Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/12/2013
Publication Date: 6/1/2014
Citation: Demers, J.E., Mckemy, J.M., Bushe, B., Kumashira, B., Ko, M., Castlebury, L.A. 2014. First report of rust caused by Pucciniastrum boehmeriae on mamaki (Pipturus albidus) in Hawaii. Plant Disease. 98(6):855. Interpretive Summary: Fungi are a large and diverse group of organisms that cause serious diseases of crop and forest plants. Knowledge of the host range and geographic distribution of disease-causing fungi is critical for managing the movement of these destructive organisms. Recently a rust fungus was found on leaves of a flowering plant in Hawaii known as mamaki used in traditional medicine and as a fiber crop. This rust was identified using both morphological and molecular characteristics and determined to be a species previously known only from Asia and South America. This rust fungus is reported for the first time from this host plant and for the first time from the United States. Using these data plant pathologists will be able to control this disease and plant quarantine officials may be able to prevent the spread of this fungus to other parts of the United States.
Technical Abstract: Pipturus albidus (Hook. & Arn.) A. Gray or mamaki is a flowering plant species in the Urticaceae (nettles) endemic to the Hawaiian Islands. Mamaki is a forest and agricultural commodity, as well as a traditional medicinal and fiber crop. In August 2013, a leaf rust was observed in Kuristown, Hawaii, on 15 mamaki plants. Infected leaves had vein-delimited chlorotic spots on the adaxial surface and yellow to orange uredinia on the abaxial surface. Uredinia were scattered, minute, subepidermal, and pulverulent.Urediniospores were 16–23 µm x 10–14 µm, echinulate, ellipsoid to pyriform, walls hyaline, 0.5 µm thick, contents pale yellow to bright yellow. No teliospores were observed. A voucher specimen was deposited in the U.S. National Fungus Collections (BPI 892695). The only species of Pucciniastrum previously known on Pipturus, Pucciniastrum pipturi Syd. (syn. Uredo pipturi (Syd.) Hirats. has larger urediniospores, 26.5–40.0 µm x 19.5–27.5 µm. The pathogen was identified as Pucciniastrum boehmeriae Syd. & P. Syd., which infects Boehmeria Jacq., also in the Urticaceae, and has urediniospores that are 18–27 µm x 13–18 µm in size and similar in shape. DNA was extracted from uredinial lesions and the nuclear ribosomal internal transcribed spacer (ITS2) region and the 5’ end of large subunit (28S) were amplified and sequenced following the protocol of Aime. The resulting fragment was 100% identical to authenticated and vouchered P. boehmeriae ITS2/28S rDNA sequences. Sequences from P. pipturi are not available for comparison, but host family, molecular and morphological data support the identification of the rust as P. boehmeriae, which is found throughout eastern Asia and South America. To our knowledge, this is the first report of P. boehmeriae on mamaki as well as the first report of P. boehmeriae in Hawaii. Plant health professionals and regulatory officials will use this information to establish survey methods and implement appropriate management practices to control this rust disease.