New insight into the species diversity and life cycles of rust fungi (Pucciniales) affecting bioenergy switchgrass (Panicum virgatum) in the Eastern and Central United States

• Published in: Mycological progress Vol. 17; no. 11; pp. 1251 - 1267
• Main Authors: Kenaley, Shawn C., Quan, Menchus, Aime, M. Catherine, Bergstrom, Gary C.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-11-2018
• Subjects: Biomedical and Life Sciences; Ecology; Life Sciences; Microbiology; Original Article; Plant Sciences; Perennial grass; Phylogeny
• ISSN: 1617-416X; 1861-8952
• DOI: 10.1007/s11557-018-1434-1

Research was undertaken to clarify the taxonomic identity of leaf rust (Pucciniales) fungi on bioenergy switchgrass in the Eastern and Central U.S. We integrated internal transcribed spacer 2 (ITS2) and partial 28S ribosomal RNA gene sequence data from collections taken from cultivated switchgrass and herbarium specimens, including purported aecial and telial states of
Puccinia graminicola
and
Puccinia pammelii
. Maximum likelihood and Bayesian analyses revealed four monophyletic clades:
Puccinia emaculata
sensu stricto (s.s.),
P. pammelii
,
P. graminicola
, and
Puccinia novopanici
. Results also indicated that
P. emaculata
s.s. was not affecting cultivated, bioenergy switchgrass.
Aecidium pammelii
and
P. pammelii
were distinct phylogenetically from
P. emaculata
s.s. and grouped within a well-supported clade, demonstrating aecial-telial host alternation for
P. pammelii
between
Euphorbia corollata
and switchgrass.
Aecidium stillingiae
on queen’s delight (
Stillingia sylvatica
)—a purported aecial state host for
P. graminicola
—shared identical sequences with the recently described species
Puccinia pascua
. The latter fungus, however, was recovered within a subclade of
P. graminicola
. Hence, queen’s delight likely is not an aecial host to
P. graminicola
s.s. Additional molecular studies are warranted to determine species boundaries within the
P. graminicola
complex. The majority of contemporary collections from cultivated switchgrass were recognized as
P. novopanici
. Collectively, bioenergy switchgrass is host to at least three phylogenetically distinct species, presenting a significant challenge to the future selection and breeding of switchgrass with improved rust resistance.