Detection of oomycide-insensitive Phytophthora isolates in Maryland ornamental nurseries and Mid-Atlantic landscapes provide data for reconsidering management strategies

2021 ◽  
Author(s):  
Justine Beaulieu ◽  
Johanna Del Castillo Munera ◽  
Yilmaz Balci
Keyword(s):  
Growth Rate ◽  
Mycelial Growth ◽  
Management Strategies ◽  
Resistance Management ◽  
Phytophthora Species ◽  
Oak Forests ◽  
Relative Growth ◽  
Off Label ◽  
Potting Media ◽  
Almost All

Five Phytophthora species comprising a total of 243 isolates (77 P. cinnamomi, 23 P. citrophthora, 18 P. multivora, 18 P. pini, and 107 P. plurivora) were screened for sensitivity to mefenoxam, fosetyl-Al, dimethomorph, dimethomorph + ametoctradin and fluoxastrobin using amended agar assays. Mefenoxam-insensitive isolates were detected within P. cinnamomi (4%), P. multivora (11%), and P. plurivora (12%) even at approximately 2.5x the recommended label rate. These isolates were also insensitive to higher (off-label) concentrations of fluoxastrobin. Concentrations of dimethomorph (400 g/mL) and dimethomorph + ametoctradin (100 g/mL) were mostly effective in mycelial growth inhibition, but two P. plurivora isolates were insensitive, suggesting that resistance management is required. All mefenoxam-insensitive isolates were sensitive to fosetyl-Al at the label rate. Surprisingly, the populations of P. cinnamomi from mid-Atlantic oak forests included insensitive isolates. With almost all species, isolates recovered from asymptomatic hosts (e.g., soil/potting media collected of randomly selected asymptomatic hosts) had a significantly greater relative growth rate when compared to isolates recovered from symptomatic hosts (e.g., isolates recovered from lesions or wilted plants). These findings suggest that mefenoxam should no longer be used to manage oomycetes in Maryland ornamental nurseries and that the use of fluoxastrobin should be limited.

scholarly journals Morphological and Pathogenic Characterization of Sclerotium rolfsii, the Causal Agent of Southern Blight Disease on Common Bean in Uganda

Plant Disease ◽  
2020 ◽  
Vol 104 (8) ◽  
pp. 2130-2137
Author(s):  
Pamela Paparu ◽  
Amos Acur ◽  
Fred Kato ◽  
Catherine Acam ◽  
Justine Nakibuule ◽  
...  
Keyword(s):  
Growth Rate ◽  
Common Bean ◽  
Mycelial Growth ◽  
Smallholder Farmers ◽  
Management Strategies ◽  
Sclerotium Rolfsii ◽  
Southern Blight ◽  
Root Rots ◽  
Mycelial Growth Rate ◽  
Agroecological Zones

Over the last 5 years, Southern blight caused by Sclerotium rolfsii Sacc. has superseded root rots caused by pathogens such as Fusarium and Pythium spp. as a major constraint of common bean (Phaseolus vulgaris L.) production in Uganda. Although S. rolfsii is prevalent in all bean-growing regions of Uganda, there is a lack of information about its diversity and pathogenicity to guide the development of effective management strategies. In total, 348 S. rolfsii isolates were obtained from bean fields in seven agroecological zones of Uganda, with the following objectives: to characterize their morphology, based on mycelial growth rate, mycelium texture, and number of sclerotia; and to determine the pathogenicity of 75 selected isolates on five common bean varieties in artificially inoculated soils in a screenhouse. We found that mycelial growth rate and the number of sclerotia produced on artificial media varied among agroecological zones but not within a zone. The five bean varieties tested were found to be susceptible to S. rolfsii, including varieties MLB49-89A and RWR719 that are resistant to Fusarium and Pythium root rots, respectively. Preemergence damping-off ranged between 0 and 100%, and disease severity index ranged between 4.4 and 100%. The widespread and high levels of S. rolfsii virulence on varieties of common bean indicate that management intervention is urgently required to help reduce losses incurred by Ugandan smallholder farmers. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

scholarly journals Effects of Propamocarb Hydrochloride on Mycelial Growth, Sporulation, and Infection by Phytophthora nicotianae Isolates from Virginia Nurseries

Plant Disease ◽  
2007 ◽  
Vol 91 (4) ◽  
pp. 414-420 ◽  
Author(s):  
Jiahuai Hu ◽  
Chuanxue Hong ◽  
Erik L. Stromberg ◽  
Gary W. Moorman
Keyword(s):  
Mycelial Growth ◽  
Ornamental Plants ◽  
Phytophthora Species ◽  
Phytophthora Nicotianae ◽  
Growth Stages ◽  
Systemic Fungicide ◽  
Reliable Measurement ◽  
Relative Growth ◽  
Sensitive Isolate ◽  
Different Growth Stages

Propamocarb hydrochloride is a systemic fungicide commonly used for control of Phytophthora diseases of nursery crops. Here we report on the effect of this compound on different growth stages of Phytophthora nicotianae, a major pathogen of numerous herbaceous and some woody ornamental plants. A total of 71 isolates were assayed for sensitivity to propamocarb at two concentrations of 1.8 mg/ml (label rate) and 10 mg/ml using clarified V8 agar as a base medium. All isolates grew at 10 mg/ml with the most sensitive isolate having 34.8% relative growth compared with growth on nonamended medium. Nine isolates were selected and further tested for mycelial growth at 0, 1, 10, 25, 50, and 100 mg/ml, and for sporangium production, zoospore motility, and germination at 0, 5, 50, 500, 5,000, and 50,000 μg/ml. EC50 values ranged from 2.2 to 90.1 mg/ml for mycelial growth, 133.8 to 481.3 μg/ml for sporangium production, 88.1 to 249.8 μg/ml for zoospore motility, and 1.9 to 184.6 μg/ml for zoospore germination, respectively. In addition, 17 selected isolates were evaluated for propamocarb sensitivity on Pelargonium × hortorum cv. White Orbit. Two days after seedlings were treated with propamocarb at 3.6 mg/ml, they were inoculated by either inverting one 5-mm-diameter plug of a 3-day-old culture or applying a 10-μl drop containing 20 zoospores onto each cotyledon. Propamocarb hydrochloride provided good protection of geranium seedlings from zoospore infections but not from mycelial infections. These results suggest that this fungicide must be used preventively for Phytophthora disease management and that mycelial growth may not be the most reliable measurement to determine the development of fungicide resistance to this compound in Phytophthora species at production facilities and in the landscape.

The effect of nursery substrate and fertilization on the growth and ectomycorrhizal status of containerized and outplanted seedlings of Picea abies

2009 ◽  
Vol 39 (1) ◽  
pp. 64-75 ◽  
Author(s):  
Lu-Min Vaario ◽  
Arja Tervonen ◽  
Kati Haukioja ◽  
Markku Haukioja ◽  
Taina Pennanen ◽  
...  
Keyword(s):  
Growth Rate ◽  
Picea Abies ◽  
Norway Spruce ◽  
Growth And Development ◽  
Organic Fertilizer ◽  
Wood Fibre ◽  
Organic Fertilizers ◽  
Relative Growth ◽  
Ecm Fungi ◽  
Influence Of Substrate

Over a 5 year period, we examined the influence of substrate and fertilization on nursery growth and outplanting performance of Norway spruce (Picea abies (L.) Karst.). We focused on the relative growth and development of roots and shoots and the colonization intensity and diversity of ectomycorrhizal (ECM) fungi. In the nursery, a conventional substrate (low-humified Sphagnum peat) supplemented with woody material (wood fibre and pine bark) and either mineral or organic fertilizers yielded shorter seedlings than those grown on the unmodified substrate. However, after outplanting, the growth rate of seedlings cultivated on modified substrates was higher than that of seedlings grown on the unmodified substrate. Seedlings cultivated in modified substrates had significantly higher root/shoot ratios and ECM diversity; the latter remained significant after ≥3 years of outplanting. Seedlings grown on a substrate containing 50% woody material and supplemented with organic fertilizer had the highest growth rate among all seedlings during the 3 year period of outplanting. Colonization intensity of ECM fungi was high in all seedlings except for those grown in heavily fertilized substrate. This study suggests that nursery techniques that produce seedlings with higher root/shoot ratios and ECM diversities could improve plantation success and growth rate for at least the first 3 years of outplanting.

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