FIRST REPORT OF PHAKOPSORA PACHYRHIZI TELIA IN THE UNITED STATES

Authors: HARMON, C - 5012-00-00; HARMON, P - 5012-00-00; MUELLER, T - 5012-00-00; MAROIS, J - 5012-00-00; Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2006
Publication Date: 3/1/2006
Citation: Harmon, P.F., Harmon, C.L., Mueller, T.A., Marois, J.J., Hartman, G.L. 2006. First report of Phakopsora pachyrhizi telia in the United States. Plant Disease. 90:380.

Interpretive Summary: Soybean rust, caused by Phakopsora pachyrhizi, was first reported in the continental US in 2004. In 2005, (10 Nov), the disease was confirmed in eight southern states (FL, GA, AL, MS, SC, NC, LA, and TX). Diagnoses have been based on morphological observations of asexual fruiting structure and spores of the pathogen followed by molecular confirmation. On 10 Nov 2005, both asexual and initial sexual stages were identified on leaves of kudzu (Pueraria lobata) in central Florida. This is the first report of the pre-sexual stage of P. pachyrhizi in the United States. This will be of interest to mycologist and plant pathologist working on rust fungi and soybean pathology.

Technical Abstract: Soybean rust, caused by Phakopsora pachyrhizi, was first reported in the continental US in 2004. In 2005, (10 Nov), the disease was confirmed in eight southern states (FL, GA, AL, MS, SC, NC, LA, and TX). Diagnoses have been based on visual observation of uredinia and urediniospores of the pathogen followed by PCR confirmation. On 10 Nov 2005, both uredinia and telia were identified on leaves of kudzu (Pueraria lobata) in central Florida. Telia first were noted as dark brown to black flecks on the abaxial leaf surface intermingled with abundant tan to light brown uredinia. Out of 200 leaflets counted, 143 (72%) had telia. The number of telia ranged from a few scattered telia per leaflet (1 per sq cm) to many (73 per sq cm). Telia were approximately the same diameter as uredinia but were appressed to the leaf surface and pigmented. Twenty telia were excised from host tissue under the dissecting microscope with a 20 gauge hypodermic needle. Telia averaged 89 microns by 100 microns (n=20). Four telia were crushed and five teliospores from each averaged 4.3 micron by 8.3 micron (n=20). Observations matched descriptions by Ono et al(1). This is the first report of the telial stage of P. pachyrhizi in the United States.