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J. Alejandro Rojas

Bio: J. Alejandro Rojas is an academic researcher from University of Arkansas. The author has contributed to research in topics: Oomycete & Phytophthora. The author has an hindex of 6, co-authored 7 publications receiving 158 citations. Previous affiliations of J. Alejandro Rojas include Duke University & Michigan State University.
Topics: Oomycete, Phytophthora, Pythium, Edaphic, Ecosystem

Papers
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Journal ArticleDOI
TL;DR: This study provides a comprehensive characterization of oomycete species present in soybean seedling roots in the major production areas in the United States and Ontario, Canada and provides a basis for disease management and breeding programs.
Abstract: Oomycete pathogens are commonly associated with soybean root rot and have been estimated to reduce soybean yields in the United States by 1.5 million tons on an annual basis. Limited information exists regarding the frequency and diversity of oomycete species across the major soybean-producing regions in North America. A survey was conducted across 11 major soybean-producing states in the United States and the province of Ontario, Canada. In 2011, 2,378 oomycete cultures were isolated from soybean seedling roots on a semiselective medium (CMA-PARPB) and were identified by sequencing of the internal transcribed spacer region of rDNA. Sequence results distinguished a total of 51 Pythium spp., three Phytophthora spp., three Phytopythium spp., and one Aphanomyces sp. in 2011, with Pythium sylvaticum (16%) and P. oopapillum (13%) being the most prevalent. In 2012, the survey was repeated, but, due to drought conditions across the sampling area, fewer total isolates (n = 1,038) were collected. Additionally, in 2012, a second semiselective medium (V8-RPBH) was included, which increased the Phytophthora spp. isolated from 0.7 to 7% of the total isolates. In 2012, 54 Pythium spp., seven Phytophthora spp., six Phytopythium spp., and one Pythiogeton sp. were recovered, with P. sylvaticum (14%) and P. heterothallicum (12%) being recovered most frequently. Pathogenicity and virulence were evaluated with representative isolates of each of the 84 species on soybean cv. Sloan. A seed-rot assay identified 13 and 11 pathogenic species, respectively, at 13 and 20°C. A seedling-root assay conducted at 20°C identified 43 species as pathogenic, having a significantly detrimental effect on the seedling roots as compared with the noninoculated control. A total of 15 species were pathogenic in both the seed and seedling assays. This study provides a comprehensive characterization of oomycete species present in soybean seedling roots in the major production areas in the United States and Ontario, Canada and provides a basis for disease management and breeding programs.

70 citations

Journal ArticleDOI
TL;DR: It is suggested that oomycete species composition across geographical locations of soybean production is affected by a combination of environmental and edaphic conditions.
Abstract: Soybean (Glycine max (L.) Merr.) is produced across a vast swath of North America, with the greatest concentration in the Midwest. Root rot diseases and damping-off are a major concern for production, and the primary causal agents include oomycetes and fungi. In this study, we focused on examination of oomycete species distribution in this soybean production system and how environmental and soil (edaphic) factors correlate with oomycete community composition at early plant growth stages. Using a culture-based approach, 3,418 oomycete isolates were collected from 11 major soybean-producing states and most were identified to genus and species using the internal transcribed spacer region of the ribosomal DNA. Pythium was the predominant genus isolated and investigated in this study. An ecology approach was taken to understand the diversity and distribution of oomycete species across geographical locations of soybean production. Metadata associated with field sample locations were collected using geographical...

60 citations

Journal ArticleDOI
TL;DR: Multiplex qPCR and isothermal RPA (recombinase polymerase amplification) assays were developed using a hierarchical approach to detect Phytophthora spp.
Abstract: Phytophthora root rot of soybean, caused by Phytophthora sojae, is one of the most important diseases in the Midwestern United States, and is estimated to cause losses of up to 1.2 million metric tons per year. Disease may also be caused by P. sansomeana; however, the prevalence and damage caused by this species is not well known, partly due to limitations of current diagnostic tools. Efficient, accurate, and sensitive detection of pathogens is crucial for management. Thus, multiplex qPCR and isothermal RPA (recombinase polymerase amplification) assays were developed using a hierarchical approach to detect these Phytophthora spp. The assays consist of a genus-specific probe and two species-specific probes that target the atp9-nad9 region of the mitochondrial genome that is highly specific for the genus Phytophthora. The qPCR approach multiplexes the three probes and a plant internal control. The RPA assays run each probe independently with a plant internal control multiplexed in one amplification, obtaining a result in as little as 20 mins. The multicopy mitochondrial genome provides sensitivity with sufficient variability to discern among different Phytophthora spp. The assays were highly specific when tested against a panel of 100 Phytophthora taxa and range of Pythium spp. The consistent detection level of the assay was 100 fg for the qPCR assay and 10 pg for the RPA assay. The assays were validated on symptomatic plants collected from Michigan (U.S.) and Ontario (Canada) during the 2013 field season, showing correlation with isolation. In 2014, the assays were validated with samples from nine soybean producing states in the U.S. The assays are valuable diagnostic tools for detection of Phytophthora spp. affecting soybean.

41 citations

Journal ArticleDOI
TL;DR: Metatranscriptomic studies revealed that these fungi impacted rhizophytic and endophytic activities in P. trichocarpa and induced shifts in soil and root microbial communities.
Abstract: Mortierella and Ilyonectria genera include common species of soil fungi that are frequently detected as root endophytes in many plants, including Populus spp. However, the ecological roles of these and other endophytic fungi with respect to plant growth and function are still not well understood. The functional ecology of two key taxa from the P. trichocarpa rhizobiome, M. elongata PMI93 and I. europaea PMI82, was studied by coupling forest soil bioassays with environmental metatranscriptomics. Using soil bioassay experiments amended with fungal inoculants, M. elongata was observed to promote the growth of P. trichocarpa. This response was cultivar independent. In contrast, I. europaea had no visible effect on P. trichocarpa growth. Metatranscriptomic studies revealed that these fungi impacted rhizophytic and endophytic activities in P. trichocarpa and induced shifts in soil and root microbial communities. Differential expression of core genes in P. trichocarpa roots was observed in response to both fungal species. Expression of P. trichocarpa genes for lipid signaling and nutrient uptake were upregulated, and expression of genes associated with gibberellin signaling were altered in plants inoculated with M. elongata, but not I. europaea. Upregulation of genes for growth promotion, downregulation of genes for several leucine-rich repeat receptor kinases, and alteration of expression of genes associated with plant defense responses (e.g., jasmonic acid, salicylic acid, and ethylene signal pathways) also suggest that M. elongata manipulates plant defenses while promoting plant growth.

40 citations

Journal ArticleDOI
14 Jul 2020
TL;DR: Hypotheses on how effects of introduced and invasive EM fungi may depend on interactions between soil N availability in the exotic range and EM fungal traits are developed and tested.
Abstract: Introductions and invasions by fungi, especially pathogens and mycorrhizal fungi, are widespread and potentially highly consequential for native ecosystems, but may also offer opportunities for linking microbial traits to their ecosystem functions. In particular, treating ectomycorrhizal (EM) invasions, i.e., co-invasions by EM fungi and their EM host plants, as natural experiments may offer a powerful approach for testing how microbial traits influence critical ecosystem functions. Forests dominated by EM symbiosis have unique biogeochemistry whereby the extracellular compoundssecretions of EM plants and fungi may also alteraffect carbon (C) and nutrient cycling; moreover, particular lineages of EM fungi have unique functional traits. EM invasions may therefore alter the biogeochemistry of the native landscapes ecosystems they invade, especially nitrogen (N) and carbon (C) cycling. By identifying “response traits” that favor the success of fungi in introductions and invasions (e.g., spore dispersal and germination) and their correlations with “effect traits” (e.g., nutrient-cycling enzymes) that can alter N and C cycling (and affect other coupled elemental cycles), one may be able to predict the ecosystem functional consequences for ecosystems of fungal invasions using biogeochemistry models that incorporate fungal traits. Here, we review what is already known about how EM fungal community composition, traits, and ecosystem functions vary amongdiffer between native and exotic populations, focusing on the example of EM fungi associated with species of Pinus introduced from the Northern into the Southern Hemisphere. We develop hypotheses on how effects of introduced and invasive EM fungi may depend on interactions between exotic soil N availability in the exotic range and EM fungal traits. We discuss how such hypotheses could be tested by utilizing pine Pinus introductions and invasions as a model system, especially when combined with controlled laboratory experiments. Finally, we illustrate how ecosystem modeling can be used to link fungal traits to their consequences for ecosystem N and C cycling in the context of biological invasions, and we highlight exciting avenues for future directions in understanding EM invasion.

20 citations


Cited by
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TL;DR: Changes in ecosystems complexity- functioning relationships could diminish the stability, resistance and resilience of managed terrestrial ecosystems, and may jeopardize important food and fibre sources, and ability of natural ecosystems both to provide natural resources, and to remove pollutants from atmosphere.
Abstract: Over the past 50 years, humans have altered their environment to a significant extent, although human well-being is dependent on ecosystem functioning. Ecosystems are particularly affected by unsustainable use of resources, such as, food, water, and timber. Ecosystem functions depend on water, carbon, and other nutrients cycles. Human activities have modified these cycles in a number of way. Use of ecosystems for recreation, spiritual enrichment, cultural purposes, and for other short term benefits is growing continuously, although ecosystem capacity to provide such services has reported to be declined significantly. Human well-being depends on material welfare, health, good social relations, security and freedom, which are affected by changes in ecosystem services. Intensive ecosystem use often produces short-term advantage. Poverty level remains high in more than one billion people, who are dependent on ecosystems with an income of less than $1 per day as reported elsewhere. Regions including some parts of Africa, Asia and Latin America have the greatest ecosystemrelated problems and are facing developmental challenges. Habitat change occurs, for instance, when the area of land used for agriculture or cities is expanded. Instability and unproductivity including desertification, water logging, mineralization and many other unwanted outcomes throughout the world are continuing. Habitat fragmentation by roads, canals, power lines limits the species potential for dispersal and colonization. Indirect drivers, like changes in human population, economic activity and technology as well as socio-political and cultural factors affect ecosystems by influencing direct drivers. World climate has changed and continues to change, affecting temperature, rainfall and sea levels. Intensive fertilizer use has polluted ecosystems. Climate change and high nutrient levels in water are becoming increasing problems. Ecosystem management for shortterm benefits is increasing. Loss of biodiversity makes it difficult for ecosystems to recover from damage. Once an ecosystem has undergone an abrupt change, recovery to the original state is slow, costly, and sometimes impossible. Changes in ecosystems complexity- functioning relationships could diminish the stability, resistance and resilience of managed terrestrial ecosystems, and may jeopardize important food and fibre sources, and ability of natural ecosystems both to provide natural resources, and to remove pollutants from atmosphere. Ecological complexity and ecosystem functioning depend on factors that govern species coexistence. Complexity of landscapes is determined by number of ecosystem types, their characteristics, their sizes and shapes, and associated connectivity. Complexity at this scale would have large consequences on regional to global scale processes. Presence and arrangement of keystone ecosystem types, such as, wetlands often determine total carbon and nitrogen balance of a region. Changes in average or extreme environmental events and intense land use management are believed to increase species extinction rate in isolated habitat fragments. Loss of key species, such as, top predators, fruit dispersers and pollinators from habitat may severely disrupt ecosystems functioning. Land use changes due to expanding urbanization, concomitant landscape fragmentation and intensification of production systems. Such change results in transformation of an ecosystem, form one state to another state, via a transition phase. The combined value of 17 ecosystem services has been reported in the estimated range of US$16-54 trillion per year by Costanza and others. About 30% of modern medicines are developed from plants and animals, and 10 of the world's 25 topselling drugs in 1997 were reported to be derived from natural sources. Global market value of pharmaceuticals derived from genetic resources is estimated at US $ 75 000-150 000 million annually. Some 75% of the world's populations rely for health care on traditional medicines, which are derived directly from natural sources as recorded elsewhere. Socio-economic development of human civilization and human well-being depends on long-term health of environment including ecosystems. Environmental problems are generally addressed in isolation, but practically such problems are interrelated, and originate from the root cause of unsustainable development. Damage to natural ecosystems and release of environmental pollutants must be minimized for protecting natural ecosystem, and human well-being.

559 citations

01 Mar 2005
TL;DR: The College of Pharmacy is committed to maintaining a community which recognizes and values the inherent worth and dignity of every person; fosters tolerance, sensitivity, understanding, and mutual respect among its members; and encourages each individual to strive to reach his or her own potential.
Abstract: As a unit within Purdue University, the College of Pharmacy “is committed to maintaining a community which recognizes and values the inherent worth and dignity of every person; fosters tolerance, sensitivity, understanding, and mutual respect among its members; and encourages each individual to strive to reach his or her own potential. In pursuit of its goal of academic excellence, the University seeks to develop and nurture diversity. The University believes that diversity among its many members strengthens the institution, stimulates creativity, promotes the exchange of ideas, and enriches campus life.”1

481 citations

Journal ArticleDOI
TL;DR: An overview of the enormous morphological, taxonomical and functional diversity of soil protists is provided, and current challenges and opportunities in soil protistology are discussed.
Abstract: Protists include all eukaryotes except plants, fungi and animals. They are an essential, yet often forgotten, component of the soil microbiome. Method developments have now furthered our understanding of the real taxonomic and functional diversity of soil protists. They occupy key roles in microbial foodwebs as consumers of bacteria, fungi and other small eukaryotes. As parasites of plants, animals and even of larger protists, they regulate populations and shape communities. Pathogenic forms play a major role in public health issues as human parasites, or act as agricultural pests. Predatory soil protists release nutrients enhancing plant growth. Soil protists are of key importance for our understanding of eukaryotic evolution and microbial biogeography. Soil protists are also useful in applied research as bioindicators of soil quality, as models in ecotoxicology and as potential biofertilizers and biocontrol agents. In this review, we provide an overview of the enormous morphological, taxonomical and functional diversity of soil protists, and discuss current challenges and opportunities in soil protistology. Research in soil biology would clearly benefit from incorporating more protistology alongside the study of bacteria, fungi and animals.

297 citations

Journal ArticleDOI
TL;DR: A broad synthesis of the ecological and agricultural literature focused on seed-microbe interactions as a means of better understanding how these interactions may ultimately influence plant ecology, health, and productivity in both natural and agricultural systems is presented.
Abstract: The development and dispersal of seeds as well as their transition to seedlings represent perhaps the most critical stages of a plant’s life cycle The endophytic and epiphytic microbial interactions that take place in, on, and around seeds during these stages of the plant’s life cycle may have profound impacts on plant ecology, health, and productivity While our understanding of the seed microbiota has lagged far behind that of the rhizosphere and phyllosphere, many advances are now being made This review explores the microbial associations with seeds through various stages of the plant life cycle, beginning with the earliest stages of seed development on the parent plant and continuing through the development and establishment of seedlings in soil This review represents a broad synthesis of the ecological and agricultural literature focused on seed-microbe interactions as a means of better understanding how these interactions may ultimately influence plant ecology, health, and productivity in both natural and agricultural systems Our current understanding of seed-microbe associations will be discussed, with an emphasis on recent findings that specifically highlight the emerging contemporary understanding of how seed-microbe associations may ultimately impact plant health and productivity The diversity and dynamics of seed microbiomes represent the culmination of complex interactions with microbes throughout the plant life cycle The richness and dynamics of seed microbiomes is revealing exciting new opportunities for research into plant-microbe interactions Often neglected in plant microbiome studies, the renaissance of inquiry into seed microbiomes is offering exciting new insights into how the diversity and dynamics of the seed microbiome with plant and soil microbiomes as well as the microbiomes of dispersers and pollinators It is clear that the interactions taking place in and around seeds indeed have significant impacts on plant health and productivity in both agricultural and natural ecosystems

261 citations

Journal ArticleDOI
TL;DR: The growing interest in the application of Mortierella spp.
Abstract: In the most recent scientific reports based on the DNA or RNA-analyses a widespread presence of the filamentous fungi, Mortierella in various environments has been shown. Some strains of this genus belong to the plant growth-promoting fungi (PGPF) and are found in the bulk soil, rhizosphere and plants tissues. These microorganisms are also often found in the extremely hostile environments, responsible for improving access to the bioavailable forms of P and Fe in the soils, the synthesis of phytohormones and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and last but not least the protection of agricultural plants from pathogens. Furthermore, earlier reports classified Mortierella spp. as the saprotrophic microorganisms isolated from the forest litter, and nowadays their status as a very valuable decomposers in the agricultural soils was confirmed. The key features like the ability to survive under very unfavorable environmental conditions and the utilization of carbon sources contained in polymers like cellulose, hemicellulose, chitin make these fungi efficient as the agricultural inoculants. The growing interest in the application of Mortierella spp. is mainly due to the potential use of this genus in the increase of the nutrient uptake efficiency, positive effect in crop protection against adverse conditions, and reduction of chemical fertilizers and pesticides applied. Moreover, activities of Mortierella species selected from the wild or cultivated plants influence the soil microbiota and support the performance of the beneficial microorganisms enhancing significantly crop yield.

109 citations