levels in field soil was low (PP=0.04). Infested dirt on seed tubers may introduce Vd into production fields and long-term management requires reducing these propagules.Isolates of Vd from mint and potato usually belong to different vegetative compatibility groups (VCGs) which may restrict gene flow and cause genetic differentiation between populations infecting these hosts. Mating-types and microsatellite haplotypes were determined for 286 Vd isolates from mint, potato, and other hosts and substrates. All potato and mint isolates possessed MAT1-2. Genotypic diversity was significantly greater among potato compared to mint isolates. Isolates from mint and potato were significantly genetically diverged. Significant genetic differentiation was not observed between VCG4A and 4B from potato. Overall, Vd populations from mint and potato fit a clonal reproduction model and populations from these hosts are genetically distinct.Potato early dying (PED) can be caused by Vd and pectolytic bacteria in the genus Pectobacterium, which can also cause aerial stem rot of potato. Additive or synergistic interactions between Vd and Pectobacterium may increase disease severity. Symptoms were evaluated in the greenhouse and pathogens were quantified in stems using real-time PCR. PED symptoms caused by P. carotovorum subsp. carotovorum isolate Ec101 or Vd alone were similar. Inoculations with P. wasabiae isolate PwO405 caused aerial stem rot symptoms and high levels of bacteria were observed in stems. Additive or synergistic effects were not observed in plants co-inoculated with Vd and either Pectobacterium isolate

Population biology of Verticillium dahliae in potato and mint

Verticillium dahliae (Vd) causes Verticillium wilt of potato and mint and both crops can be rotated in the same fields of the Columbia Basin in the Pacific Northwest. Inoculum of Vd can be found in dirt associated with certified potato seed which is imported and planted on a large scale. The incidence and impact of Vd in dirt associated with certified seed tubers on Verticillium wilt and yield was quantified. Most seed lots contained Vd-infested dirt on seed tubers (68%) and in loose dirt associated with seed lot transport (82%). High Vd levels in seed tuber dirt resulted in greater stem sap colonization when Vd levels in field soil was low (P<0.01) and resulted in greater pathogen levels in postharvest field soils (P=0.04). Infested dirt on seed tubers may introduce Vd into production fields and long-term management requires reducing these propagules. Isolates of Vd from mint and potato usually belong to different vegetative compatibility groups (VCGs) which may restrict gene flow and cause genetic differentiation between populations infecting these hosts. Mating-types and microsatellite haplotypes were determined for 286 Vd isolates from mint, potato, and other hosts and substrates. All potato and mint isolates possessed MAT1-2. Genotypic diversity was significantly greater among potato compared to mint isolates. Isolates from mint and potato were significantly genetically diverged. Significant genetic differentiation was not observed between VCG4A and 4B from potato. Overall, Vd populations from mint and potato fit a clonal reproduction model and populations from these hosts are genetically distinct. Potato early dying (PED) can be caused by Vd and pectolytic bacteria in the genus Pectobacterium, which can also cause aerial stem rot of potato. Additive or synergistic interactions between Vd and Pectobacterium may increase disease severity. Symptoms were evaluated in the greenhouse and pathogens were quantified in stems using real-time PCR. PED symptoms caused by P. carotovorum subsp. carotovorum isolate Ec101 or Vd alone were similar. Inoculations with P. wasabiae isolate PwO405 caused aerial stem rot symptoms and high levels of bacteria were observed in stems. Additive or synergistic effects were not observed in plants co-inoculated with Vd and either Pectobacterium isolate

Relative roles of tuber- and soilborne inoculum in verticillium wilt of potato and quantification of resistance in mint

Inoculum of Verticillium dahliae, causal agent of Verticillium wilt (VW) of potato, exists as soilborne microsclerotia, however, it can also be found in vascular tissue of seed tubers. The effects of intratuber inoculum on VW symptoms were measured in the greenhouse and in fields with and without prior potato rotations. Vascular infection of seed tubers did not result in significant disease symptoms, stem colonization, microsclerotia production or progeny tuber infection in the greenhouse. The incidence of V. dahliae infection in seed lots was not related to differences in yield, symptom severity or progeny tuber infection in field experiments, however, disease incidence and severity were higher in common potato rotation fields compared to long rotation fields. Results indicate that efforts to reduce primary inoculum should focus on reducing pathogen populations in the soil. Verticillium wilt is also a major constraint to mint (Mentha) production. The use of resistant cultivars is an important component of VW management and Agrobacterium-mediated transformation provides the opportunity to improve existing mint cultivars. Several M. arvensis and M. longifolia selections were evaluated for resistance to V. dahliae isolates from different hosts and vegetative compatibility groups (VCGs) in the greenhouse. Transgenic peppermint (M. x piperita) plants containing VW resistance-like sequences cloned from M. longifolia were also evaluated for resistance. V. dahliae isolates from peppermint caused significantly higher disease severity, yield reductions and plant mortality than isolates from other hosts, regardless of VCG. These data supports previous studies indicating host specificity in mint isolates of V. dahliae and suggest host origin may be a better indicator of isolate aggressiveness than VCG. Inoculations of M. arvensis and M. longifolia resulted in necrosis of the inoculated stems, however both species displayed the ability to recover from rhizomes. Both M. arvensis cultivars exhibited relatively low disease symptoms, aboveground stem colonization, yield reductions and plant mortality over repeated periods of cutback and regrowth. Transgenic peppermints containing VW resistance-like sequences did not display resistance to V. dahliae. Results indicate that the restriction of pathogen movement in aboveground stems and the ability to recover from infection may be important characteristics of VW resistance in mint

Evaluation of Bait Crops for the Integrated Management of White Rot (Sclerotium Cepivorum) in Allium Crops

White rot, caused by Sclerotium cepivorum, is a serious disease that causes significant yield losses in Allium production. The pathogen persists in soil as sclerotia, which germinate in response to sulfur compounds in Allium root exudates. This study was aimed at investigating the potential of early-terminated Allium bait crops to reduce densities of S. cepivorum sclerotia in soil. In growth chamber experiments with white onion (A. cepa cv. ‘Southport White Globe’), red onion (A. cepa cv. ‘Marenge’), sweet onion (A. cepa cv. ‘Walla Walla’), and bunching onion (A. fistulosum cv. ‘Parade’), termination of all four Alliums at the first and second leaf stages reduced soil sclerotia populations by up to 62% and 76%, respectively. Examination of soil samples collected four weeks after crop termination indicated that sclerotia populations in bait crop treatments remained low when seedlings were terminated at the first and second leaf stages. In contrast, crop termination at the third leaf stage resulted in an increase in sclerotia counts due to the pathogen reproduction on the bait crops. The reduction in sclerotia populations in soil due to early crop termination was also observed in replicated field trials. Greater reductions in sclerotia counts were observed when plants in these experiments were terminated chemically as opposed to mechanically. In-furrow fungicides did not reduce sclerotia numbers under the conditions tested. This study demonstrates the potential for early termination of Allium bait crops to help reduce white rot inoculum in soil

Verticillium Wilt of Skullcap and Potential for Pathogen Dissemination via Seeds and Stems

A commercial skullcap (Scutellaria lateriflora, family Lamiaceae) crop with wilted and necrotic plants was examined in Washington State in 2008. Three fungal isolates were obtained and identified as Verticillium dahliae based on morphology and sequencing of the internal transcribed spacer DNA region. All three skullcap isolates caused typical Verticillium wilt symptoms on skullcap and two peppermint cultivars. Inoculations of skullcap with the V. dahliae isolates from skullcap and an isolate from peppermint resulted in severe symptoms and a 21 to 78% reduction in aboveground biomass. Isolates from skullcap caused severe symptoms on the susceptible peppermint ‘Black Mitcham’ and reduced yield by up to 82%. One skullcap isolate caused severe symptoms on the moderately resistant ‘Redefined Murray’ in three of four trials and reduced biomass up to 71% compared with noninoculated control plants. The pathogen was recovered from 43 to 69% of skullcap stems from plants inoculated with skullcap or peppermint isolates, and was isolated from 2.5% of seed harvested from skullcap plants inoculated with the peppermint isolate of V. dahliae. This is the first report of V. dahliae infecting skullcap, and the first demonstration of V. dahliae isolates from skullcap and peppermint causing symptoms on both hosts, as well as the seedborne nature of V. dahliae in skullcap

Evidence of a trans-kingdom plant disease complex between a fungus and plant-parasitic nematodes.

Disease prediction tools improve management efforts for many plant diseases. Prediction and downstream prevention demand information about disease etiology, which can be complicated for some diseases, like those caused by soilborne microorganisms. Fortunately, the availability of machine learning methods has enabled researchers to elucidate complex relationships between hosts and pathogens without invoking difficult-to-satisfy assumptions. The etiology of a destructive plant disease, Verticillium wilt of mint, caused by the fungus Verticillium dahliae was reevaluated with several supervised machine learning methods. Specifically, the objective of this research was to identify drivers of wilt in commercial mint fields, describe the relationships between these drivers, and predict wilt. Soil samples were collected from commercial mint fields. Wilt foci, V. dahliae, and plant-parasitic nematodes that can exacerbate wilt were quantified. Multiple linear regression, a generalized additive model, random forest, and an artificial neural network were fit to the data, validated with 10-fold cross-validation, and measures of explanatory and predictive performance were compared. All models selected nematodes within the genus Pratylenchus as the most important predictor of wilt. The fungus after which this disease is named, V. dahliae, was the fourth most important predictor of wilt, after crop age and cultivar. All models explained around 50% of the total variation (R2 ≤ 0.46), and exhibited comparable predictive error (RMSE ≤ 1.21). Collectively, these models revealed that the quantitative relationships between two pathogens, mint cultivars and age are required to explain wilt. The ascendance of Pratylenchus spp. in predicting symptoms of a disease assumed to primarily be caused by V. dahliae exposes the underestimated contribution of these nematodes to wilt. This research provides a foundation on which predictive forecasting tools can be developed for mint growers and reminds us of the lessons that can be learned by revisiting assumptions about disease etiology