First Report of Cereal Cyst Nematode, <i>Heterodera australis</i>, in Wheat in Shaanxi, China

Cereal cyst nematodes <i>Heterodera</i> spp., are important pathogens of wheat (Toumi et al. 2018). Among these species, members of the Avenae group including <i>H. avenae</i> and <i>H. filipjevi</i>, are widely distributed worldwide, while <i>H. australis</i>, a species originally identified in Australia (Subbotin et al. 2002), is mostly restricted to Australia. In 2011, a single report documented the detection of <i>H. australis</i> in Henan Province, China (Fu et al. 2011), with no subsequent detections reported since. In the spring of 2024, a survey covering 60 sites was conducted in the wheat production area of central Shaanxi Province, China. Cyst nematodes were found on wheat roots and in adjacent soil. Molecular tools were used for species identification. DNA was extracted from a single cyst at each sampling site, and PCR was performed to amplify the internal transcribed spacer (ITS) region, 28S D2/D3 expansion segments of ribosomal RNA genes, and cytochrome c oxidase subunit 1 mitochondrial gene (mtCOI) (primer sets D2a/D3b, TW81/AB28, and JB3/JB5, respectively) (Bowles et al. 1992; De Ley et al. 1999; Maafi et al. 2003). PCR products were purified and sent for Sanger sequencing. The resulting sequences were compared against the NCBI database using BLAST. Most samples were identified as <i>H. avenae</i>. However, cysts from two adjacent sites in Huyi District, Xi'an, showed over 99% sequence similarity to <i>H. australis</i> across all three genes (GenBank accession number: 28S: PQ620113; ITS: PQ620118; mtCOI: PQ596186). The identification was confirmed through at least three independent analyses. We subsequently measured the morphological features of these nematodes. Second-stage juveniles (n = 15) had body lengths ranging from 524.19 to 602.71 μm, stylet lengths (including basal knobs) from 24.41 to 26.52 μm, true tail lengths from 58.39 to 67.12 μm, hyaline tail terminal lengths from 34.15 to 46.53 μm, body widths from 19.09 to 21.84 μm, and tail widths ranging from 13.35 to 16.60 μm. Cyst measurements (n = 14) included body lengths (including the neck) ranging from 655.71 to 938.81 μm, body widths from 431.76 to 588.14 μm, neck lengths from 55.08 to 133.43 μm, fenestra lengths from 39.65 to 58.34 μm, fenestra widths from 18.88 to 29.62 μm, and vulval slit lengths from 8.20 to 13.13 μm. These results generally agree with the original description of <i>H. australis</i> (Subbotin et al. 2002). We performed pot experiments in a greenhouse at 20°C. Eggs were inoculated onto roots of 7-day-old wheat plants (cultivar "Xinong106"). Third-stage juveniles were observed 15 days post-inoculation in the wheat roots, stained using the acid fuchsin method (Bybd et al. 1983), and cysts were observed 53 days post-inoculation. Thus, through molecular and morphological methods, we report the first detection of <i>H. australis</i> in Shaanxi Province, China, suggesting its extended distribution into northwestern China, based on the earlier report from Henan Province (Fu et al. 2011). Further work is required to investigate the epidemiology of <i>H. australis</i> and to better understand its impact on wheat production in Shaanxi.