FIRST REPORT OF ROT DISEASE ON POST-HARVEST LOTUS ROOTS CAUSED BY FUSARIUM OXYSPORUM IN CHINA

Abstract

Lotus root (Nelumbo nucifera) is an economically important aquatic vegetable in China. In September 2015, rot lotus roots occurred in several storage and warehouses in Wuhan, Hubei Province, China. Samples of symptomatic epidermis were surface disinfected in 75% ethanol for 30 s, 3% sodium hypochlorite for 5 min, rinsed in sterile water for three times, dried under aseptic conditions, placed onto potato dextrose agar (PDA) and synthetic low nutrient agar (SNA) (Zhang, 2005), then kept at 26°C for 5 days in the dark. A Fusarium sp. was isolated from symptomatic and rotten epidermis. On PDA, aerial mycelia were dense and flocculent, and formed a white colony with circular, light pink to purple pigments in the medium or middle? with age. On SNA, macroconidia with 2 to 4 septa were slight, slender, curved to lunate. Microconidia were abundant and oval in shape with 0 to 1 septa. DNA was extracted by CTAB method (Borges, 2009) and the internal transcribed spacer (ITS) region comprising ITS1, ITS2 and 5.8S rDNA was amplified by primers ITS1 and ITS4 and sequenced. BLAST analysis revealed 99% similarity with F. oxysporum sequence (GenBank accession No. KX810323). Using species-specific PCR primers FOF1 (5'-ACATACCACTTGTTGCCTCG -3') and FOR1 (5'-CGCCAATCAATTTGAGGAACG-3') of F.oxysporum, a 340 bp band was obtained (Mishra et al., 2003). Pathogenicity test was performed by inoculating surface-sterilized, mature lotus roots wounded with a nail, with a mycelial plug of a 5 day-old fungus culture; lotus roots treated with plain PDA plugs were used as control. Lotus roots were placed in crispers at 18±2℃ and 75±5% relative humidity. After 3 weeks, the inoculated roots exhibited surface rot similar to that observed before. F. oxysporum was re-isolated from all inoculated lotus roots, whereas controls showed no symptoms. To our knowledge, this is the first report of F. oxysporum causing rot on post-harvest lotus roots in China.