First Report of Uromyces transversalis, Causal Agent of Gladiolus Rust, in San Diego County, California

Abstract

In May 2006, signs and symptoms of a rust disease were observed on hybrid gladiolus plants in a home garden located in the city of San Diego, CA. Uredinial lesions were bright orange, variable in shape from globose to oval to transversely elongate, and measured 28 to 652 × 36 to 994 μm. Urediniospores measured 16 to 26 × 16 to 23 μm and had hyaline walls that were 2 μm thick and finely echinulate with recurved spines. Some uredinial lesions located primarily at the base of the leaves were surrounded by dark, irregular lesions (telia) by the epidermis. Telia contained nonseptate, light-to-chestnut brown teliospores that measured 20 to 30 × 13 to 20 μm with an apical thickening measuring 2 to 5 μm. Teliospore pedicels measured 3 to 33 × 2 to 5 μm. Groups of teliospores were separated into locules by upright, pale brown paraphyses. The rust was identified as Uromyces transversalis, the cause of gladiolus rust and a quarantine pest for the United States. An intensive 23 square mile survey was initiated and resulted in the detection of infected plants at one nearby residence 200 feet away, in a commercial nursery six miles east of the initial site of detection, and at a residence across the street from the infected nursery. Plants in the nursery were grown outdoors in three blocks, in which the disease incidences were 20, 80, and 100% with varying levels of severity. Telia were also found at this location. The nursery grows gladiolus flowers for sale at local farmer markets, sometimes supplemented by additional cut gladiolus from Mexico. U. transversalis is known to occur in Mexico (2). This rust is under eradication at all four sites. Gladiolus rust was reported in Florida in April 2006. To our knowledge, this is the first confirmed report of Gladiolus rust in California. References: (1) J. R. Hernández. Invasive Fungi. Gladiolus Rust. Systemic Botany and Mycology Laboratory, Online publication. ARS, USDA, 2004. (2) G. Rodríguez-Alvarado et al. Plant Dis. 90:687, 2006.