Occurrence of Fusarium boothii Causing Fusarium Head Blight and Crown Rot of Wheat in China

In 2023, a survey of Fusarium head blight (FHB) and Fusarium crown rot (FCR) was undertaken in the Huanghuai wheat growing region, China (Zhang et al. 2024). The 10 symptomatic whole wheat plants were obtained from a commercial field in Suzhou City (33.639811 °N, 117.089560 °E), Anhui province. Fusarium-like colonies were consistently isolated from symptomatic wheat spikelets (9 strains) and basal stem (1 strain), resulting in 10 monoconidial strains as previously described (Zhang et al. 2024). The morphology (colony, pigment, and macroconidia shape) of these ten strains was consistent with the description of the Fusarium graminearum species complex (Leslie and Summerell 2006). Their colonies grow rapidly and produce dense aerial mycelia that vary from white to orange in color, with pink pigment at the bottom. Macroconidia were gradually curved with prominent foot-shaped basal cells, primarily three to five septa. Microconidia were absent. To identify the strains to accurate species, portions of the translation elongation factor 1α (TEF) gene were amplified using primer pair EF1/EF2 (O’Donnell et al. 1998) and bidirectionally sequenced. The obtained sequences were assembled and subjected to pairwise DNA alignments against reference databases Fusarioid-ID (https://www.fusarium.org/) and MycoBank (https://www.mycobank.org/). BLASTn queries on the ten TEF fragments revealed that five strains were identified as F. asiaticum based on similarity to the reference sequences of F. asiaticum strain LC7501 (accession no. MW620102) ranging from 99.69 to 100%, and three strains were identified as F. graminearum due to 100% homology with F. graminearum strain LC13775 (accession no. MW620072). The TEF sequences of strains AH-3 (accession no. PQ683742) and AH-9 (accession no. PQ682662) exhibited the highest similarities, 100% and 99.85%, respectively, to F. boothii strain CBS316.73 (accession no. GQ915503). Furthermore, identical ITS (ribosomal DNA internal transcribed spacer) sequences were amplified from strains AH-3 and AH-9 (accession no. PQ772045) using primer pair ITS1/ITS4 (White et al. 1990), resulting in 100% homology with F. boothii strain CBS316.73 in MycoBank. F. boothii has been already reported as the cause of maize stalk rot in Yunnan, China (Xi et al. 2021). To the best our knowledge, however, this is the first report of F. boothii causing FHB and FCR on wheat in Anhui, as well as in China. Conidial spore suspension (5 × 105 spores/mL) of strains AH-3 and AH-9 were generated in a half-strength CMC broth (carboxymethyl cellulose) as described (Wang et al. 2014) and their pathogenicity had been verified following Koch’s postulates. Fifteen wheat heads (cultivar Zhengmai 1860) were individually inoculated at anthesis with 10 µL spore suspension of strain AH-3 by single floret injection in the field in April 2024, as previously described (Wang et al. 2014). The pathogenicity of strain AH-9 was tested by wheat coleoptiles inoculating (cultivar Zhengmai 1860, ten duplicates) and then maintained in a humid growth chamber (25 °C, 12-h photoperiod) (Zhang et al. 2015). Wheat plants (heads or coleoptiles) inoculated with sterilized water served as control groups. Typical FHB and FCR symptoms developed individually in inoculated plants 14 days post inoculation, whereas the control plants were symptomless. F. boothii strains were reisolated from the symptomatic plants but not from the controls. Collectively, these results support the conclusion that, F. boothii was one of the causes of FHB and FCR in China even with low frequency.