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Li YM, Shaffer JP, Hall B, Ko H. Soil-borne fungi influence seed germination and mortality, with implications for coexistence of desert winter annual plants. PLoS One 2019; 14:e0224417. [PMID: 31671129 PMCID: PMC6822719 DOI: 10.1371/journal.pone.0224417] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Accepted: 10/14/2019] [Indexed: 11/25/2022] Open
Abstract
Soil-borne fungi influence coexistence of plant species in mesic environments, but much less is known about their effects on demographic processes relevant to coexistence in arid and semi-arid systems. We isolated 43 fungal strains that naturally colonize seeds of an invasive winter annual (Brassica tournefortii) in the Sonoran Desert, and evaluated the impact of 18 of them on seed germination and mortality of B. tournefortii and a co-occurring native annual (Plantago ovata) under simulated summer and winter temperatures. Fungi isolated from B. tournefortii seeds impacted germination and mortality of seeds of both plant species in vitro. Seed responses reflected host-specific effects by fungi, the degree of which differed significantly between the strains, and depended on the temperature. In the winter temperature, ten fungal strains increased or reduced seed germination, but substantial seed mortality due to fungi was not observed. Two strains increased germination of P. ovata more strongly than B. tournefortii. In the summer temperature, fungi induced both substantial seed germination and mortality, with ten strains demonstrating host-specificity. Under natural conditions, host-specific effects of fungi on seed germination may further differentiate plant species niche in germination response, with a potential of promoting coexistence. Both host-specific and non-host-specific effects of fungi on seed loss may induce polarizing effects on plant coexistence depending on the ecological context. The coexistence theory provides a clear framework to interpret these polarizing effects. Moreover, fungi pathogenic to both plant species could induce host-specific germination, which challenges the theoretical assumption of density-independent germination response. These implications from an in vitro study underscore the need to weave theoretical modeling, reductive empirical experiments, and natural observations to illuminate effects of soil-borne fungi on coexistence of annual plant species in variable desert environments.
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Affiliation(s)
- Yue M. Li
- School of Natural Resources and the Environment, University of Arizona, Tucson, Arizona, United States of America
- Arizona-Sonora Desert Museum, Tucson, Arizona, United States of America
| | - Justin P. Shaffer
- School of Plant Sciences, University of Arizona, Tucson, Arizona, United States of America
| | - Brenna Hall
- College of Public Health, University of Arizona, Tucson, Arizona, United States of America
| | - Hongseok Ko
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, United States of America
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Allen PS, Finch-Boekweg H, Meyer SE. A proposed mechanism for high pathogen-caused mortality in the seed bank of an invasive annual grass. FUNGAL ECOL 2018. [DOI: 10.1016/j.funeco.2018.07.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Beckstead J, Meyer SE, Ishizuka TS, McEvoy KM, Coleman CE. Lack of Host Specialization on Winter Annual Grasses in the Fungal Seed Bank Pathogen Pyrenophora semeniperda. PLoS One 2016; 11:e0151058. [PMID: 26950931 PMCID: PMC4780786 DOI: 10.1371/journal.pone.0151058] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 02/22/2016] [Indexed: 12/01/2022] Open
Abstract
Generalist plant pathogens may have wide host ranges, but many exhibit varying degrees of host specialization, with multiple pathogen races that have narrower host ranges. These races are often genetically distinct, with each race causing highest disease incidence on its host of origin. We examined host specialization in the seed pathogen Pyrenophora semeniperda by reciprocally inoculating pathogen strains from Bromus tectorum and from four other winter annual grass weeds (Bromus diandrus, Bromus rubens, Bromus arvensis and Taeniatherum caput-medusae) onto dormant seeds of B. tectorum and each alternate host. We found that host species varied in resistance and pathogen strains varied in aggressiveness, but there was no evidence for host specialization. Most variation in aggressiveness was among strains within populations and was expressed similarly on both hosts, resulting in a positive correlation between strain-level disease incidence on B. tectorum and on the alternate host. In spite of this lack of host specialization, we detected weak but significant population genetic structure as a function of host species using two neutral marker systems that yielded similar results. This genetic structure is most likely due to founder effects, as the pathogen is known to be dispersed with host seeds. All host species were highly susceptible to their own pathogen races. Tolerance to infection (i.e., the ability to germinate even when infected and thereby avoid seed mortality) increased as a function of seed germination rate, which in turn increased as dormancy was lost. Pyrenophora semeniperda apparently does not require host specialization to fully exploit these winter annual grass species, which share many life history features that make them ideal hosts for this pathogen.
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Affiliation(s)
- Julie Beckstead
- Department of Biology, Gonzaga University, Spokane, Washington, 99258, United States of America
| | - Susan E. Meyer
- USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, Provo, UT 84606, United States of America
- * E-mail:
| | - Toby S. Ishizuka
- Department of Biology, Gonzaga University, Spokane, Washington, 99258, United States of America
| | - Kelsey M. McEvoy
- Department of Biology, Gonzaga University, Spokane, Washington, 99258, United States of America
| | - Craig E. Coleman
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84602, United States of America
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Finch-Boekweg H, Gardner JS, Allen PS, Geary B. Postdispersal Infection and Disease Development of Pyrenophora semeniperda in Bromus tectorum Seeds. PHYTOPATHOLOGY 2016; 106:236-243. [PMID: 26645644 DOI: 10.1094/phyto-09-15-0229-r] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The Ascomycete fungus, Pyrenophora semeniperda, attacks a broad range of cool-season grasses. While leaf and predispersal infection of seeds (i.e., florets containing caryopses) have been previously characterized, little is known about the pathogenesis of mature seeds following dispersal. In this study, we examined infection and disease development of P. semeniperda on dormant seeds of Bromus tectorum. Inoculated seeds were hydrated at 20°C for up to 28 days. Disease development was characterized using scanning electron and light microscopy. P. semeniperda conidia germinated on the seed surface within 5 to 8 h. Hyphae grew on the seed surface and produced extracellular mucilage that eventually covered the seed. Appressoria formed on the ends of hyphae and penetrated through the lemma and palea, stomatal openings, and broken trichomes. The fungus then catabolized the endosperm, resulting in a visible cavity by 8 days. Pathogenesis of the embryo was associated with progressive loss of cell integrity and proliferation of mycelium. Beginning at approximately day 11, one to several stromata (approximately 150 μm in diameter and up to 4 mm in length) emerged through the lemma and palea. Degradation of embryo tissue was completed near 14 days. Conidiophores produced conidia between 21 and 28 days and often exhibited "Y-shaped" branching. This characterization of disease development corrects previous reports which concluded that P. semeniperda is only a weak seed pathogen with infection limited to the outermost seed tissues. In addition, the time required for disease development explains why infected dormant or slow-germinating seeds are most likely to experience mortality.
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Affiliation(s)
- Heather Finch-Boekweg
- First, third, and fourth authors: Brigham Young University, Department of Plant and Wildlife Sciences, Provo, UT 84602; and second author: Brigham Young University, Department of Biology, Provo, UT 84602
| | - John S Gardner
- First, third, and fourth authors: Brigham Young University, Department of Plant and Wildlife Sciences, Provo, UT 84602; and second author: Brigham Young University, Department of Biology, Provo, UT 84602
| | - Phil S Allen
- First, third, and fourth authors: Brigham Young University, Department of Plant and Wildlife Sciences, Provo, UT 84602; and second author: Brigham Young University, Department of Biology, Provo, UT 84602
| | - Brad Geary
- First, third, and fourth authors: Brigham Young University, Department of Plant and Wildlife Sciences, Provo, UT 84602; and second author: Brigham Young University, Department of Biology, Provo, UT 84602
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Community Ecology of Fungal Pathogens on Bromus tectorum. SPRINGER SERIES ON ENVIRONMENTAL MANAGEMENT 2016. [DOI: 10.1007/978-3-319-24930-8_7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Barth CW, Meyer SE, Beckstead J, Allen PS. Hydrothermal time models for conidial germination and mycelial growth of the seed pathogen Pyrenophora semeniperda. Fungal Biol 2015; 119:720-30. [PMID: 26228560 DOI: 10.1016/j.funbio.2015.04.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2014] [Revised: 03/27/2015] [Accepted: 04/13/2015] [Indexed: 11/27/2022]
Abstract
Population-based threshold models using hydrothermal time (HTT) have been widely used to model seed germination. We used HTT to model conidial germination and mycelial growth for the seed pathogen Pyrenophora semeniperda in a novel approach to understanding its interactions with host seeds. Germination time courses and mycelial growth rates for P.semeniperda were measured on PDA amended to achieve a series of five water potentials (ca. 0 to -6 MPa) at six constant temperatures (5-30 °C). Conidial germination was described with alternative population-based models using constant or variable base and maximum temperature and water potential parameters. Mycelial growth was modeled as a continuous, linear process with constant base temperature and base water potential. Models based on HTT showed reasonable fit to germination and growth rate data sets. The best-fit conidial germination model (R(2) = 0.859) was based on variable base and maximum temperature as a function of water potential. The good fit of the linear mycelial growth model (R(2) = 0.916) demonstrated the utility of HTT for modeling continuous as well as population-based processes. HTT modeling may be a useful approach to the quantification of germination and growth processes in a wide range of filamentous fungi.
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Affiliation(s)
- Connor W Barth
- Department of Biology, Gonzaga University, 502 E. Boone Ave., Spokane, WA 99202, USA.
| | - Susan E Meyer
- US Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, 735 North 500 East, Provo, UT 84606, USA.
| | - Julie Beckstead
- Department of Biology, Gonzaga University, 502 E. Boone Ave., Spokane, WA 99202, USA.
| | - Phil S Allen
- Department of Plant and Wildlife Sciences, 4105A LSB, Brigham Young University, Provo, UT 84602, USA.
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Climatic variation and seed persistence: freeze–thaw cycles lower survival via the joint action of abiotic stress and fungal pathogens. Oecologia 2015; 179:609-16. [DOI: 10.1007/s00442-015-3369-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 06/03/2015] [Indexed: 10/23/2022]
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