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Title: First report of Gymnosporangium yamadae, Japanese apple rust, on Malus from North America

item Rossman, Amy

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2009
Publication Date: 3/9/2009
Citation: Yun, H., Minnis, A., Rossman, A.Y. 2009. First report of Gymnosporangium yamadae, Japanese apple rust, on Malus from North America. Plant Disease. 93:430.

Interpretive Summary: Rust fungi are a very large and diverse group of parasites that attack crop and forest plants. Accurate knowledge of the distribution of rusts is important for tracking the movement of these disease-causing fungi. In this research a rust fungus that infects apples and other plants in the same genus was discovered for the first time in the North America. The rust was observed on leaves of crab apple in Delaware and Pennsylvania. Until now, this rust species was known only from Asia. Knowledge of the distribution of plant pathogenic fungi is useful to agronomists and plant pathologists as well as plant regulatory and quarantine officials.

Technical Abstract: Plants in the genus Malus Mill. are used in temperate regions for fruit crops such as apple and as ornamental landscape plants. Gymnosporangium yamadae Miyabe ex G. Yamada, cause of Japanese apple rust, is known to attack several economically important species of Malus in Asia. In August 2004 and July 2008, the aecial stage of a rust fungus was observed in Delaware and Pennsylvania on leaves of crab apple (Malus toringo (Siebold) Siebold ex de Vriese, often referred to as its synonym Malus sieboldii (Regel) Rehder). This fungus was identified as G. yamadae. This is the first report of this rust pathogen in North America. The identification was confirmed by morphological comparisons with Asian material and descriptions (1, 2) as well as using 28S rDNA sequence data from Asian material. The aecia of G. yamadae are foliicolous, hypophyllous, roestelioid, 4–7 mm high. The peridia are cornute to tubular, at maturity typically becoming lacerate but not at the apex; peridial remains often form a reticulated pattern while retaining the cornute to tubular shape. The peridial cells are long-narrow rhomboid, 83–120 µm long with smooth outer walls and verrucose to echinulate inner and side walls. The aeciospores are more or less globose, 18–28 × 19–29 µm, with a slightly coronate surface and walls brown yellow, 2–3 µm thick. The telia on Juniperus were not observed. The specimens were deposited in the U.S. National Fungus Collections (BPI 878846, BPI 878847, BPI 878848 and BPI 878849). The 28S rDNA sequence of G. yamadae from BPI 878849 was deposited in GenBank as FJ455091.