First report of rust caused by Pucciniastrum boehmeriae on MāMaki (Pipturus albidus) in Hawaii.
Pipturus albidus or māmaki is a flowering plant species in the Urticaceae (nettles) endemic to the Hawaiian Islands. Māmaki is a forest and agricultural commodity, as well as a traditional medicinal and fibre crop. In August 2013, leaf rust was observed in Kuristown, Hawaii (USA), on 15 māmaki 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, pulverulent, subepidermal, and dome-shaped with a central pore, consistent with Pucciniastrum. Urediniospores were 16 to 23 × 10 to 14 µm, echinulate, ellipsoid to pyriform, walls hyaline, 0.5 µm thick, contents pale yellow to bright yellow. No teliospores were observed. Based on host family, morphological characteristics, sequence analysis of the rDNA internal transcribed spacer region and pathogenicity tests, the causal agent was identified as Pucciniastrum boehmeriae. This is thought to be the first report of Pucciniastrum boehmeriae on māmaki and the first report in Hawaii on any host.