FIRST REPORT OF BROWN PATCH OF POLYGONATUM ODORATUM CAUSED BY FUSARIUM OXYSPORUM IN CHINA

Abstract

Polygonatum odoratum (Mill) Druce is a herb used in China for treating diabetes mellitus and cardiovascular diseases. In June 2007, extensive attacks of a disease (brown patch) were observed in a P. odoratum field in Qingyuan (China). Brown streaks, first appearing on the abaxial leaf surface, soon extended to the adaxial surface and enlarged to dark brown patches. Isolations made from small pieces of leaf tissues plated on potato dextrose agar yielded white to pale-violet fungal colonies, producing macroand microconidia. The macroconidia were thin-walled, 3-septate and measured 30-50×3-5 μm, whereas microconidia were 0-septate, elliptical, and were formed abundantly in false heads. The 5.8S subunit and flanking internal transcribed spacers (ITS1 and ITS2) of the rDNA gene were amplified from DNA extracted from single-spore cultures using the ITS1/ITS4 primers (White et al., 1990) and sequenced. The ITS sequence was 99% similar to that of Fusarium oxysporum (accession No. EU520062), thus supporting, along with the observed morphological traits, the identification of the causal fungus as F. oxysporum (Leslie and Summerell, 2006). For pathogenicity tests (conducted twice) a conidial suspension of 1×105 spores/ml was sprayed on ten 5-week-old plants, which were then covered with polythene bags and kept for 48 h at 26±1°C. Control plants were sprayed with sterile water. Typical symptoms developed on all inoculated plants after 15 days, and F. oxysporum was consistently re-isolated from symptomatic tissues and identified as previously described. Control plants remained symptomless. To our knowledge, this is the first report of F. oxysporum causing brown patch on P. odoratum in China.