The telial stage of Gymnosporangium exiguum (2) on Ashe juniper (Juniperus ashei) was observed in Bandera County, TX, in April and May 1999 after rain events. Symptomatic plants with multiple lesions were found at low frequencies in dense J. ashei populations. Orange telia formed on scales and bark and on 2- to 3-mm-diameter twigs and became nearly inconspicuous when dry. No hypertrophy was observed. Previously reported telial hosts include J. californica and J. excelsa cv. Stricta in California; J. mexicana and J. scopulorum in Oklahoma; J. virginiana in Texas; and J. deppeana var. pachyphloea in Oklahoma and Texas (1). An aecial stage identified as G. exiguum has been observed for many years on native hawthorns (Crataegus crus-galli, C. greggiana, C. mollis, C. stevensiana, C. tracyi, C. turnerorum, C. viridis var. desertorum, and several natural hybrids) in Bandera, Bexar, Edwards, Gillespie, Kendall, Kimble, Real, and Uvalde counties, Texas. Prominent roestelioid aecia were observed on hawthorn leaves, petioles, fruits, peduncles, thorns, and, less often, on twigs. In two experimental plantings of hawthorns in Bandera County, rust severity was rated as low to moderate in six populations of C. greggiana and hybrids; moderate in two populations each of C. stevensiana and C. tracyi; moderate to severe in three populations of C. crus-galli and hybrids; and severe in one population each of C. mollis and C. viridis var. desertorum. G. exiguum was previously reported on a Crataegus sp. in Texas and on Heteromeles arbutifolia in California (1). Flowers, fruits, plant forms, and drought tolerances are characteristics of some endemic hawthorns that provide landscape and wildlife advantages. G. exiguum causing rust disease may limit the ornamental potential of highly susceptible hawthorn species in southwest Texas. Inconspicuous infections on susceptible ornamental Juniperus spp. also could have phytosanitary implications. Voucher specimens (aecia and telia) are on deposit in the Mycological Herbarium, Department of Plant Pathology, North Carolina State University, Raleigh.
References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN. (2) F. D. Kern. 1973. A Revised Taxonomic Account of Gymnosporangium. The Pennsylvania State University Press, University Park.
