First Report of Fusarium proliferatum Causing Pinellia ternata Corm Rot in Henan, China

Pinellia ternata (Thunb.) Makino is a perennial herb of the genus Pinellia in the Araceae family, which is a kind of precious Chinese herbal medicine (Bai et al. 2022). In May 2023, rotting was observed on P. ternata corm in the Tanghe planting base (3.33 ha, 32º46´6˝N, 113º 8´47˝E, 138 m), with an incidence of approximately 10%. To identify the causal agent, five rotten corms were randomly sampled from the Tanghe planting base. Symptomatic corm tissues were cut into small pieces (3 mm3) with asymptomatic tissue margins, disinfected in 75% ethanol for 30s and in 2% sodium hypochlorite for 3 min, rinsed three times with sterile distilled water, and then placed on synthetic nutrient-poor agar (SNA) plates incubated at 20℃ with a 12 h light/dark photoperiod. Hyphal-tips from the growing edge of colonies were transferred to fresh SNA to obtain pure cultures. In total, five pure isolates were obtained with similar colony morphology and white (top view) or grayish white (back view) coloration, with villous surfaces and abundant aerial hyphae. On SNA, the isolates mainly produced microconidia. Microconidia were ellipsoidal to cylindrical, thin-walled, smooth, hyaline and measured 5.40 to 11.98 (av. 7.14) µm long and 1.60 to 5.38 (av. 2.54) µm thick (n=50). Based on these morphological characteristics of colony and conidia, the causal agent was preliminarily identified as Fusarium sp. (Crous et al. 2021). To confirm pathogen identity, the total genomic DNA of 2 isolates (BX-2 and BX-3) was extracted using the 2×T5 Direct PCR kit (Beijing Tsingke Biotech Co., Ltd, Beijing, China). The internal transcribed spacer (ITS), RNA polymerase II second largest subunit (rpb2), translation elongation factor 1-alpha (tef1), and β-tubulin (tub2) gene were PCR-amplified using the universal primers ITS1/ITS4, 5f2/7cr, EF-1/EF-2 and BT2F/BT4R (Crous et al. 2021), respectively. Sequences have been deposited in GenBank (PP125560-PP125561 for ITS, PP782474-PP782475 for rpb2, PP782476-PP782477 for tef1, PP171436-PP171437 for tub2). BLAST search showed that all sequences were 99% to 100% homology with the corresponding sequences of Fusarium proliferatum (CBS 182.32). A phylogenetic tree was constructed based on the Maximum-Likelihood method in MEGA-X (Kumar et al. 2018) and revealed that the two isolates were closest to F. proliferatum. The pathogenicity tests were conducted with the two isolates (BX-2 and BX-3) as described by Liu et al. (2022) with slight modifications. For each treatment, five healthy P. ternata corms were inoculated with 1ml of conidial suspension (1×107 conidia/ml). Control plants (n=5) were inoculated with sterilized water. All samples were covered with plastic bags and maintained at a relative humidity greater than 90% in a greenhouse at 20℃ with a 12 h light/dark photoperiod. After 15 days, inoculated corms showed similar symptoms to those on the original diseased plants, while control plants remained symptomless. F. proliferatum was successfully reisolated from the inoculated plants and identified based on its morphological characteristics. Thus, Koch's postulates were fulfilled. The experiment was repeated thrice with similar results. Morphological characteristics, sequence alignment and Koch's postulates test confirmed that F. proliferatum was the cause of P. ternata corm rot disease. To our knowledge, this is the first report of F. proliferatum causing P. ternata corm rot in Henan province, China. Our findings are important for informed surveillance of the disease.