LAUSR

Alternanthera philoxeroides (Mart.) Griseb is a highly invasive weed commonly found in rice fields in China. In May 2021, leaf yellowing was observed on this weed (about 10 ha) in Zhanjiang (21°19'N, 110°20'E), Guangdong Province, China. Disease incidence was approximately 20% (n = 100 investigated plants). Ten yellow leaves from 10 plants were sampled, surface-sterilized with 75% ethanol for 30 s, followed by 2% NaClO for 5 min. The leaves were rinsed three times in sterile distilled water and four sections of each leaf were placed onto potato dextrose agar (PDA). Pure cultures were obtained by transferring hyphal tips to new PDA plates. Twenty-two isolates of Fusarium ssp. (69% of the isolates) were obtained from 55% of the leaf samples. Three representative single-spore isolates (APF-1, APF-2, and APF-3) were used for further study. Colonies were white to pink on PDA. Conidiogenous cells were monophialidic or polyphialidic. Macroconidia were slightly curved, tapering apically with three to five septa, and measured from 32.5-55.8 μm × 2.5-5.1 μm in size (n=50). The morphological features of these fungi were noted to be in line with those of Fusarium proliferatum (Leslie and Summerell, 2006). For molecular identification, a colony PCR method (Lu et al. 2012) was used to amplify the internal transcribed spacer (ITS) and portions of elongation factor 1-α (EF1-α), RNA polymerase II largest subunit (RPB1), and RNA polymerase II second largest subunit (RPB2) genes using primers ITS1/ITS4, EF1-728F/EF1-986R, RPB1-R8/RPB1-F5, and RPB2-7CF/fRPB2-11aR, respectively (O'Donnell et al. 1998; O'Donnell et al. 2010). The sequences were submitted to GenBank under accession numbers MZ026797-MZ026799 (ITS) and MZ032209-MZ032217 (RPB1, RPB2, EF1-α). The sequences of the three isolates were 100% identical (ITS, 537/537 bp; RPB1, 1606/1606 bp; RPB2, 770/770 bp and EF1-α, 683/683 bp) with those of F. proliferatum (accession nos. MT378328, MN193921, MH582196, and MH582344) through BLAST analysis. Analysis of the sequences revealed a 99.87 - 100% identity with the isolates of the F. proliferatum (F. fujikuroi species complex, Asian clade) by polyphasic identification using the FUSARIUM-ID database (Yilmaz et al. 2021). The sequences were also concatenated for phylogenetic analysis by the maximum likelihood method. The isolates clustered with F. proliferatum. Pathogenicity was tested through in vivo experiments. The inoculated and control plants (n = 5, 30 days old) were sprayed with a spore suspension (1 × 105 per mL) of the three isolates individually and sterile distilled water, respectively, until run-off (Feng and Li. 2019). The test was performed three times. The plants were grown in pots in a greenhouse at 25 °C to 28 °C, with relative humidity of approximately 80%. Yellowing was observed on the inoculated plants after 7 days, while the control plants remained healthy. The pathogen re-isolated from all the inoculated plants was identical to the inoculated isolates in terms of morphology and ITS sequences. No fungi were isolated from the control plants. To the best of our knowledge, this study is the first to report F. proliferatum causing yellow symptoms on A. philoxeroides. The fungus has some potential biological control properties, but its host range needs to be further determined.