Characterization and typing of aflatoxin-producing fungi in sugarcane fields of the southernmost Japan by cytochrome b gene analysis

Abstract

Distribution of Aspergillus flavus and A. parasiticus in sugarcane field soils, air and harvested sugarcane stems was studied in Okinawa Prefecture, the southernmost in Japan. Using a combination of dilution plate and plant debris plate techniques, the fungi were detected on all seven islands tested and in 74% of 53 soil samples. The fungi were also found on the cut surface of sugarcane stems from one of the islands. A. parasiticus was the predominant fungus although many atypical isolates of this fungus that produced metulated conidial heads were also detected. The aflatoxin producing strains were approximately 89% (146/164) of all the isolates and approximately 69% of A. flavus isolates. More than 40% of A, flavus isolates also produced G aflatoxin. SEM observation of conidial wall texture was useful for distinguishing A. parasiticus from A. flavus. Cyclopiazonic acid, an indole mycotoxin, was never synthesized by any of the A. parasiticus or G aflatoxin-producing A. flavus isolates tested. The digest this study is as follows: (1) A. parasiticus was isolated from sugarcane field soils, air and harvested sugarcane; (2) all strains of A. parasiticus isolated in these areas were different from type strain of A. parasiticus in terms of cytochrome b gene sequence and divided into 3 DNA types; and (3) the strains of afratoxin G-producing A. flavus were all A. nomius and divided into 2 DNA types. Molecular analysis of isolates showed that the strains isolated from sugarcane field soil, air and harvested sugarcane stems from the southernmost part of Japan are highly diverse and differ in terms of aflatoxin-producing ability.