Pythiums as Plant Pathogens
01 Sep 1973-Annual Review of Phytopathology (Annual Reviews 4139 El Camino Way, P.O. Box 10139, Palo Alto, CA 94303-0139, USA)-Vol. 11, Iss: 1, pp 77-98
TL;DR: This review will concentrate on examples of the readily available literature of the past 50 years and will emphasize the pathology of the genus Pythium, with only brief treatment of other aspects such as taxonomy and control.
Abstract: The genus Pythium includes a number of readily recognized species with wide distributions and host ranges. The taxonomic position of the genus and its relationship to other Phycomycetes were well established during the latter part of the 19th century. In the early 1900s pathologists found Pythium spp. consistently associated with root diseases and it soon became apparent that these fungi were important plant pathogens. Certainly, while 1),ot all isolates of Pythium species are capable of causing diseases of plants, many are soil borne pathogens that cause serious economic loss on a wide variety of hosts, while others are more limited in host and geographic range or affect plants only under special environmental conditions. New species are being discov ered as pathologists investigate soil organisms associated with plant growth problems. Rands & Dopp (123) in their classic investigation of sugarcane root dis eases established the symptoms and determined the conditions needed for these fungi to become destructive. This work, and others of a similar nature, are part of the extensive literature on diseases caused by species of Pythium. This review will concentrate on examples of the readily available literature of the past 50 years and will emphasize the pathology of the genus, with only brief treatment of other aspects such as taxonomy and control. It will be con fined to Pythium spp. as they affect economic plants and will not deal with those affecting algae, other marine plants, fungi, and unusual hosts.
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TL;DR: In this article, a soil fungus, Pythium irregulare, was found to blight jar1-1, an Arabidopsis jasmonate response mutant that exhibits reduced sensitivity to methyl jamasmonate, indicating that increased susceptibility was due to the lesion in the JAR1 locus.
Abstract: Jasmonic acid has properties of a plant hormone, including the induction of specific genes associated with plant defense. We previously described jar1-1, an Arabidopsis jasmonate response mutant that exhibits reduced sensitivity to methyl jasmonate. We have further characterized this mutant and two new alleles; jar1-2 from a gamma irradiated population, and jar1-4 from a T-DNA mutant population. Seedling root growth in jar1-1 was equally insensitive to methyl jasmonate and jasmonic acid, indicating that the defect was not in the conversion of methyl jasmonate to the acid. None of the jar1 mutants showed an altered sensitivity to auxin, cytokinin, or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, indicating that the lesion does not affect the general uptake or transport of hormones. A soil fungus, Pythium irregulare, was found to blight jar1-1. Cultures of this organism caused the symptoms in all three jar1 mutants but not in wild type, indicating that increased susceptibility was due to the lesion in the JAR1 locus. A fatty acid desaturase triple mutant that is defective in the biosynthesis of jasmonic acid (J. Browse, Washington State University) was also susceptible, confirming that jasmonate is involved in resistance. The jar1-1 locus was mapped to the lower end of chromosome 2, about 11.4 cM from as1 and 1.6 cM from cer8. These results establish that jasmonate signaling plays an important role in resistance to soil micro-organisms in plants.
361 citations
TL;DR: Information on the ecology and biological control of plant pathogenic Pythium species is reviewed with the premise that a clear understanding of the ecology of the pathogen will assist in the development of efficacious biocontrol agents.
Abstract: Soilborne root diseases caused by plant pathogenic Pythium species cause serious losses in a number of agricultural production systems, which has led to a considerable effort devoted to the development of biological agents for disease control. In this article we review information on the ecology and biological control of these pathogens with the premise that a clear understanding of the ecology of the pathogen will assist in the development of efficacious biocontrol agents. The lifecycles of the pathogens and etiology of host infection also are reviewed, as are epidemiological concepts of inoculum-disease relationships and the influence of environmental factors on pathogen aggressiveness and host susceptibility. A number of fungal and bacterial biocontrol agents are discussed and parallels between their ecology and that of the target pathogens highlighted. The mechanisms by which these microbial agents suppress diseases caused by Pythium spp., such as interference with pathogen survival, disruption of the...
357 citations
Cites background from "Pythiums as Plant Pathogens"
...Pythium spp. are the most important pathogens infecting seeds or seedlings before emergence from the soil, resulting in preemergence damping-off (Hendrix and Campbell, 1973)....
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...are the most important pathogens infecting seeds or seedlings before emergence from the soil, resulting in preemergence damping-off (Hendrix and Campbell, 1973)....
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...Additional background material on the biology and ecology of the genus Pythium may be found in Hendrix and Campbell (1973, 1983) or the proceedings of the Symposium on the genus Pythium (1974), on pathogenesis and host specificity in Martin (1995), on zoospore development in Deacon and Donaldson…...
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...Numerous examples of the influence of temperature on disease severity have been reported, only some of which are presented here (consult Hendrix and Campbell, 1973, 1983 for additional references)....
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TL;DR: Tobacco plants were transformed with the mutant etr1-1 gene from Arabidopsis, conferring dominant ethylene insensitivity, but these transformants did not slow growth when contacting neighboring plants, hardly expressed defense-related basic pathogenesis-related proteins, and developed spontaneous stem browning.
Abstract: Enhanced ethylene production is an early response of plants to pathogen attack and has been associated with both resistance and susceptibility to disease. Tobacco plants were transformed with the mutant etr1–1 gene from Arabidopsis, conferring dominant ethylene insensitivity. Besides lacking known ethylene responses, these transformants (Tetr) did not slow growth when contacting neighboring plants, hardly expressed defense-related basic pathogenesis-related proteins, and developed spontaneous stem browning. Whereas hypersensitive resistance to tobacco mosaic virus was unimpaired, Tetr plants had lost nonhost resistance against normally nonpathogenic soil-borne fungi.
345 citations
TL;DR: The results of these experiments suggest that the accumulation of species-specific soil pathogens could account for the previous observation of negative feedback on plant growth through changes in the soil community.
Abstract: The effect of soil pathogens on plant communities was investigated using four old-field perennial plant species and five isolates of a pathogenic oomycete in the genus Pythium These Pythium strains were isolated from the roots of two of the plant species, Danthonia spicata and Panicum sphaerocarpon, used in a previous experiment on the consequences of changes in the soil community on plant growth In this previous experiment, Danthonia and Panicum changed the soil community in a manner that reduced their growth relative to that of a third plant species, Anthoxanthum odoratum In the current experiments, we found that inoculation with Pythium reduced overall plant mass and root: shoot ratios, but Danthonia and Panicum were more susceptible to the presence of Pythium than the other two plant species, Anthoxanthum and Plantago lanceolata In addition, Pythium ac- cumulates at different rates on different plant species, with a greater than tenfold higher population observed in association with Panicum compared to Anthoxanthum The results of these experiments suggest that the accumulation of species-specific soil pathogens could account for the previous observation of negative feedback on plant growth through changes in the soil community As negative feedback may act to maintain plant species diversity within a community, these results suggest that soil pathogens may themselves contribute to the maintenance of plant species diversity
275 citations
TL;DR: The discovery of a genetic basis in the host for interactions with a biocontrol agent suggests new opportunities to exploit natural genetic variation in host species to enhance the understanding of beneficial plant-microbe interactions and develop ecologically sound strategies for disease control in agriculture.
Abstract: Plant health depends, in part, on associations with disease-suppressive microflora, but little is known about the role of plant genes in establishing such associations. Identifying such genes will contribute to understanding the basis for plant health in natural communities and to new strategies to reduce dependence on pesticides in agriculture. To assess the role of the plant host in disease suppression, we used a genetic mapping population of tomato to evaluate the efficacy of the biocontrol agent Bacillus cereus against the seed pathogen Pythium torulosum. We detected significant phenotypic variation among recombinant inbred lines that comprise the mapping population for resistance to P. torulosum, disease suppression by B. cereus, and growth of B. cereus on the seed. Genetic analysis revealed that three quantitative trait loci (QTL) associated with disease suppression by B. cereus explained 38% of the phenotypic variation among the recombinant inbred lines. In two cases, QTL for disease suppression by B. cereus map to the same locations as QTL for other traits, suggesting that the host effect on biocontrol is mediated by different mechanisms. The discovery of a genetic basis in the host for interactions with a biocontrol agent suggests new opportunities to exploit natural genetic variation in host species to enhance our understanding of beneficial plant—microbe interactions and develop ecologically sound strategies for disease control in agriculture.
201 citations
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