A nature farming system is an ecological farming practice that entails cultivating crops without using chemical fertilizers and pesticides. To understand the diversity and functions of root microbiomes associated with nature farming systems, we compared the root microbial community of rice under nature farming conditions with those under conventional farming conditions. High-throughput amplicon analysis demonstrated a higher abundance and greater diversity of the root microbiome under unfertilized nature farming conditions than under conventional conditions. The application of chemical fertilizers reduced the microbial diversity and abundance of some beneficial taxa important for plant growth and health. Subsequently, we isolated and identified 46 endo- and epiphytic bacteria from rice roots grown under nature farming conditions and examined their plant growth-promoting activity. Six potential isolates were selected for plant growth assessment in insoluble P- and K-containing media. Most of the isolates promoted rice growth, and Pseudomonas koreensis AEPR1 was able to enhance rice growth significantly in both insoluble P- and K-containing media. Our data indicated that nature farming systems create a distinct root microbiome that is comparatively more diverse and supports plant growth under low-input cultivation practices than under conventional practices. The potential isolates could be exploited as sources with potential applications in sustainable agriculture.

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...