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Salmaninezhad F, Mostowfizadeh-Ghalamfarsa R, Cacciola SO. Pythium banihashemianum sp. nov. and Globisporangium izadpanahii sp. nov.: Two New Oomycete Species from Rice Paddies in Iran. J Fungi (Basel) 2024; 10:405. [PMID: 38921391 PMCID: PMC11204656 DOI: 10.3390/jof10060405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2024] [Revised: 05/31/2024] [Accepted: 06/02/2024] [Indexed: 06/27/2024] Open
Abstract
An investigation into oomycete diversity in rice paddies of Fars Province in Iran led to the identification of two new Pythium sensu lato (s.l.) species as Globisporangium izadpanahii sp. nov. and Pythium banihashemianum sp. nov. The identification was based on morphological and physiological features as well as on the phylogenetic analysis of nuclear (ITS and βtub) and mitochondrial (cox1 and cox2) loci using Bayesian inference and Maximum Likelihood. The present paper formally describes these two new species and defines their phylogenetic relationships with other congeneric species. According to multiple gene genealogy analysis, G. izadpanahii sp. nov. was grouped with other species of Globisporangium (formerly, clade G of Pythium s.l.) and was closely related to both G. nagaii and the recently described G. coniferarum. The second species, designated P. banihashemianum sp. nov., was grouped with other species of Pythium sensu stricto (formerly, clade B of Pythium s.l.) and, according to the phylogenetic analysis, shared an ancestor with P. plurisporium. The production of globose hyphal swellings was a major characteristic of G. izadpanahii sp. nov., which did not produce vesicles and zoospores. In pathogenicity tests on rice seedlings, P. banihashemianum sp. nov. isolates were highly pathogenic and caused severe root and crown rot, while G. izadpanahii sp. nov. isolates were not pathogenic.
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Affiliation(s)
- Fatemeh Salmaninezhad
- Department of Plant Protection, School of Agriculture, Shiraz University, Shiraz 7144167186, Iran;
| | | | - Santa Olga Cacciola
- Department of Agriculture, Food and Environment (Di3A), University of Catania, 95123 Catania, Italy
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New Reports of Phytophthora Species in Plant Nurseries in Spain. Pathogens 2022; 11:pathogens11080826. [PMID: 35894049 PMCID: PMC9394253 DOI: 10.3390/pathogens11080826] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 07/20/2022] [Accepted: 07/21/2022] [Indexed: 02/04/2023] Open
Abstract
The plant nursery industry has become an ideal reservoir for Phytophthora species and other soilborne pathogens. In this context, isolation from tissues and soil of ornamental and forest plants from nurseries in four regions of Spain was carried out. A high diversity of Phytophthora species was confirmed. Fourteen Phytophthora phylotypes (P. cactorum, P. cambivora, P. cinnamomi, P. citrophthora, P. crassamura, P. gonapodyides, P. hedraiandra, P. nicotianae, P. niederhauserii, P. palmivora, P. plurivora, P. pseudocryptogea, P. sansomeana, and Phytophthora sp. tropicalis-like 2) were isolated from over 500 plant samples of 22 species in 19 plant genera. Nine species were detected in water sources, two of them (P. bilorbang and P. lacustris) exclusively from water samples. P. crassamura was detected for the first time in Spain. This is the first time P. pseudocryptogea is isolated from Chamaecyparis lawsoniana and Yucca rostrata in Spain.
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Peronosporales Species Associated with Strawberry Crown Rot in the Czech Republic. J Fungi (Basel) 2022; 8:jof8040346. [PMID: 35448577 PMCID: PMC9024537 DOI: 10.3390/jof8040346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 03/23/2022] [Accepted: 03/25/2022] [Indexed: 11/17/2022] Open
Abstract
The symptoms of crown rot on strawberry plants are considered typical for the pathogen Phytophthora cactorum, which causes high losses of this crop. However, an unknown number of related species of pathogens of Peronosporales cause symptoms quite similar to those caused by P. cactorum. To determine their spectrum and importance, strawberry plants were sampled from 41 farms in the Czech Republic. The cultures were isolated from the symptomatic plants using the baiting method, with subsequent cultivation on a semiselective medium. Isolates were identified to the species level using nuclear ribosomal internal transcribed spacer (ITS) barcoding after preliminary morphological determination. In total, 175 isolates of 24 species of Phytophthora, Phytopythium, Pythium, and Globisporangium were detected. The most represented was Phytophthora cactorum, with 113 (65%) isolates, which was recorded in 61% of farms, and the Pythium dissotocum complex with 20 (11%) isolates, which was recorded in 27% of farms. Other species were represented in units of percent. Large differences between farms in the species spectra were ascertained. The differences between species in cardinal growth temperatures and different management of the farms are discussed as a main reason for such a diversification. Regarding the dissimilar sensitivity of various species of Peronosporales against fungicides, the proper determination of the cause of disease is of crucial significance in plant protection.
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Rushford CA, North RL, Miller GL. Detection of Pythium spp. in Golf Course Irrigation Systems. PLANT DISEASE 2022; 106:46-56. [PMID: 34569825 DOI: 10.1094/pdis-02-21-0399-re] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Many Pythium spp. are causal agents of diseases of turfgrasses. Pythium spp. disseminate through irrigation systems in agricultural settings, and this study provides evidence that Pythium spp. also disseminate through golf course irrigation. Water samples were collected from irrigation heads and water sources at 10 golf courses in Missouri and Kansas, U.S.A. Samples were collected from 2018 to 2019 in April, July, and October. Phosphorus, nitrogen, and chloride concentrations were measured from irrigation head samples to determine if these parameters influence frequency of Pythium spp. detected. Pythium spp. were detected in samples through baiting and membrane filtration. Cultures were isolated on PARP media, and DNA was extracted from putative Pythium isolates. The internal transcribed spacer region was PCR-amplified and sequenced. Phylogenetic trees were constructed using representative sample sequences, sequences from seven morphologically identified reference isolates of Pythium, and similar GenBank accessions. Detected oomycete species include Lagenidium giganteum, Pythium biforme, Pythium insidiosum, Pythium marsipium, Pythium plurisporium, and Saprolegnia hypogyna. Twenty-one clades lacked species-level resolution, and 14 of these clades were associated with Pythium species. Clades A, C, D, E, I, and M contain Pythium species that cause root and crown rot on creeping bentgrass. Detected Pythium communities were dependent on the detection method used and sampling source. Pythium frequency and diversity were highest in April 2019. Sample temperature, sampling site, and chloride and nutrient concentrations did not influence Pythium frequency in samples. Irrigation systems using surface water sources contained at least three Pythium spp. over the course of 2 years.
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Affiliation(s)
| | - Rebecca L North
- School of Natural Resources, University of Missouri, Columbia, MO 65211
| | - Gerald L Miller
- Division of Plant Science, University of Missouri, Columbia, MO 65211
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The Threat of Pests and Pathogens and the Potential for Biological Control in Forest Ecosystems. FORESTS 2021. [DOI: 10.3390/f12111579] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Forests are an essential component of the natural environment, as they support biodiversity, sequester carbon, and play a crucial role in biogeochemical cycles—in addition to producing organic matter that is necessary for the function of terrestrial organisms. Forests today are subject to threats ranging from natural occurrences, such as lightning-ignited fires, storms, and some forms of pollution, to those caused by human beings, such as land-use conversion (deforestation or intensive agriculture). In recent years, threats from pests and pathogens, particularly non-native species, have intensified in forests. The damage, decline, and mortality caused by insects, fungi, pathogens, and combinations of pests can lead to sizable ecological, economic, and social losses. To combat forest pests and pathogens, biocontrol may be an effective alternative to chemical pesticides and fertilizers. This review of forest pests and potential adversaries in the natural world highlights microbial inoculants, as well as research efforts to further develop biological control agents against forest pests and pathogens. Recent studies have shown promising results for the application of microbial inoculants as preventive measures. Other studies suggest that these species have potential as fertilizers.
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Davis EA, Weiland JE, Scagel CF. Optimizing Inoculum Production Methods for Infesting Soil with Phytophthora Species. PLANT DISEASE 2021; 105:2970-2974. [PMID: 33779252 DOI: 10.1094/pdis-12-20-2698-re] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Inoculum production is an important part of conducting research with soilborne Phytophthora species. One common method is to incubate Phytophthora cultures in nutrient-amended vermiculite. However, inoculum levels often vary among batches of inoculum, even when production methods remain the same, and incubation typically takes ≥6 weeks, increasing risks for delayed experiments if the resulting inoculum level is too low. A more reliable and rapid method is needed for future studies. Experiments were conducted to determine inoculum levels of Phytophthora cinnamomi and Phytophthora plurivora after incubation in V8 juice-amended vermiculite (standard method); evaluate how inoculum viability was affected by air-drying; develop a modified method that takes less time to produce a vermiculite-based inoculum; and evaluate the effect of storage on inoculum viability. Results showed that the standard method produced inoculum levels from 716 to 1,808 colony forming units (CFUs)/g and that drying to <78% moisture content significantly reduced viability. The modified method used 2-week-old Phytophthora cultures to infest vermiculite at 80% moisture content and produced inoculum levels from 214 to 525 CFU/g. Storage for >1 day generally reduced inoculum viability. Although inoculum levels from the modified method were lower than the standard method, inoculum levels for each isolate were more consistent between trials, and the modified method was 6 to 8 weeks faster. Production with the modified method can also be easily scaled up by infesting a greater volume of vermiculite with additional cultures of Phytophthora. These results are important because they help explain variability in soilborne Phytophthora inoculum production and storage and provide a new method for producing inoculum more quickly.
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Affiliation(s)
- E Anne Davis
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture, Agricultural Research Service, Corvallis, OR 97330
| | - Jerry E Weiland
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture, Agricultural Research Service, Corvallis, OR 97330
| | - Carolyn F Scagel
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture, Agricultural Research Service, Corvallis, OR 97330
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Phytopythium vexans Associated with Apple and Pear Decline in the Saïss Plain of Morocco. Microorganisms 2021; 9:microorganisms9091916. [PMID: 34576811 PMCID: PMC8468409 DOI: 10.3390/microorganisms9091916] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2021] [Revised: 09/05/2021] [Accepted: 09/07/2021] [Indexed: 11/17/2022] Open
Abstract
An extensive survey conducted in the Saïss plain of Morocco during the 2017-2018 growing season revealed that 35 out of 50 apple and pear orchards were infested with a pathogen that causes the decline disease. Morphological and phylogenetic tree analyses using the cox II gene allowed us to identify the pathogen as Phytopythium vexans. Interestingly, no Phytophthora and Pythium species were isolated. The occurrence and prevalence of the disease varied between locations; the most infested locations were Meknes (100%), Imouzzer (83%), and Sefrou (80%). To fulfill Koch's postulate, a greenhouse pathogenicity test was performed on the stem and collar of one-year-old healthy seedlings of apple rootstock M115. Symptoms similar to those observed in the field were reproduced in less than 4 months post-inoculation with root rot disease severity ranging from 70 to 100%. The survey results evidenced that apple rootstocks, soil type, and irrigation procedure may contribute significantly to the occurrence of the disease. The disease was most prevalent in drip water irrigation and sandy-clay soil on wild apple rootstock. Accordingly, a rational drip advanced watering system and good sanitation practices could eliminate water stagnation and help prevent the onset of this disease. It was concluded that Pp. vexans occurrence may be strongly influenced by irrigation mode and type of soil. Therefore, the obtained findings of this study could help to better understand the recurrence of this disease and to develop a reliable integrated strategy for its management.
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Puertolas A, Bonants PJM, Boa E, Woodward S. Application of Real-Time PCR for the Detection and Quantification of Oomycetes in Ornamental Nursery Stock. J Fungi (Basel) 2021; 7:jof7020087. [PMID: 33513806 PMCID: PMC7911672 DOI: 10.3390/jof7020087] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/21/2021] [Accepted: 01/24/2021] [Indexed: 11/16/2022] Open
Abstract
Numerous Phytophthora and Pythium disease outbreaks have occurred in Europe following inadvertent introduction of contaminated ornamental plants. Detection and identification of pathogens are crucial to reduce risks and improve plant biosecurity in Europe and globally. Oomycete diversity present in roots and compost was determined in 99 hardy woody plants bought from nurseries, retailers and internet sellers, using both isolations and molecular analyses. Oomycete DNA was quantified using real-time PCR of environmental DNA from the plants using three loci: ITS, trnM-trnP-trnM and atp9-nad9. At least one oomycete species was isolated from 89.9% of plants using classical techniques. In total, 10 Phytophthora spp., 17 Pythium spp. and 5 Phytopythium spp. were isolated. Oomycetes were isolated from 86% of asymptomatic plants, but real-time PCR demonstrated that oomycetes were associated with all plants tested. More oomycete DNA occurred in composts in comparison with roots and filters from baiting water (a mean of 7.91 ng g−1, 6.55 × 10−1 ng g−1 and 5.62 × 10−1 ng g−1 of oomycete DNA detected in compost with ITS, trnM and atp9 probes, respectively); the ITS probe detected the highest quantities of oomycete DNA. No significant differences were found in quantities of oomycete DNA detected using real-time PCR in plants purchased online or from traditional retailers.
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Affiliation(s)
- Alexandra Puertolas
- ANSES, Laboratoire de la Santé des Végétaux-Unité de Mycologie, Domaine de Pixérécourt-Bât. E, CS 40009, F54220 Malzéville, France;
- Department of Plant and Soil Science, School of Biological Sciences, University of Aberdeen, Aberdeen, Scotland AB24 3UU, UK;
| | - Peter J. M. Bonants
- Wageningen Plant Research, Business Unit Biointeractions & Plant Health, Wageningen UR, 6700 AA Wageningen, The Netherlands;
| | - Eric Boa
- Department of Plant and Soil Science, School of Biological Sciences, University of Aberdeen, Aberdeen, Scotland AB24 3UU, UK;
| | - Steve Woodward
- Department of Plant and Soil Science, School of Biological Sciences, University of Aberdeen, Aberdeen, Scotland AB24 3UU, UK;
- Correspondence: ; Tel.: +44-1224-272-669
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Jayawardena RS, Hyde KD, Chen YJ, Papp V, Palla B, Papp D, Bhunjun CS, Hurdeal VG, Senwanna C, Manawasinghe IS, Harischandra DL, Gautam AK, Avasthi S, Chuankid B, Goonasekara ID, Hongsanan S, Zeng X, Liyanage KK, Liu N, Karunarathna A, Hapuarachchi KK, Luangharn T, Raspé O, Brahmanage R, Doilom M, Lee HB, Mei L, Jeewon R, Huanraluek N, Chaiwan N, Stadler M, Wang Y. One stop shop IV: taxonomic update with molecular phylogeny for important phytopathogenic genera: 76–100 (2020). FUNGAL DIVERS 2020. [DOI: 10.1007/s13225-020-00460-8] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
AbstractThis is a continuation of a series focused on providing a stable platform for the taxonomy of phytopathogenic fungi and fungus-like organisms. This paper focuses on one family: Erysiphaceae and 24 phytopathogenic genera: Armillaria, Barriopsis, Cercospora, Cladosporium, Clinoconidium, Colletotrichum, Cylindrocladiella, Dothidotthia,, Fomitopsis, Ganoderma, Golovinomyces, Heterobasidium, Meliola, Mucor, Neoerysiphe, Nothophoma, Phellinus, Phytophthora, Pseudoseptoria, Pythium, Rhizopus, Stemphylium, Thyrostroma and Wojnowiciella. Each genus is provided with a taxonomic background, distribution, hosts, disease symptoms, and updated backbone trees. Species confirmed with pathogenicity studies are denoted when data are available. Six of the genera are updated from previous entries as many new species have been described.
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Riga E, Crisp JD, McComb GJ, Weiland JE, Zasada IA. Directed energy system technology for the control of soilborne fungal pathogens and plant-parasitic nematodes. PEST MANAGEMENT SCIENCE 2020; 76:2072-2078. [PMID: 31943776 DOI: 10.1002/ps.5745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 01/02/2020] [Accepted: 01/13/2020] [Indexed: 06/10/2023]
Abstract
BACKGROUND It is challenging to manage soilborne pathogens and plant-parasitic nematodes using sustainable practices. Here, we evaluated a novel energy application system, Directed Energy System (DES). This system generates pulses of energy capable of impacting selected biological organisms. The oomycete Phytophthora cinnamomi, the fungus Verticillium dahliae, and the plant-parasitic nematodes Meloidogyne hapla and Globodera ellingtonae were added to soil. Then DES-generated energy was applied to soil and impacts on target organisms were determined. RESULTS DES applied at 20, 40 and 70 J cm-3 to P. cinnamomi and V. dahliae resulted in ≥50% and 92% reductions (respectively) of propagules per gram of soil in comparison to the untreated control. There was a significant reduction of M. hapla eggs per gram of host tomato root between the untreated control, and 2.2, 13 and 25 J cm-3 DES dosages applied pre- or post-planting. Additionally, an 84% reduction in hatch from G. ellingtonae encysted eggs after treatment with 70 J cm-3 DES was observed. The dosages ranged from 40 or 80V mm-1 for nematodes to 200 V mm-1 for fungi. CONCLUSION DES-generated energy reduced survival of the soilborne pathogens P. cinnamomi and V. dahlia, and the plant-parasitic nematodes M. hapla and G. ellingtonae. The application of this technology to a field setting remains to be considered. Published 2020. This article is a U.S. Government work and is in the public domain in the USA. Pest Management Science published by Wiley Periodicals, Inc. on behalf of © 2020 Society of Chemical Industry.
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Affiliation(s)
| | | | | | - Jerry E Weiland
- USDA-Agricultural Research Service Horticultural Crops Research Unit, Corvallis, OR, USA
| | - Inga A Zasada
- USDA-Agricultural Research Service Horticultural Crops Research Unit, Corvallis, OR, USA
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Weiland JE, Scagel CF, Grünwald NJ, Davis EA, Beck BR, Foster ZSL, Fieland VJ. Soilborne Phytophthora and Pythium Diversity From Rhododendron in Propagation, Container, and Field Production Systems of the Pacific Northwest. PLANT DISEASE 2020; 104:1841-1850. [PMID: 32370604 DOI: 10.1094/pdis-08-19-1672-re] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Rhododendron root rot is a severe disease that causes significant mortality in rhododendrons. Information is needed about the incidence and identity of soilborne Phytophthora and Pythium species causing root rot in Pacific Northwest nurseries in order to better understand the disease etiology and to optimize disease control strategies. The last survey focusing solely on soilborne oomycete pathogens in rhododendron production was conducted in 1974. Since then, advances in pathogen identification have occurred, new species may have been introduced, pathogen communities may have shifted, and little is known about Pythium species affecting this crop. Therefore, a survey of root-infecting Phytophthora and Pythium species was conducted at seven nurseries from 2013 to 2017 to (i) document the incidence of root rot damage at each nursery and stage of production, (ii) identify soilborne oomycetes infecting rhododendron, and (iii) determine whether there are differences in pathogen diversity among nurseries and production systems. Rhododendrons from propagation, container, and field systems were sampled and Phytophthora and Pythium species were isolated from the roots and collar region. Root rot was rarely evident in propagation systems, which were dominated by Pythium species. However, severe root rot was much more common in container and field systems where the genus Phytophthora was also more prevalent, suggesting that Phytophthora species are the primary cause of severe root rot and that most contamination by these pathogens comes in after the propagation stage. In total, 20 Pythium species and 11 Phytophthora species were identified. Pythium cryptoirregulare, Pythium aff. macrosporum, Phytophthora plurivora, and Phytophthora cinnamomi were the most frequently isolated species and the results showed that Phytophthora plurivora has become much more common than in the past. Phytophthora diversity was also greater in field systems than in propagation or container systems. Risks for Phytophthora contamination were commonly observed during the survey and included placement of potting media in direct contact with field soil, the presence of dead plants that could serve as continuous sources of inoculum, and the presence of excess water as a result of poor drainage, overirrigation, or malfunctioning irrigation equipment. In the past, research on disease development and root rot disease control in rhododendron focused almost exclusively on Phytophthora cinnamomi. More research is needed on both of these topics for the other root-infecting species identified in this survey.
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Affiliation(s)
- Jerry E Weiland
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture Agricultural Research Service, Corvallis, OR 97330
| | - Carolyn F Scagel
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture Agricultural Research Service, Corvallis, OR 97330
| | - Niklaus J Grünwald
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture Agricultural Research Service, Corvallis, OR 97330
| | - E Anne Davis
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture Agricultural Research Service, Corvallis, OR 97330
| | - Bryan R Beck
- Horticultural Crops Research Laboratory, U.S. Department of Agriculture Agricultural Research Service, Corvallis, OR 97330
| | - Zachary S L Foster
- Oregon State University, Department of Botany and Plant Pathology, Corvallis, OR 97331
| | - Valerie J Fieland
- Oregon State University, Department of Botany and Plant Pathology, Corvallis, OR 97331
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Del Castillo Múnera J, Quesada-Ocampo LM, Rojas A, Chilvers MI, Hausbeck MK. Population Structure of Pythium ultimum from Greenhouse Floral Crops in Michigan. PLANT DISEASE 2019; 103:859-867. [PMID: 30908944 DOI: 10.1094/pdis-03-18-0394-re] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Pythium ultimum causes seedling damping-off and root and crown rot in greenhouse ornamental plants. To understand the population dynamics and assess population structure of P. ultimum in Michigan floriculture crops, simple sequence repeats (SSRs) were developed using the previously published P. ultimum predicted transcriptome. A total of 166 isolates sampled from 2011 to 2013 from five, one, and three greenhouses in Kalamazoo, Kent, and Wayne Counties, respectively, were analyzed using six polymorphic and fluorescently labeled SSR markers. The average unbiased Simpson's index (λu, 0.95), evenness (E5, 0.56), and recovery of 12 major clones out of the 65 multilocus genotypes obtained, suggests that P. ultimum is not a recent introduction into Michigan greenhouses. Analyses revealed a clonal population, with limited differentiation among seasons, hosts, and counties sampled. Results also indicated the presence of common genotypes among years, suggesting that sanitation measures should be enhanced to eradicate resident P. ultimum populations. Finally, the presence of common genotypes among counties suggests that there is an exchange of infected plant material among greenhouse facilities, or that there is a common source of inoculum coming to the region. Continued monitoring of pathogen populations will enhance our understanding of population dynamics of P. ultimum in Michigan and facilitate improvement of control strategies.
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Affiliation(s)
| | | | - Alejandro Rojas
- 3 Department of Plant Pathology, University of Arkansas, Fayetteville, AR 72701
| | - Martin I Chilvers
- 4 Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, 48824
| | - Mary K Hausbeck
- 4 Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, 48824
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Abstract
In an investigation of the oomyceteous flora in rice paddy fields of Fars Province, Iran, three new Pythium species were isolated and identified on the basis of morphological features and molecular phylogenetic characteristics. Their unique morphological traits, including sexual and asexual structural characteristics (i.e., sporangial type; oogonial type and ornamentations; type and the number of antheridia per oogonium; and oospore type), cardinal temperatures, and colony morphology on various media, separated them from other known species. Using nuclear and mitochondrial genes, each species formed discrete lineages in phylogenetic analyses based on Bayesian inference and maximum likelihood methods. This paper describes these three new Pythium species, P. heteroogonium, P. longipapillum, and P. oryzicollum, and compares them with their related taxa via morphological features and molecular characteristics. Pathogenicity tests revealed the ability of P. oryzicollum to cause pre- and post-emergence damping-off, seed rot, crown rot, and reduced growth rate on rice.
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Affiliation(s)
- Fatemeh Salmaninezhad
- a Department of Plant Protection , School of Agriculture, Shiraz University , Shiraz , Iran 7144167186
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Mercado-Blanco J, Abrantes I, Barra Caracciolo A, Bevivino A, Ciancio A, Grenni P, Hrynkiewicz K, Kredics L, Proença DN. Belowground Microbiota and the Health of Tree Crops. Front Microbiol 2018; 9:1006. [PMID: 29922245 PMCID: PMC5996133 DOI: 10.3389/fmicb.2018.01006] [Citation(s) in RCA: 80] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 04/30/2018] [Indexed: 11/13/2022] Open
Abstract
Trees are crucial for sustaining life on our planet. Forests and land devoted to tree crops do not only supply essential edible products to humans and animals, but also additional goods such as paper or wood. They also prevent soil erosion, support microbial, animal, and plant biodiversity, play key roles in nutrient and water cycling processes, and mitigate the effects of climate change acting as carbon dioxide sinks. Hence, the health of forests and tree cropping systems is of particular significance. In particular, soil/rhizosphere/root-associated microbial communities (known as microbiota) are decisive to sustain the fitness, development, and productivity of trees. These benefits rely on processes aiming to enhance nutrient assimilation efficiency (plant growth promotion) and/or to protect against a number of (a)biotic constraints. Moreover, specific members of the microbial communities associated with perennial tree crops interact with soil invertebrate food webs, underpinning many density regulation mechanisms. This review discusses belowground microbiota interactions influencing the growth of tree crops. The study of tree-(micro)organism interactions taking place at the belowground level is crucial to understand how they contribute to processes like carbon sequestration, regulation of ecosystem functioning, and nutrient cycling. A comprehensive understanding of the relationship between roots and their associate microbiota can also facilitate the design of novel sustainable approaches for the benefit of these relevant agro-ecosystems. Here, we summarize the methodological approaches to unravel the composition and function of belowground microbiota, the factors influencing their interaction with tree crops, their benefits and harms, with a focus on representative examples of Biological Control Agents (BCA) used against relevant biotic constraints of tree crops. Finally, we add some concluding remarks and suggest future perspectives concerning the microbiota-assisted management strategies to sustain tree crops.
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Affiliation(s)
- Jesús Mercado-Blanco
- Department of Crop Protection, Agencia Estatal Consejo Superior de Investigaciones Científicas, Institute for Sustainable Agriculture, Córdoba, Spain
| | - Isabel Abrantes
- Department of Life Sciences, Centre for Functional Ecology, University of Coimbra, Coimbra, Portugal
| | | | - Annamaria Bevivino
- Department for Sustainability of Production and Territorial Systems, Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Rome, Italy
| | - Aurelio Ciancio
- Institute for Sustainable Plant Protection, National Research Council, Bari, Italy
| | - Paola Grenni
- Water Research Institute (CNR-IRSA), National Research Council, Rome, Italy
| | - Katarzyna Hrynkiewicz
- Department of Microbiology, Faculty of Biology and Environmental Protection, Nicolaus Copernicus University, Toruń, Poland
| | - László Kredics
- Department of Microbiology, Faculty of Science and Informatics, University of Szeged, Szeged, Hungary
| | - Diogo N. Proença
- Centre for Mechanical Engineering, Materials and Processes (CEMMPRE) and Department of Life Sciences, University of Coimbra, Coimbra, Portugal
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15
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Coffua LS, Veterano ST, Clipman SJ, Mena-Ali JI, Blair JE. Characterization of Pythium spp. Associated with Asymptomatic Soybean in Southeastern Pennsylvania. PLANT DISEASE 2016; 100:1870-1879. [PMID: 30682988 DOI: 10.1094/pdis-11-15-1355-re] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Soybean production in Pennsylvania has increased substantially over the past 20 years and is a highly valued field crop, together with corn. Soilborne pathogens such as Pythium spp. can contribute to soybean stand establishment issues, particularly under the conservation tillage practices that are common in the state. In this study, we collected soil samples from eight asymptomatic soybean-corn rotation fields across six counties in southeastern Pennsylvania between May and June 2012. Pythium spp. were isolated via baiting, and tested for aggressiveness on both soybean and corn using laboratory assays. In addition to our culture-based survey, we also assessed the use of cytochrome oxidase subunit 1 pyrosequencing as a culture-independent method for measuring Pythium spp. diversity from environmental samples. Diversity estimates were consistent between the culture-based and pyrosequencing datasets; however, important methodological biases inherent to culture-independent methods may have led to some differences. Our results show that several Pythium spp. previously characterized as soybean or corn pathogens are present in southeastern Pennsylvania, including Pythium irregulare, P. sylvaticum, and P. ultimum var. sporangiiferum, with isolates showing aggressive phenotypes in lab assays.
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Affiliation(s)
- Lauren S Coffua
- Department of Biology, Franklin & Marshall College, Lancaster, PA 17603
| | - S Tyler Veterano
- Department of Biology, Franklin & Marshall College, Lancaster, PA 17603
| | - Steven J Clipman
- Department of Biology, Franklin & Marshall College, Lancaster, PA 17603
| | - Jorge I Mena-Ali
- Department of Biology, Franklin & Marshall College, Lancaster, PA 17603
| | - Jaime E Blair
- Department of Biology, Franklin & Marshall College, Lancaster, PA 17603
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16
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Choudhary CE, Burgos-Garay ML, Moorman GW, Hong C. Pythium and Phytopythium Species in Two Pennsylvania Greenhouse Irrigation Water Tanks. PLANT DISEASE 2016; 100:926-932. [PMID: 30686146 DOI: 10.1094/pdis-07-15-0836-re] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Two commercial greenhouses producing potted plants in Pennsylvania using recycled irrigation water in an ebb-and-flood system have incurred significant crop losses due to Pythium aphanidermatum. In cooperation with the greenhouses, one or more of their water tanks was monitored continuously (128 tank samplings) for Pythium spp. by baiting. Nine species of Pythium and three species of Phytopythium were recovered, representing clades A, B, E, and K, but none was P. aphanidermatum. The recovered Pythium spp. were (i) P. rostratifingens, (ii) isolates identical to Pythium sp. nov. OOMYA1702-08 (clade B2), (iii) P. coloratum, (iv) P. middletonii, (v) and (vi) two new species in clade E2, (vii) a new species in clade B2, (viii) isolates very similar to Pythium sp. nov. OOMYA1646-08 (clade E2), and (ix) a new species in clade A. The Phytopythium spp. recovered were (i) Phytopythium litorale, (ii) P. helicoides, and (iii) P. chamaehyphon. This article illustrates the different communities of Pythium and Phytopythium spp. found in each greenhouse over 10 months. Some of the baited species display resistance to the oomycete fungicide active ingredient, mefenoxam. P. helicoides and the new species in clade B2 were pathogenic on seedlings in potting mix with fertilizer added.
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Affiliation(s)
- Carla E Choudhary
- Department of Plant Pathology & Environmental Microbiology, The Pennsylvania State University, University Park 16802
| | - Maria L Burgos-Garay
- Department of Plant Pathology & Environmental Microbiology, The Pennsylvania State University, University Park 16802
| | - Gary W Moorman
- Department of Plant Pathology & Environmental Microbiology, The Pennsylvania State University, University Park 16802
| | - Chuanxue Hong
- Virginia Polytechnic Institute and State University, Hampton Roads Agricultural Research and Extension Center, Virginia Beach 23455
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17
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Del Castillo Múnera J, Hausbeck MK. Characterization of Pythium Species Associated With Greenhouse Floriculture Crops in Michigan. PLANT DISEASE 2016; 100:569-576. [PMID: 30688597 DOI: 10.1094/pdis-03-15-0296-re] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Michigan ranks third in the United States for the wholesale value of floriculture products, with an estimated value of $375.7 million. Seedling damping-off and root and crown rot are commonly caused by Pythium spp. and are important problems for greenhouse growers. Pythium spp. associated with Michigan's floriculture crops were characterized as a means to improve current management strategies. During 2011 and 2012, potted poinsettias with root rot symptoms were sampled from nine greenhouses located in Kent, Kalamazoo, and Wayne counties. In 2013, from the same three counties, symptomatic geranium and snapdragon bedding plants were sampled from 12 greenhouses. Additionally, symptomatic hibiscus and lantana plants were sampled at one greenhouse facility. Isolates were confirmed to be Pythium spp. via morphology and sequencing of the ITS region. A total of 287 Pythium spp. isolates were obtained from poinsettias and 726 isolates from geranium, snapdragon, hibiscus, and lantana. Seven Pythium spp., and a group of isolates determined as Pythium sp. 1 were identified. The most prevalent species were P. irregulare, P. ultimum, and P. aphanidermatum. A subset of isolates was chosen for pathogenicity and mefenoxam sensitivity testing. Six of the species were virulent to germinating geranium seeds. Most P. ultimum and P. cylindrosporum isolates tested were intermediate to highly resistant to mefenoxam, whereas most P. aphanidermatum isolates were sensitive. This study suggests that Pythium spp. recovered from Michigan greenhouses may vary depending on the host, and that mefenoxam may not be effective to control P. ultimum or P. cylindrosporum.
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Affiliation(s)
| | - Mary K Hausbeck
- Professor, Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing 48824
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18
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Weiland JE, Garrido P, Kamvar ZN, Espíndola AS, Marek SM, Grünwald NJ, Garzón CD. Population Structure of Pythium irregulare, P. ultimum, and P. sylvaticum in Forest Nursery Soils of Oregon and Washington. PHYTOPATHOLOGY 2015; 105:684-694. [PMID: 25607720 DOI: 10.1094/phyto-05-14-0147-r] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Pythium species are important soilborne pathogens occurring in the forest nursery industry of the Pacific Northwest. However, little is known about their genetic diversity or population structure and it is suspected that isolates are moved among forest nurseries on seedling stock and shared field equipment. In order to address these concerns, a total of 115 isolates of three Pythium species (P. irregulare, P. sylvaticum, and P. ultimum) were examined at three forest nurseries using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. Analyses revealed distinct patterns of intraspecific variation for the three species. P. sylvaticum exhibited the most diversity, followed by P. irregulare, while substantial clonality was found in P. ultimum. For both P. irregulare and P. sylvaticum, but not P. ultimum, there was evidence for significant variation among nurseries. However, all three species also exhibited at least two distinct lineages not associated with the nursery of origin. Finally, evidence was found that certain lineages and clonal genotypes, including fungicide-resistant isolates, are shared among nurseries, indicating that pathogen movement has occurred.
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Affiliation(s)
- Jerry E Weiland
- First and sixth authors: U.S. Department of Agriculture-Agriculture Research Service, Horticultural Crops Research Laboratory, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331; second, fourth, fifth, and seventh authors: Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74074; and third author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
| | - Patricia Garrido
- First and sixth authors: U.S. Department of Agriculture-Agriculture Research Service, Horticultural Crops Research Laboratory, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331; second, fourth, fifth, and seventh authors: Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74074; and third author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
| | - Zhian N Kamvar
- First and sixth authors: U.S. Department of Agriculture-Agriculture Research Service, Horticultural Crops Research Laboratory, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331; second, fourth, fifth, and seventh authors: Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74074; and third author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
| | - Andrés S Espíndola
- First and sixth authors: U.S. Department of Agriculture-Agriculture Research Service, Horticultural Crops Research Laboratory, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331; second, fourth, fifth, and seventh authors: Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74074; and third author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
| | - Stephen M Marek
- First and sixth authors: U.S. Department of Agriculture-Agriculture Research Service, Horticultural Crops Research Laboratory, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331; second, fourth, fifth, and seventh authors: Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74074; and third author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
| | - Niklaus J Grünwald
- First and sixth authors: U.S. Department of Agriculture-Agriculture Research Service, Horticultural Crops Research Laboratory, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331; second, fourth, fifth, and seventh authors: Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74074; and third author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
| | - Carla D Garzón
- First and sixth authors: U.S. Department of Agriculture-Agriculture Research Service, Horticultural Crops Research Laboratory, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331; second, fourth, fifth, and seventh authors: Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74074; and third author: Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
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19
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Erşahin YŞ, Weiland JE, Zasada IA, Reed RL, Stevens JF. Identifying Rates of Meadowfoam (Limnanthes alba) Seed Meal Needed for Suppression of Meloidogyne hapla and Pythium irregulare in Soil. PLANT DISEASE 2014; 98:1253-1260. [PMID: 30699611 DOI: 10.1094/pdis-09-13-0967-re] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Meadowfoam (Limnanthes alba) is a commercial oilseed annual crop grown in Oregon. After extracting oil from seed, the remaining seed meal is rich in the secondary plant metabolite glucolimnanthin, which can be converted into pesticidal compounds such as 3-methoxybenzyl isothiocyanate (ITC) and 3-methoxyphenylacetonitrile (nitrile) in the presence of the enzyme myrosinase. In previous studies, we demonstrated that ITC and nitrile, produced by mixing freshly ground meadowfoam seed with meadowfoam seed meal, are toxic to the plant-parasitic nematode Meloidogyne hapla and the plant pathogen Pythium irregulare. In this study, we evaluated factors that might influence the implementation of meadowfoam seed meal into agricultural production systems for soilborne pathogen and nematode control. Rate-finding experiments demonstrated that a minimum 1.0% seed/seed meal formulation (wt/wt) was necessary to achieve nematode and pathogen suppression; seed meal alone was insufficient for complete control of M. hapla and stimulated the growth of P. irregulare. When this 1.0% seed/seed meal formulation was used, a greater soil amendment rate was required to cause 100% mortality of P. irregulare (1.0% wt/wt) than for M. hapla (0.5% wt/wt). In phytotoxicity experiments, soil amended with the 1.0% seed/seed meal formulation was consistently phytotoxic to wheat, cucumber, and tomato. However, phytotoxic effects were mitigated by a delayed planting into the amended soil. A final assay to monitor concentrations of ITC and nitrile in conjunction with assessing M. hapla and P. irregulare mortality was conducted over a 6-day period in soils amended at 0.5 and 1.0% (wt/wt) with the 1.0% seed/seed meal formulation. The response was rapid, with 100% mortality of both organisms within 2 h after exposure to amended soil. Concentrations of nitrile remained relatively constant over the 6-day period (approximately 0.017 and 0.032 mg/ml at 0.5 and 1.0% amendment rates, respectively), whereas ITC production increased rapidly and peaked 12 to 24 h after amendment (0.083 and 0.171 mg/ml at 0.5 and 1.0% amendment rates, respectively) before returning to near undetectable levels.
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Affiliation(s)
| | - Jerry E Weiland
- United States Department of Agriculture-Agricultural Research Services, Horticultural Crops Research Laboratory, Corvallis, OR 97330
| | - Inga A Zasada
- United States Department of Agriculture-Agricultural Research Services, Horticultural Crops Research Laboratory, Corvallis, OR 97330
| | - Ralph L Reed
- Department of Pharmaceutical Sciences, Oregon State University, Corvallis 97331
| | - J Fred Stevens
- Department of Pharmaceutical Sciences, Oregon State University, Corvallis 97331
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20
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Weiland JE, Santamaria L, Grünwald NJ. Sensitivity of Pythium irregulare, P. sylvaticum, and P. ultimum from Forest Nurseries to Mefenoxam and Fosetyl-Al, and Control of Pythium Damping-off. PLANT DISEASE 2014; 98:937-942. [PMID: 30708838 DOI: 10.1094/pdis-09-13-0998-re] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Mefenoxam and fosetyl-Al are common fungicides used to supplement disease control of Pythium damping-off and root rot in forest nurseries of the western United States. However, it is unknown whether fungicide-resistant Pythium isolates are present or whether new fungicide and biological treatments might also provide supplemental disease control. Isolates of Pythium irregulare, P. sylvaticum, and P. ultimum from three forest nurseries were evaluated for in vitro sensitivity to mefenoxam and fosetyl-Al. A greenhouse study was also conducted to assess efficacy of fungicide and biological treatments in Douglas-fir (Pseudotsuga menziesii) seedlings inoculated with Pythium dissotocum, P. irregulare, and P. 'vipa'. P. irregulare was approximately three times less sensitive to mefenoxam (0.20 μg/ml) than P. sylvaticum (0.06 μg/ml) and P. ultimum (0.06 μg/ml), and two resistant isolates of P. ultimum were identified (≥311 μg/ml). All three Pythium spp. were similarly sensitive to fosetyl-Al (1,256 to 1,508 μg/ml) and no resistant isolates were found. In the disease control efficacy trial, both fosetyl-Al and phosphorous acid consistently provided good protection against damping-off caused by P. dissotocum, P. irregulare, and P. 'vipa'. Other treatments, including mefenoxam, also provided good or intermediate protection but efficacy depended upon which Pythium sp. was used. Growers should consider rotating mefenoxam use with other fungicide chemistries or biological treatments to prevent further development and spread of mefenoxam-resistant isolates.
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Affiliation(s)
- Jerry E Weiland
- United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Horticulture Crops Research Laboratory and Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331
| | - Luisa Santamaria
- Department of Botany and Plant Pathology, Oregon State University
| | - Niklaus J Grünwald
- USDA-ARS Horticulture Crops Research Laboratory and Department of Botany and Plant Pathology, Oregon State University
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21
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Weiland JE. Pythium Species and Isolate Diversity Influence Inhibition by the Biological Control Agent Streptomyces lydicus. PLANT DISEASE 2014; 98:653-659. [PMID: 30708563 DOI: 10.1094/pdis-05-13-0482-re] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Disease control of soilborne pathogens by biological control agents (BCAs) is often inconsistent under field conditions. This inconsistency may be partly influenced by pathogen diversity if there is a differential response among pathogen species and isolates to selected BCAs. The responses of 148 Pythium isolates obtained from soil at three forest nurseries and representative of 16 Pythium spp. were evaluated in the presence of Streptomyces lydicus strain WYEC108 in an in vitro assay. Percent growth inhibition, inhibition zone distance, mortality, and growth rate were recorded for each isolate, and data were analyzed for effects of species and isolate. Responses of three Pythium spp. (Pythium irregulare, P. sylvaticum, and P. ultimum) were further analyzed for a location (nursery) effect. Although S. lydicus inhibited all Pythium isolates, differences in percent growth inhibition, inhibition zone distance, and mortality were observed among Pythium spp. and isolates. Small but significant location effects were also noted. Growth rate also varied among Pythium spp. and isolates and was found to strongly bias percent growth inhibition and, to a lesser degree, inhibition zone distance; depending on which measure was used, slower-growing isolates appeared less sensitive (growth inhibition) or more sensitive (inhibition zone) to S. lydicus than faster-growing isolates. Results illustrate the importance of using multiple, representative pathogen isolates in preliminary BCA inhibition assays as well as accounting for the effect of pathogen growth rate on pathogen inhibition by BCAs. Future studies should take pathogen diversity into account when evaluating biological control efficacy.
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Affiliation(s)
- Jerry E Weiland
- United States Department of Agriculture-Agriculture Research Service, Horticultural Crops Research Laboratory, and Oregon State University, Department of Botany and Plant Pathology, Corvallis 97331
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