First Report of <i>Ditylenchus destructor</i> Infesting Sweet Potatoes in Hunan Province, China

Sweet potato (Ipomoea batatas) is a vital food crop, with China accounting for 29.8% of global planting area and 53.6% of total production (Xu. et al., 2024). In early November 2023, a survey in Yongshun County, Hunan Province (29.01°N, 109.90°E), found that approximately 5% of sweet potato tubers within an 800 m² cultivation area were diseased. The diseased tubers exhibited surface browning with cracks, dark brown necrosis tissue upon cross-sections, and punctate voids indicative of dry rot. Microscopic examination confirmed endoparasitic nematodes in the affected tissues. After nematode isolation and purification, morphological and molecular methods were employed for identification. Morphologically, the nematodes showed slightly ventral curvature, linear, translucent bodies, and lateral fields with six incisures. The basal pharyngeal bulb overlapped dorsally with the intestine. Females exhibited a postvulval uterine sac approximately three-quarters the length of the vulva-anus distance, and tails terminating in a finely rounded cone. Males were slenderer, with narrower, pointed-round tails, curved hook-like spicules, and a bursa extending to three-fourths of the tail length without reaching the tip. Female morphometric measurements (mean ± SD; n = 25) were as follows: body length (L)= 1620.8 ± 110.6 μm, body width (W) = 45.1 ±9.0 μm, stylet length = 10.9 ± 0.8 μm, tail length = 114.8 ± 18.3 μm; De Man indices: a (body length / greatest body diameter) = 36.9 ± 5.5, b (body length / distance from anterior to esophago-intestinal valve) = 7.5 ± 0.7, c (body length / tail length) = 14.4 ± 1.9, V (% distance of vulva from anterior) = 79.8 ± 2.5. Male measurements (mean ± SD; n= 25) included: L = 1084.2 ± 124.0 μm, W =29.6 ± 5.8 μm, stylet length =11.7 ± 0.6 μm, tail length =74.8 ± 7.6 μm, a = 37.2 ± 3.9, b = 8.0 ± 0.8, c = 14.5 ± 0.6, spicule length = 34.1 ± 4.2 μm. These characteristics closely match the original description of D. destructor by Brzeski (1991). Molecular identification involved amplification of the ribosomal ITS region using universal primers ITS-P1/P2 (Ni. et al. 2023), with sequences subsequently deposited in GenBank (accession nos. PQ607770, PV270004, and PV276810). A Maximum Likelihood phylogenetic tree constructed in MEGA11 placed the sequences within the D. destructor clade with 96% bootstrap support. Additionally, PCR using genotype B-specific primers DdL1/DdL2 (Wan. et al. 2008) produced a specific 485 bp band on 1.5% agarose gel, confirming the genotype. A pathogenicity test was conducted in a greenhouse (25–32 ℃) using Yanshu 25 (I. batatas) plants in 30 × 20 cm pots. Each of five replicate pots was inoculated with 5,000 mixed-stage nematodes, with non-inoculated pots serving as controls. After 90 days, tubers from inoculated plants showed blackened, brown, and spongy peridermis and cortex, whereas controls remained asymptomatic. The nematode reproduction factor (final population/initial population) was 5.45 ± 0.64, confirming pathogenicity. Based on analysis of morphological characteristics, molecular identification, and pathogenicity tests, the Yongshun population was confirmed as D. destructor genotype B. In China, prior reports of D. destructor on sweet potato were limited to northern provinces. To our knowledge, this is the first report of D. destructor infecting sweet potato in Hunan (southern China), indicating the southward range expansion. Enhanced monitoring, quarantine, and control strategies are recommended.