Discovery of a Root-Lesion Nematode, Pratylenchus scribneri, Infecting Corn in Inner Mongolia, China

Corn (Zea mays L.) is one of the most important crops in China, with over 34.94 million hectares cultivated annually (Li et al. 2014). The root-lesion nematode, Pratylenchus scribneri Steiner, 1943, is an important plant-parasitic nematode that invades roots of many crops. In August 2017, five root and soil samples were collected in a corn field in Chifeng city of Inner Mongolia, China. The samples were taken from poorly growing corn plants (cv. Fengtian No. 11), and distinct brown lesions similar to those caused by root-lesion nematodes were observed on the roots. Root-lesion nematodes were extracted with the modified Baermann funnel method (Hooper et al. 2005). On average, 513 root-lesion nematodes per kilogram of soil were extracted. The nematodes were sterilized with streptomycin sulfate and reared on carrot disks at 25°C. Corn (cv. Fengtian No. 11) plants were grown in 2.0-liter pots containing 1.8 liters of sterilized soil in a greenhouse maintained at 25°C, and eight plants (pots) were inoculated with 2,000 root-lesion nematodes. At 12 weeks after nematode inoculation, the plants were harvested, the roots were washed, and brown lesions were observed on the roots. Root-lesion nematodes in the soil and roots were extracted as previously described (Hooper et al. 2005). The final nematode population density was 7,510 in soil and 1,275 in roots, indicating a substantial increase in the number of root-lesion nematodes. Nematodes were examined morphologically and molecularly for species identification. Morphological measurements of adult females (n = 16) included body length, which ranged from 436.5 to 536.0 μm (mean 510.0 μm), head with two lip annuli, stylet length from 14.0 to 17.0 μm (mean 15.0 μm), tail length from 23.5 to 29.5 μm (mean 27.0 μm), a = 24.7 to 29.8 μm (mean 26.9 μm), b = 4.7 to 6.8 μm (mean 5.7 μm), c = 17.0 to 20.9 μm (mean 19.0 μm), and V = 76.4 to 79.1% (mean 77.6%). No males were found in the samples. The morphological characters of this population are consistent with those described for P. scribneri (Castillo and Vovlas 2007). DNA was extracted from one individual female using liquid nitrogen, followed by proteinase K–based lysis (Wang et al. 2011). The 28S D2/D3 region and internal transcribed spacer (ITS) region were amplified using primers D2A/D3B (5′-ACAAGTACCGTGAGGGAAAGTTG-3′/5′-TCGGAAGGAACCAGCTACTA-3′) (Subbotin et al. 2006) and primers 18S/26S (5′-TTGATTACGTCCCTGCCCTTT-3/5′-TTTCACTCGCCGTTACTAAGG-3′) (Vrain et al. 1992), respectively, and then cloned and sequenced. The obtained sequences of the D2/D3 region of 28S rRNA gene (785 bp) and ITS region (1,101 bp) in this study were submitted to GenBank. The ITS sequence (accession no. MK208689) exhibited 98% identity with P. scribneri sequences (KX842626, KT873860, KY424229, and KY424227), whereas the D2/D3 region of 28S rRNA gene (MK209593) had a 100% identity with P. scribneri sequences available from GenBank (KY424300, KX842628, KX842625, and JX047001). Both morphological and molecular data confirmed the identity of P. scribneri. P. scribneri has been reported on corn in Hebei, Shanxi, Henan, Shandong, Jiangsu, and Liaoning provinces of China (Gao et al. 1992; Liu et al. 1996). Han et al. (2018) reported Pratylenchus sp. from corn roots and soil in Inner Mongolia; however, the species was not identified. To our knowledge, this is the first report of P. scribneri on corn in Inner Mongolia, China.