Abstract
We confirmed that Phytophthora rot was involved in frequent growth failure after replanting in asparagus production areas in Ehime Prefecture, Japan. According to microscopic observation, under moist conditions, zoosporangia and a septate mycelium showing the typical characteristics of Phytophthora rot formed on the lesions of stems. The isolates from the replanting soil were identified as Phytophthora nicotianae van Breda de Haan (1896) on the basis of the morphological characteristics of the zoosporangia, oogonia, oospores, and antheridia on culture media, compared with the previous reports. Also, asparagus seedlings inoculated with the isolates showed symptom in the field. In a bioassay with asparagus seedlings, the soil in which asparagus death occurred was tested, and the frequency of dead plants in non-sterilized soil was observed. In contrast, the occurrence of dead plants was completely suppressed in sterilized soil (autoclaved for 2 hours at 121℃) or fungicide-treated soil (2.0% of metalaxyl granules). Furthermore, PCR-DGGE confirmed that the density of P. nicotianae mycelia in the rhizosphere of asparagus seedlings increased from three days after transplanting.
