Characterization of the Rust Fungus, Puccinia emaculata, and Evaluation of Genetic Variability for Rust Resistance in Switchgrass Populations

Srinivasa Rao Uppalapati,Malay C Saha,Les J Szabo,Shipra Mittal,Desalegn D Serba,Yasuhiro Ishiga,Hem S Bhandari,Joseph H Bouton,Kirankumar S Mysore

doi:10.1007/s12155-012-9263-6

Abstract

Several fungal pathogens have been identified on ornamental and native stands of switchgrass (Panicum virgatum L.). Diseases of switchgrass, particularly rust, have been largely neglected and are likely to become the major limiting factor to biomass yield and quality, especially when monocultured over a large acreage. Based on teliospore morphology and internal transcribed spacer-based diagnostic primers, the rust pathogen collected from switchgrass research fields in Oklahoma was identified as Puccinia emaculata. Furthermore, to identify genetically diverse source(s) of rust resistance, several switchgrass genotypes from both upland (cv. ‘Summer’ and ‘Cave-in-Rock’) and lowland (cv. ‘Alamo’ and ‘Kanlow’) ecotypes were evaluated in Ardmore, Oklahoma during 2008 and 2009 and in growth chamber assays. Field and growth chamber evaluations revealed a high degree of genetic variation within and among switchgrass cultivars. In general, Alamo and Kanlow showed moderate resistance to P. emaculata, while Summer was highly susceptible. Distinct ecotypic variations for reactions to rust were also prevalent with the lowlands maintaining a high level of resistance. These results suggest the potential for improvement of rust resistance via the selection of resistant individuals from currently available cultivars. Further, the selection pressure on the pathogen would also be reduced by employing several rust resistant cultivars in production-scale situations.

Highlights

Switchgrass (Panicum virgatum L.) has been identified as a dedicated herbaceous bioenergy crop for cellulosic biofuel production [1,2,3]
Res. (2013) 6:458–468 encountered the scarcity of references on bioenergy crop diseases, accentuated the threats disease may pose on the economics of bioenergy crops production, and suggested the development of resistant cultivars and application of integrated agronomic management strategy to control diseases
This present study conducted in Oklahoma, one of the major states earmarked for cellulosic bioenergy production, was severely impacted by switchgrass rust in the past 5 years

Summary

Introduction

Switchgrass (Panicum virgatum L.) has been identified as a dedicated herbaceous bioenergy crop for cellulosic biofuel production [1,2,3]. High incidence of P. emaculata infection was reported in year 2000 and 2001 in cultivated or research fields in Iowa and North Dakota [12, 13] and more recently in Arkansas and Tennessee [18, 19] This present study conducted in Oklahoma, one of the major states earmarked for cellulosic bioenergy production, was severely impacted by switchgrass rust in the past 5 years. Breeding efforts are required to develop synthetic cultivars for regional deployment with increased biomass and rust resistance It is not clear if new virulent strains have emerged with increased plantings of switchgrass in experimental and large-scale pilot plantations in southern states of USA since the studies conducted by Gustafson et al [13] in South Dakota. The objectives of this investigation were to identify the pathogen of importance, develop diagnostic markers, and evaluate the variability in switchgrass cultivars including the commercially important lowland cultivars, Alamo and Kanlow, and two upland cultivars (Cave-in-Rock and Summer) that were evaluated earlier by Gustafson et al [13] in a different location

Materials and Methods

Results and Discussion

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