Draft genome assemblies for tree pathogens Phytophthora pseudosyringae and Phytophthora boehmeriae

Species of Phytophthora, plant pathogenic eukaryotic microbes, can cause disease on many tree species. Genome sequencing of species from this genus has helped to determine components of their pathogenicity arsenal. Here we sequenced genomes for two widely distributed species, P. pseudosyringae and P. boehmeriae, yielding genome assemblies of 49 Mb and 40 Mb, respectively. We identified more than 280 candidate disease promoting RXLR effector coding genes for each species, and hundreds of genes encoding candidate plant cell wall degrading carbohydrate active enzymes (CAZymes). These data boost genome sequence representation across the Phytophthora genus, and form resources for further study of Phytophthora pathogenesis.

Phytophthora boehmeriae. [Distribution map].

A new distribution map is provided for Phytophthora boehmeriae Sawada. Oomycetes: Peronosporales: Peronosporaceae. Hosts: cotton (Gossypium spp.), ramie (Boehmeria nivea), chillies (Capsicum annuum), Citrus spp. and Pinus spp. Information is given on the geographical distribution in Europe (Greece, Mainland Greece), Asia (China, Anhui, Hebei, Hainan, Jiangsu, Jiangxi, Jilin, Liaoning, Shaanxi, Shandong, Shanxi, Sichuan, Xinjiang, Zhejiang, India, Karnataka, Madhya Pradesh, Tamil Nadu, Japan, Korea Republic and Taiwan), Africa (South Africa), North America (Mexico), South America (Argentina, Brazil, Rio Grande do Sul) and Oceania (Australia, New South Wales, Queensland, Victoria, Western Australia and Papua New Guinea).

Basal Rot of Geraldton Waxplant Caused by Phytophthora boehmeriae

Geraldton waxplant (Chamaelauciun uncinatum Schauer.) is a shrub that produces flowered branches used in bouquets. Waxplant was introduced into Argentina (Buenos Aires province) in the 1990s and currently is cultivated in greenhouses. In the summer of 1995, a previously undescribed disease was observed on plants at different stages of growth. Plants showed a progressive yellowing of the branches from the base to the top of the stems. Leaves of diseased plants became grayish green, then yellow, and finally straw colored. Leaves remained attached to the branches after the plants died. Roots and stem discoloration was observed and the root cortex sloughed off. A Phytophthora sp. was isolated from the roots and lower stems of symptomatic plants. Koch's postulates were completed in a greenhouse at 28 to 34°C using the cvs. Snowflake, Violet, and Orchid. Inoculum was obtained by growing the fungus for 7 days in Petri dishes containing an autoclaved wet mixture of polished rice + wheat bran + V8 juice + perlite (1:1:1:1, by volume). The inoculum was mixed with soil (4:100, wt/wt) in pots, and 15 4-month-old plants per cultivar were transplanted into infested and noninfested soil. Plants of the cv. Snowflake were the most susceptible with symptoms starting 25 days after inoculation. At the end of the trial (five months) 86% of these plants died. Disease development was delayed on plants of cvs. Orchid and Violet and mortality was only 20% on Orchid and 26% on Violet. Control plants remained healthy. The Phytophthora sp. was reisolated from plants showing typical symptoms. The fungus was cultivated on potato-dextrose agar at 25°C and morphological characteristics were recorded. The colony diameter was 3.7 cm after 5 days. Ovoid, obturbinate and obpyriform to limoniform, papillate and caducous sporangia were observed. They averaged 42.1 ± 10.7 × 31.7 ± 9.2 μm (range 25.0 to 65.0 × 18.7 to 55.0 μm) with a length-breadth ratio = 1:1 to 1.81, av. 1.25:1. Many sporangia were distorted in their shapes and averaged 61.7 ± 30.5 × 24.8 ± 4.5 μm (range 27.5 to 125.0 × 20.0 to 32.5 μm) with a length-breadth ratio = 1.31:1 to 4.6:1, av. 2.1:1. After the zoospores were discharged, a narrow exit pore was observed (3.7 to 8.7 μm, av. 6.9 μm). Pedicels were not conspicuous or were short when present. Oogonia and amphigynous antheridia were readily observed in single culture. Spherical oospores nearly filling the oogonium and containing many subcellular inclusions averaged 29.7 ± 8.9 μm (range 17.5 to 47.5 μm). Terminal or intercalary, rounded to ovoid chlamydospores developed in smooth or swollen hyphae. Based on cultural and morphological characteristics, the species infecting waxplant was identified as P. boehmeriae Sawada (1). This is the first record of P. boehmeriae on geraldton waxplant. References: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN.