Abstract
BackgroundSwitchgrass rust, caused by Puccinia emaculata, is an important disease of switchgrass, a potential biofuel crop in the United States. In severe cases, switchgrass rust has the potential to significantly affect biomass yield. In an effort to identify novel sources of resistance against switchgrass rust, we explored nonhost resistance against P. emaculata by characterizing its interactions with six monocot nonhost plant species. We also studied the genetic variations for resistance among Brachypodium inbred accessions and the involvement of various defense pathways in nonhost resistance of Brachypodium.ResultsWe characterized P. emaculata interactions with six monocot nonhost species and identified Brachypodium distachyon (Bd21) as a suitable nonhost model to study switchgrass rust. Interestingly, screening of Brachypodium accessions identified natural variations in resistance to switchgrass rust. Brachypodium inbred accessions Bd3-1 and Bd30-1 were identified as most and least resistant to switchgrass rust, respectively, when compared to tested accessions. Transcript profiling of defense-related genes indicated that the genes which were induced in Bd21after P. emaculata inoculation also had higher basal transcript abundance in Bd3-1 when compared to Bd30-1 and Bd21 indicating their potential involvement in nonhost resistance against switchgrass rust.ConclusionIn the present study, we identified Brachypodium as a suitable nonhost model to study switchgrass rust which exhibit type I nonhost resistance. Variations in resistance response were also observed among tested Brachypodium accessions. Brachypodium nonhost resistance against P. emaculata may involve various defense pathways as indicated by transcript profiling of defense related genes. Overall, this study provides a new avenue to utilize novel sources of nonhost resistance in Brachypodium against switchgrass rust.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0502-9) contains supplementary material, which is available to authorized users.
Highlights
Switchgrass rust, caused by Puccinia emaculata, is an important disease of switchgrass, a potential biofuel crop in the United States
In an effort to identify sources of Nonhost resistance (NHR) against switchgrass rust, we tested six different monocot plant species belonging to the BEP and PACCMAD clades for their response to P. emaculata inoculation (Additional file 5)
Analyses of Brachypodium-switchgrass rust interactions suggest type I NHR responses exhibited by Brachypodium
Summary
Switchgrass rust, caused by Puccinia emaculata, is an important disease of switchgrass, a potential biofuel crop in the United States. In an effort to identify novel sources of resistance against switchgrass rust, we explored nonhost resistance against P. emaculata by characterizing its interactions with six monocot nonhost plant species. Urediniospores of P. emaculata collected from ornamental switchgrass were found to have greater virulence than urediniospores collected from agronomic switchgrass plots [10] These variations in virulence of wind-borne rust urediniospores pose a great threat to monoculture of switchgrass varieties in new geographical areas. Genetic variations in switchgrass germplasm can be exploited to find sources of host resistance, but host resistance is generally less durable due to the fact that variations exist in rust pathogen isolates
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