Effects of temperature and humidity on the survival of urediniospores of Gladiolus rust (Uromyces transversalis)

Authors: Peterson, Gary; Berner, Dana

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2009
Publication Date: 6/12/2009
Citation: Peterson, G.L., Berner, D.K. 2009. Effects of temperature and humidity on the survival of urediniospores of Gladiolus rust (Uromyces transversalis). European Journal of Plant Pathology. Published online (DOI 10.1007/s10658-009-9492-5).

Interpretive Summary: Gladiolus rust, caused by the fungal plant pathogen, Uromyces transversalis, is a serious concern to commercial greenhouse and nursery enterprises growing hybrid gladiolus cultivars for cut flower production and is considered to be of plant quarantine importance in Europe and the United States. In 2006, the pathogen was observed for the first time in several commercial cut flower operations in Florida, and later that year on several commercial production farms in southern California. Limited outbreaks were reported again from both states in 2007 and 2008. USDA initiated an eradication program that recommended the immediate removal and destruction of infected plants followed by a host free period, use of a fungicide treatment schedule, and equipment decontamination. In support of this plan, a study was conducted to determine how long the infecting urediniospores of U. transversalis would survive over a range of temperatures and relative humidities. Results showed that relative humidity had no significant effect on viability while temperature was a significant factor. In these studies, the fastest decline to no germination was 49 days at 25 degrees C. The most favorable temperature for sustainable germination of urediniospores was 15 degrees C where trace germination continued for 71 days. No germination was observed in any treatment at 79 or 86 days. Results support the USDA recommendation of a 90-day host free period for infested greenhouses and nurseries, and suggests that structural solarization of greenhouses could significantly reduce this time.

Technical Abstract: Uromyces transversalis is a autoecious microcyclic rust mainly infecting Gladiolus spp. The pathogen is considered of plant quarantine importance in Europe and the United States. In 2006, the pathogen was found for the first time in the United States in several commercial nurseries in Florida and California. USDA initiated an eradication program that recommended the immediate removal and destruction of infected plants followed by a host free period, use of a fungicide treatment schedule, and equipment decontamination. In support of this plan, a study was conducted to determine how long urediniospores of U. transversalis would continue to germinate at temperatures of 2.8, 15.0, 18.8 and 25.0 degrees C under controlled relative humidities of 11, 23, 43, 75, 93 and 100 percent. Analysis of variance indicated no significant effect of relative humidity on urediniospore germination but a highly significant effect of temperature. No germinating urediniospores were detected after 79 days for any treatment. The greatest germination over time was observed at 15 degrees C and was more likely the result of germination independent of any low- or high-temperature induced spore quiescence. Thus, lack of germination after 79 days was probably a good indicator of lack of germinable spores after this time for the 15 degrees C treatment.