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An integrated approach to study cotton root rot disease in alfalfa
Phymatotrichum (cotton or Texas) root rot is caused by the broad host range, soilborne fungus Phymatotrichopsis omnivora (Duggar) Hennebert. Phymatotrichum root rot (PRR) is one of most destructive diseases of cotton (Gossypium spp.) and alfalfa (Medicago sativa). The fungus infects most dicotyledonous field crops, causing significant losses of cotton, alfalfa, horticultural trees and shrubs in the southwestern areas of USA, northern Mexico and possibly parts of Asia. However, this fungus does not cause disease in monocotyledonous plants. Symptoms include an expanding tissue collapse (rot) of infected taproots. Above ground, this root rot disease results in vascular discoloration of the stem and rapid wilting of leaves without abscission and eventually the death of the plant. Characteristic mycelial strands of the pathogen are typically present on the root’s surface, aiding diagnosis. The fungus affects numerous crop plants, including alfalfa and cotton. No consistently effective control measures are known. Chemical fumigation methods are not cost-effective for most crops. Interestingly, no genetic resistance has been reported in any of the susceptible field crops.
This project is part of a collaborative project between Noble Foundation, OSU and OU. We are using the model host plant M. truncatula (closely related to alfalfa) to study PRR disease. Unlike alfalfa, which is a tetraploid and obligate outcrossing species, M. truncatula has a simple diploid genome (two sets of eight chromosomes) and can be self-pollinated. M. truncatula is fast emerging as a model legume because of its small genome, which is almost completely sequenced, fast generation time, high transformation efficiency and the availability of Affymetrix gene chips, numerous ecotypes, EMS, fast-neutron and insertional mutants. Most importantly, P. omnivora can cause typical disease symptoms on M. truncatula, and there is a high amount of microsynteny across M. truncatula, alfalfa and other model plant systems. We are currently doing expression profiling using Affymetrix chips to look at differential gene expression during disease development in M. truncatula that will be followed by functional analysis of candidate genes using RNAi or overexpression to identify candidate genes for engineering cultivated alfalfa for PRR resistance. We are screening M. truncatula ecotypes to identify PRR resistant germplasm(s) and transposon-tagged mutants (by both forward and reverse genetics) to identify plant genes involved in Medicago-P. omnivora interactions. This project is funded by a grant to the Consortium for Legume Research from the Oklahoma State Regents for Higher Education.
Publications related to this project:
© 1997-2008 by The Samuel Roberts Noble Foundation, Inc.