Fusarium spp. Associated with Rice Bakanae Disease in Zhejiang, China

Rice bakanae disease (RBD) occurs at all growth stages of rice, leading to yield loss and rice seed contamination. We sampled plants with bakanae symptoms and aerial adventitious roots from early-season rice fields, and obtained a total of 152 Fusarium isolates. Based on a combination of sequences from a region of the tef1 gene and morphological features, Fusarium isolates were identified as F. fujikuroi (142 isolates, 93.4%), F. proliferatum (8 isolates, 5.3%), and F. oxysporum (2 isolates, 1.3%). We found that 30 °C was suitable for the sporulation of all three Fusarium species. However, for mycelial growth, the temperature suitable for F. oxysporum was higher than that for F. fujikuroi and F. proliferatum. On a susceptible rice, F. fujikuroi caused foolish seedlings (excessive growth rate ranging from 29.87% to 116.57%); F. proliferatum and F. oxysporum led to stunted symptoms. Quantification of gibberellic acid (GA3) by high-performance liquid chromatography (HPLC) revealed that only F. fujikuroi isolates produced large amounts of GA3, explaining why only F. fujikuroi isolates caused bakanae symptoms. The infected rice seedlings were continuously cultivated in the greenhouse. All three Fusarium species caused crown rot in rice plants. Additionally, F. fujikuroi caused root rot and grain sterility, whereas F. proliferatum and F. oxysporum caused heading failure. Collectively, our study indicated that three Fusarium species were associated with RBD in early-season rice in Zhejiang, China, and they caused distinct symptoms in rice.