First Report of Puccinia pelargonii-zonalis Causing Rust on Pelargonium × hortorum in Xinjiang Province, China.

Abstract

Geranium (Pelargonium × hortorum) is an ornamental plant cultivated throughout world. In May 2019, typical symptoms of rust with nearly 90% disease incidence were observed on leaves of Pel. × hortorum growing in pots in a scenic spot in the ancient city of Kashgar, Xinjiang province, China. Early symptoms of the disease appeared small lesions with pale-yellow halos on the lower leaf surfaces. Infected tissues subsequently formed a concentric circle of sori on lesion reaching a final diameter of 0.5 to 1.5 cm, which resulted in leaf blighting and premature. Two representative specimens were deposited in the Mycological Herbarium of Tarim University (HMUT 8001 and HMUT 8002). Urediniospores were globose or subglobose to ovoid, light brown, echinulate, thin-walled with two conspicuous subequatorial pores, 19.8 to 27.3 × 17.8 to 23.6 μm (24.3 × 21.7 μm average, n=30). Telia and teliospores were not seen. The sizes and characteristics of urediniospores were similar with those of Puccinia pelargonii-zonalis as described by Doidge (1926). To confirm the identification, genomic DNAs were extracted directly from sori on diseased leaves from isolates HMUT 8001 and HMUT 8002. The part of the nuclear large subunit (LSU, 28S) rDNA was amplified and sequenced following Aime et al. (2006), and deposited in GenBank (Accession Nos. MT648851 and MT648852). An NCBI blast search indicated that 99.6% identity of the LSU (772/775 nucleotides) with Puc. pelargonii-zonalis on Pel. hortorum (KX999887) from Australia (Marin-Felix et al. 2017). The phylogenetic analysis based on the LSU sequences using Maximum-Likelihood and Bayesian methods placed the Xinjiang isolates from Pel. × hortorum in the same clade with the reference sequences of Puc. pelargonii-zonalis. Pathogenicity test was confirmed by Koch's postulates. Leaves of three healthy potted plants were sprayed with a spore suspension (2 × 105 spores/ml). Sterile water was sprayed on three healthy seedlings as controls. Inoculated and control plants were covered with a plastic bag and placed in a moist chamber with 90% relative humidity at 25°C. Initial symptoms were observed with small light-yellow spots on the upper surface after 15 days, but not in the control plants. Puc. pelargonii-zonalis has been previously reported on Pel. × hortorum in Argentina, Australia, Canada, Georgia, Greece, India, Mexico, New Zealand, Norway, Portugal, South Africa, the United States, and Venezuela (Farr and Rossman 2021). Geranium rust was first found in Yunnan province in southwestern China (Zhou and Zhuang 2005). However, this is the first report of geranium rust in Xinjiang province in northwestern China. The occurrence of the disease seriously affected their ornamental and economic value.