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Positional Cloning and Characterization of RCT1, an Anthracnose Resistance Gene in Medicago
Department of Plant and Soil Sciences
Anthracnose is one of the most destructive diseases of alfalfa in the United States. The disease can cause up to 25-30% yield loss in susceptible alfalfa varieties as well as losses in plant stand and vigor. The same pathogen also causes anthracnose in a number of closely related forage legumes such as annual medic, red clover, and white clover. Improved understanding of anthracnose resistance mechanisms will aid in the development of resistant alfalfa cultivars and positively impact the sustainability of U.S. agriculture. Unfortunately, the biological characteristics of cultivated alfalfa (polyploidy, out-crossing, and population diversity) severely limit the ability to carry out genetic analyses of agronomically important traits, including disease resistance. However, the model legume Medicago truncatula, a close relative of alfalfa, has the potential to serve as a surrogate species for genetic analysis of many economically important alfalfa traits and to provide new sources of host resistance.
Thus, the goal is to use of M. truncatula as a model system to map and clone the counterparts of agronomically important genes in alfalfa, in particular, disease resistance genes. The research plan described in this proposal is to clone an anthracnose host resistance gene in Medicago truncatula. This gene will provide new tools for alfalfa improvement.
2011 Project Description
Alfalfa is economically the most important forage legume worldwide. A recurrent challenge to alfalfa production is the significant yield loss caused by disease. Although knowledge of molecular mechanisms underlying host resistance should facilitate the genetic improvement of alfalfa, the acquisition of such knowledge is hampered by alfalfa's tetrasomic inheritance and outcrossing nature.
However, alfalfa is congeneric with the reference legume Medicago truncatula, providing an opportunity to use M. truncatula as a surrogate to clone the counterparts of many agronomically important genes in alfalfa. In particular, the high degree of sequence identity and remarkably conserved genome structure and function between the two species enables M. truncatula genes to be used directly in alfalfa improvement.
We have cloned the RCT1, a host resistance (R) gene in M. truncatula that confers resistance to multiple races of Colletotrichum trifolii, a hemibiotrophic fungal pathogen that causes anthracnose disease of alfalfa.
RCT1 is a member of the Toll-interleukin-1 receptor/nucleotide-binding site/leucine-rich repeat (TIR-NBS-LRR) class of plant R genes and confers broad-spectrum anthracnose resistance when transferred into susceptible alfalfa plants. Thus, RCT1 provides a novel resource to develop anthracnose-resistant alfalfa cultivars and contributes to our understanding of host resistance against the fungal genus Colletotrichum. This work demonstrates the potential of using M. truncatula genes for genetic improvement of alfalfa.