Da. Willits et Je. Sherwood, Polymerase chain reaction detection of Ustilago hordei in leaves of susceptible and resistant barley varieties, PHYTOPATHOL, 89(3), 1999, pp. 212-217
Although Ustilago hordei infects barley seedlings, symptoms of the disease
covered smut are not visible until heading. Natural or artificial inoculati
on usually results in inconsistent infection, even in highly susceptible li
nes. Thus, breeding for resistance to covered smut is time consuming and di
fficult. The ribosomal DNA internal transcribed spacer (ITS) regions of U.
hordei were sequenced and a primer pair was developed for polymerase chain
reaction (PCR). These primers amplified a 574-bp fragment from DNA of Ustil
ago spp., but did not amplify DNA from barley or other common barley pathog
ens. DNA extracted from as few as four U. hordei sporidia was detected by t
his method. U. hordei DNA was amplified from leaf tissue of inoculated susc
eptible and resistant plants at different stages of plant development in di
fferential varieties. Growth of the fungus in different leaves of an indivi
dual plant was variable. Several highly resistant varieties were shown to c
ontain U. hordei DNA in the first three to four leaves, but not in later le
aves. Thus, although the fungus can infect many resistant plants, the plant
s remain symptomless. Detection of U. hordei prior to heading should assist
efforts far breeding for resistance and provide clues concerning the mecha
nisms of resistance employed by different resistance genes.