First Report of <i>Fusarium pseudensiforme</i> and <i>Fusarium suttoniana</i> Causing Stem Base Rot on <i>Pueraria thomsonii</i> in China

Pueraria thomsonii Benth. is a leguminous vine grown in southern China for its edible, starch-rich roots. In May 2025, typical stem base rot was observed on plants in a commercial field of approximately 0.4 hectares in Wuzhou, Guangxi (23°32'12"N, 110°39'29"E), with disease incidence about 30%. Symptoms began as yellowish-brown discoloration on basal stems, turning dark brown with longitudinal cracks, brown dry rot of underlying tissues, and reddish-brown vascular discoloration. Late-stage stems exhibited black, dry, hollow rot; severely infected plants showed reduced branching, leaf thickening, and basal leaf yellowing, leading to death. Symptomatic tissues (5 × 5 mm) from lesion margins were surface-disinfested (75% ethanol 10 s, 2% NaOCl 5 min, rinsed thrice), placed on potato dextrose agar, and incubated at 28°C in darkness. Fifteen isolates were obtained via single-spore purification. Two morphological groups were identified. Group 1 (GG-F1) produced white, floccose colonies with abundant macroconidia: fusiform, slightly curved, 5-6 septate, (45-91) × (2.8-5.5) µm (n=50), with a distinct foot cell and bent apical cell. Group 2 (GG-F2) formed creamy-white to buff colonies with abundant microconidia: hyaline, oval to reniform, aseptate or 1-septate, (5.3-12.5) × (1.6-4.1) µm (n=50); macroconidia were sparse, stout, cylindrical with blunt apex and 3-5 septa. Genomic DNA was extracted from the three isolates using the CTAB method (Sagar et al. 2014). The ITS, EF-1α, and RPB2 regions were amplified and sequenced. BLAST analysis by Fusarioid-ID database (https://www.fusarium.org/page/ID) showed that GG-F1 shared 99.76% (ITS), 99.76% (EF-1α), and 99.85% (RPB2) identity with ex-type strains of Fusarium pseudensiforme (Neocosmospora pseudensiformis, now by Fusarioid-ID database); GG-F2 shared 100%, 99.76%, and 100% identity with Fusarium suttoniana (Neocosmospora suttoniana, now by Fusarioid-ID database), respectively. A multilocus phylogenetic tree confirmed the placements. Sequences were deposited in GenBank (ITS, PZ176910 and PZ176911; EF-1α, PZ196199 and PZ196200; RPB2, PZ196196 and PZ196197). Pathogenicity was tested by brushing conidial suspensions (1 × 10⁶ conidia/mL) onto basal stems of one-year-old healthy P. thomsonii plants, followed by Parafilm wrapping. Controls received sterile water. Each isolate was tested on six plants per replicate, with three replicates. All plants maintained under greenhouse conditions developed typical symptoms 6 days post-inoculation, while controls remained asymptomatic. Re-isolations from symptomatic tissues yielded fungi identical to the original isolates based on morphology and multilocus sequences, fulfilling Koch’s postulates. To our knowledge, this is the first report of stem base rot on P. thomsonii caused by a complex of Fusarium pseudensiforme and Fusarium suttoniana in China. This finding establishes a pathogen complex in kudzu root production regions, providing a basis for disease surveillance and integrated management.