Phytophthora citrophthoraによるショウガ疫病（新称）

Abstract

In 1997, Phytophthora rot caused serious losses to ginger (Zingiber officinale Rosc.) production in Kochi Prefecture, Japan. In the field in early summer and autumn, water-soaked rot on basal pseudostems and brown rot on rhizomes were first observed, then plants developed stem blight. The disease also developed on rhizomes stored at 15°C in the dark. A Phytophthora sp. was consistently isolated from the symptomatic lesions and caused the same symptoms after inoculation with the isolates. The identical Phytophthora sp. was then reisolated. White stellate colonies grew on PDA at a minimum temperature of 10°C, optimum of 23°C and maximum of 30°C. Sporangia were ovoid, ellipsoid, globose and distorted (variable) with one or two apices, noncaducous, 30–90 × 20–50 (average 50.0–56.1 × 25.0–32.6) μm, with a length to breadth ratio of 1.5–1.7:1. Nucleotide sequence of the r-DNA ITS regions agreed well with those of Phytophthora citrophthora (R. E. Smith and E. H. Smith) Leonian previously reported. Based on these results, the isolate was identified as P. citrophthora. This report is the first of a disease of ginger caused by P. citrophthora, and we propose the name “Phytophthora rot” for the disease.