Exploring Nonhost Resistance in a Model Legume, Medicago truncatula Against Asian Soybean Rust.

Asian Soybean Rust (ASR), caused by Phakopsora pachyrhizi, is an economically important disease of soybean and it is considered as a major threat for future food security. In the past, few resistance genes that confer resistance against ASR have been identified and deployed in soybean cultivars but due to heterogeneous population and high diversity among P. pachyrhizi races, the host resistance is often short lived. Compared to host resistance, nonhost resistance is more durable. Nonhost resistance is resistance exhibited by a plant species against a particular pathogen. Medicago truncatula, a model legume species, is a nonhost to P. pachyrhizi and shows incompatible interactions with this fungus. To better understand nonhost resistance aginst ASR, we performed forward genetics screening of ca. 2,500 M. truncatula Tnt1 insertion lines and identified several mutants with altered response to ASR. These mutants include phenotypes such as enhanced penetration of rust (epr), sporulation of soybean rust (spr) which is normally rare on M. truncatula, enhanced cell death (ecd) upon rust inoculation and inhibition of rust germ tube (irg).  Further characterization of some of these mutants and the mutated gene responsible for the phenotype will be presented.