White rust outbreaks on chrysanthemum caused by Puccinia horiana in Turkey

Mehmet Erhan Göre^*

Turkish Ministry of Agriculture and Rural Affairs, General Directorate of Agricultural Research, Plant Protection Research Institute, Genclik Cad. No: 6 Bornova 35040, Izmir, Turkey

^*erhangore@bzmae.gov.tr

Accepted for publication 03/09/07

Chrysanthemum white rust is a destructive disease of many chrysanthemum (Dendranthema X grandiflorum) and related species (Dickens, 1990). The infection is caused by a fungus called Puccinia horiana Henn. This pathogen is an EPPO A2 quarantine pest, and a significant quarantine pest that is not known in Turkey.

Figure 1: Symptoms of Puccinia horiana on leaves of Chrysanthemum	Figure 2: Teliospores of Puccinia horiana

Chrysanthemum cut flowers are only grown in Izmir province of Turkey. In 2006, the area under chrysanthemum production was about 5 ha. The major areas where it is grown commercially are Seferihisar, Narlıdere, Torbalı and Urla counties. During February and March of 2007, a devastating outbreak of white rust disease severely damaged the chrysanthemum crop in 12 different glasshouses, resulting in yield losses of 80%. Disease symptoms were observed on various parts of the plant, particularly in the leaves (Fig. 1). The symptoms began as pale green to yellow spots up to 5 mm in diameter on the upper surface of infected leaves. Eventually the spots turned brown and became necrotic. Spore-forming pustules were observed on the lower surface of the leaves and were buff to pink colour. As these pustules matured, they became white in colour. Microscopic examination of the pustules revealed the presence of teliospores on pedicels up to 52 µm long; pale-yellow, oblong to oblong-clavate, slightly constricted , 30-52 x 11-18 µm, with thin walls, 1-2 µm thick, and thicker at the apex, 4-9 µm (Fig. 2). Based on these morphological characteristics, the fungus was identified as P. horiana, as described by Kapooria & Zadocks (1973).

Pathogenicity tests were conducted on 3-month-old chrysanthemum plants, by spraying unwounded leaves with a suspension of basidiospores (approximately 5 x 10⁴ per ml). Control plants were sprayed with sterile water. Inoculated and control plants were enclosed in transparent plastic bags and incubated at 20±1°C for 4 days with a 16-h photoperiod. The bag was then removed. Two weeks after spraying leaf lesions developed on inoculated plants. No disease symptoms were observed on control plants. This is believed to be the first record and outbreak of white rust disease caused by P. horiana on chrysanthemum cultivars grown in Turkey.

References

Dickens JSW, 1990. Studies on the chemical control of chrysanthemum white rust caused by Puccinia horiana. Plant Pathology 39, 434-442.

Kapooria RG, Zadoks JC, 1973. Morphology and cytology of the promycelium and the basidiospore of Puccinia horiana. Netherlands Journal of Plant Pathology 79, 236–242.