First report of seedling blight of maize caused by Fusarium asiaticum in Northeast China.

Maize [Zea mays L.] is an important food and feed crops in northeast of China. In 2019, maize seedling blight with an incidence of up to 25% was found at the field in Fushun city of Liaoning Province. Typical symptoms of seedlings were yellow, thin, wilt and die. The leaves gradually became yellow from the base of the plant to the top. Root system was poorly developed. The primary roots were usually discolored and rotted. And faintly pink or puce-coloured mould was found on seeds of the rotted seedings. Symptomatic roots of diseased seedling were collected and surface-disinfested with 70% ethanol for 1 min and then in 2% NaClO for 3 min, rinsed with sterilized water three times, cut into small pieces and placed on potato dextrose agar (PDA) medium for 5 days at 25 °C. Colonies on PDA were pink to dark red with fluffy aerial mycelium and red to aubergine pigmentation with the age. The causal agent was transferred to carnation leaf agar (CLA) medium and incubated at 25°C under a 12-h light-dark cycle. 12 Pure cultures were obtained from single conidia with an inoculation needle under stereomicroscope. The harvested macroconidia were hyaline, falcate with single foot cells, 3-5 septate and 28.2- 43.5 μm × 3.7 - 4.9 μm. Chlamydospores were globose to subglobose (5 to 13.5 μm). No microconidia were found. The perithecia were black, ostiolate subglobose. Asci were hyaline, clavate, measuring 58.1- 83.9 µm × 7.7- 11.9 µm and contained eight ascospores. Morphological characters of the pathogen agreed well with descriptions of Fusarium asiaticum (O'Donnell et al.2004; Leslie and Summerell 2006). To confirm the identity, partial translation elongation factor 1 alpha (TEF1-a) gene and rDNA internal transcribed spacer (ITS) region of isolate MSBL-4 were amplified and sequenced (O'Donnell et al. 2015; White et al.1990). BLASTn analysis of both TEF sequence (MT330257) and ITS sequence (MT322117), revealed 100% sequence identity with F. asiaticum KT380116 and KX527878, respectively. The isolate MSBL-4 was NIV chemotype as determined by Tri13F/DON, Tri13NIV/R (Chandler et al, 2003) assays. Pathogenicity studies were conducted on maize hybrid "Liaodan 565". Inoculum of F. asiaticum was prepared from the culture of MSBL-4 incubate in 2% mung beans juice on a shaker (150 rpm) at 25°C for 48 hours. The five liter pots (10 pots) were filled with sterilized field soil and five of them were mixed with conidial suspension (300mL in each pot) at 2 × 105 conidia per ml. Ten kernels per pot were surface disinfected in 2% sodium hypochlorite for 5 min, rinsed with sterilized water and planted. Five pots were inoculated and another uninoculated five pots served as controls. The pots were maintained in a greenhouse at 22-26°C for 40 days. Leaves of the plants in inoculated pots were yellowing and the roots became discolored or necrotic rot at 4 weeks after seedling emergence. All characteristics of the disease were similar to those observed in field. Non-inoculated control plants had no symptoms. Fusarium asiaticum was reisolated from inoculated plants and was identical to the original isolate. The experiment was repeated once with similar results. To our knowledge, this is the first report of seedling blight caused by F. asiaticum on maize in northeast China, and it has posed a threat to maize production of China. References: Leslie J F and Summerell BA. 2006. The Fusarium laboratory manual. Blackwell Publishing, Ames, pp 176-179. O'Donnell et al.2004. Fungal Genetics and Biology 41: 600-623. O' Donnell et al. 2015. Phytoparasitica 43:583-595. White T J et al. 1990. Academic Press, San Diego, CA, pp 315-322. Chandler E A et al. 2003. Physiological and Molecular Plant Pathology 62(6): 355-367.