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The Problem Every year millions of tons of agrichemical pesticides are applied to soils in and around aquatic ecosystems that eventually pollute rivers, streams, lakes, wetlands, and municipal water supplies. In addition, agricultural soils are routinely sterilized with methyl bromide, a chemical that destroys atmospheric ozone and increases the amount of ultraviolet light radiation which results in the degradation of aquatic systems. In an attempt to decrease pesticide pollution of aquatic ecosystems, we have begun a project to develop biological control agents to protect plants against fungal diseases. Objectives The 5-year research goal of the Fisheries and Aquatic Resources Program addressed is to understand relationships between and among aquatic species habitats. provide science for restoring and maintaining declining species and their required habitat. The subtask has three objectives: (1) understanding how fungi cause disease; (2) understanding how plants that are symbiotic with certain fungi are resistant to fungal diseases; and (3) developing an effective biological control system to protect plants against fungal diseases. Methodology
To begin understanding how fungi cause disease in plants we have induced a number of gene disruption mutations in the genome of the filamentous fungal cucurbit pathogen Colletotrichum magna. The mutations eliminated the ability of this fungus to cause disease but had no effect on the infection and colonization processes. Plants colonized with these mutants are protected against root diseases caused by a variety of other fungi. The pathogenicity genes responsible for the mutations are currently being cloned and sequenced to determine their function and when they are expressed during the disease process. In addition, extensive genetic analyses are being performed with the mutants to determine gene dominance among the mutated pathogenicity genes. Once these analyses are completed, the genetic complexity of pathogenicity will be better understood and the construction of efficient biological control isolates will ensue. The second aspect of this research involves understanding the response of symbiotic plants to virulent isolates and non-pathogenic mutants of this fungus. The activity of several biochemical pathways and the expression of several genes associated with the plant defense response are being analyzed. Several plant hosts are being used for this study to determine if the mechanism of disease resistance is universal and predictive. As the genetic analyses are completed on different non-pathogenic mutants, they will be incorporated into this study to determine if the plant response is the same to different phenotypic mutants. The third aspect of this project involves testing the non-pathogenic mutants for their ability to protect plants under field conditions. These experiments will involve screening mutant colonized and uncolonized watermelon, squash, tomato and strawberry plants in pathogen infested fields in Oklahoma, Florida, and California. Data will be collected for plant survival, growth rates, fruit yields, and fruit production time. This will allow us to assess if there are metabolic costs to the symbiotic association between non-pathogenic mutants and plant hosts, and to determine the feasibility of using this type of system to decrease pesticide contamination of ground water. Future field trials will focus on agricultural runoff associated with heavily polluted aquatic systems such as the Salton Sea in the Imperial Valley of California and Klamath lake in Oregon. Highlights and Key Findings
Non-pathogenic gene disruption mutants have been isolated that express one of four symbiotic lifestyles: mutualism, commensalism, intermediate mutualism and abortive colonization. These lifestyles are based on the ability of symbionts to confer disease protection, drought tolerance, and growth enhancement to plant hosts. Although the physiological basis of drought tolerance and growth enhancement are not yet known, the basis of disease protection has been characterized. Disease protection conferred by the mutualists involves the rapid and strong activation of host defense systems when symbiotic plants are confronted with pathogenic organisms. Several large field trials have been performed to demonstrate that the symbiotic association between plants and non-pathogenic mutants impose no metabolic costs, are maintained throughout the growing season and result in an increase in fruit production. In addition, field tests have indicated that the symbionts are not transmitted between plants in the same field. Field trials are currently underway to test the utility of this form of biological control. Analysis of several natural plant-fungal symbioses has led to the development of a new hypothesis that fungal endophytes allow plants to respond to abiotic stresses. Ecological studies are underway to
07/16/2001 - 160 non-pathogenic gene disruption mutants have been isolated that express one of four symbiotic lifestyles: mutualism, commensalism, intermediate mutualism and abortive colonization. These lifestyles are based on the ability of symbionts to confer disease protetion, drought tolerance, and growth enhancement to plant hosts. Althought the physiological basis of drought tolerance and growth enhancement are not yet known, the basis of disease protection has been characterized. Disease protection conferred by the mutualists involves the rapid and strong activation of host defense systems when symbiotic plants are confronted with pathogenic organisms. Several large field trials have been performed to demonstrate that the symbiotic association between plants and non-pathogenic mutants impose no metabolic costs, are maintained throughout the growing season and result in an increase in fruit production. In addition, field tests have indicated that the symbionts are not transmitted between plants in the same field. Field trials are currently underway to test the utility of this form of biological control. Analysis of several natural plant-fungal symbioses has led to the development of a new hypothesis that fungal endophytes allow plants to respond to abiotic stresses. Ecological studies are underway to determine the validity of this hypothesis and to determine the utility of symbiosis in habitat restoration efforts and decreasing irrigation needs in agriculture. Where Are We Headed In 2003
In 2003 the crop-specific FSL mutants will be tested for the ability to protect plants against fungal diseases, confer drought tolerance, and increase growth and yields. The FSL gene will be further characterized by sequence, hybridization, and expression analysis. Experiments will be initiated to begin analyzing native plant species for the presence and expression of the FSL gene to determine if it can be used to monitor the success of habitat restoration efforts. Project Contact Rusty Rodriguez Email: rusty_rodriguez@usgs.gov Publications |
