Pythium rot of figmarigold (Lampranthus spectabile) caused by Pythium aphanidermatum

Abstract

A new leaf rot disease was found on the leaves of figmarigold (Lampranthus spectabile). The causal organism, identified as Pythium aphanidermatum was found to cause the same symptoms after artificial inoculation and was then reisolated from the inoculated plants. We propose to name the disease Pythium rot of figmarigold. Keywords Figmarigold Á Pythium aphanidermatumFigmarigold (Lampranthus spectabile) is a popular ornamental plant with thick, fleshy leaves and brilliant flowers. Frequently, it is planted as a groundcover at the edge of gardens, crop fields and roads. In June 2004, a leaf rot disease was observed on figmarigold grown as an edging plant at the border of vegetable fields in Izunokuni City, Shizuoka Prefecture. The disease occurred mostly during the rainy season at high temperature and humidity. The disease was characterized by the conspicuous water-soaked appearance of the infected leaves, and soft rot and rapid collapse of the fleshy tissues followed (Fig. 1a-c). These leaves finally dried out to look like thin whitish, paper. Aerial mycelia were sometimes visible on the surface of lesions (Fig. 1c). With a light microscope, aseptate hyphae in the water-soaked lesions and oospores in old lesions were observed (Fig. 1d).Leaf lesions were cut into about 5 mm long pieces, surface-sterilized with 70% ethanol and 1% sodium hypochlorite solution, washed three times in sterilized water, air-dried on sterilized filter paper, and placed on 1.5% water agar (WA) plate. Hyphae grew on the plate, forming white colonies with loose, aerial mycelia. A pure culture was obtained by single-hypha isolation and maintained on potato-dextrose agar (PDA) slant.For morphological characterization of the organism, isolate Mp-1 was used to inoculate a leaf piece of figmarigold that had been autoclaved at 121°C for 15 min and placed on WA. The plate was incubated at 25°C. After 2 days, aseptate mycelia grew on WA, and sporangia consisting of swollen hyphae formed. Vesicles were formed from the sporangia, which produced zoospores 3 days after inoculation. A large number of oogonia and antheridia also formed. The presence of sterilized leaf tissue on WA was requisite to induce this morphology in isolate Mp-1.The main hyphae were 6.4-10.0 lm (ave. 7.7 lm) wide. Sporangia consisted of complexes of swollen hyphal branches. Encysted zoospores were 9.6-14.0 lm (ave. 11.3 lm) in diameter. Oogonia were terminal, globose, smooth and 22.5-29.7 lm (ave. 26.1 lm) in diameter. Antheridia were mostly intercalary or terminal, one per oogonium, monoclinous or declinous, sac-shaped, 9.5-17.8 lm (ave. 13.0 lm) long and 9.5-14.2 lm (ave. 11.2 lm) in diameter. Oospores were globose, aplerotic, one per oogonium, and 17.8-23.7 lm (ave. 20.8 lm) in diameter. The thickness of oospore wall ranged from 1.3-2.0 lm (ave. 1.7 lm) wide. Cardinal temperatures for hyphal growth on PDA were 10°C minimum, 35°C optimum and 40°C maximum, respectively. The daily growth rate at 25°C was 31.9 mm.The morphological measurements and growth response to temperature of is...

Pythium aphanidermatum Causing Pythium Rot on Lampranthus spectabilis in Korea

“…Pythium rot of trailing ice plants caused by P. aphanidermatum was previously reported in Japan (Kawarazaki et al. ) and Italy (Garibaldi et al. ).…”

“…Pythium rot of trailing ice plants caused by P. aphanidermatum was previously reported in Japan (Kawarazaki et al 2008) and Italy (Garibaldi et al 2009). To our knowledge, this is the first report of P. aphanidermatum on trailing ice plants in Korea.…”