Discovery of Root-Lesion Nematode, Pratylenchus coffeae, Infesting Sesame in China

Abstract

Sesame (Sesamum indicum L.) is one of the most important oil crops in China. Root-lesion nematodes (Pratylenchus spp.) are one of the most important groups of plant-parasitic nematodes parasitizing many crops. In September 2017, a survey of root-lesion nematodes was carried out in a sesame field in Xuchang city, Henan Province of China. Samples from six plants of sesame cultivar Zhengzhi No.15 were collected about 20 days before harvest. The collected plants were growing poorly with roots that showed distinct brown lesions. Nematodes were extracted using the modified Baermann funnel method (Hooper et al. 2005). Root-lesion nematodes were found in four samples, with the average nematode population density of 461 ± 211.9 nematodes/1 kg of soil and 39 ± 12.3 nematodes/1 g of root. The extracted nematodes were cultured and reared on carrot disks to obtain the nematode inoculum. Seeds of sesame cultivar Zhengzhi No.15 were sown in 1.5-liter pots containing 1.2 liters of sterilized soil. About 25 days after sowing, eight seedlings, one per pot, were inoculated with 2,000 nematodes and maintained in a greenhouse at 25°C. Eleven weeks later, the plants were harvested, and brown lesions were observed on roots. Nematodes from soil and roots were extracted as described above. The final number of root-lesion nematodes averaged 4,316 ± 894.9 in soil and roots, and the reproduction rate was 2.2 ± 0.4. Nematodes were identified morphologically and molecularly. Morphological measurements of females (n = 17) included body length (range = 533.0 to 645.0 μm, mean = 602.0 μm), two lip annuli, stylet (15.0 to 17.0 μm, 16.0 μm), tail length (26.0 to 34.5 μm, 30.5 μm), a (24.2 to 34.6, 27.8), b (5.2 to 6.9, 6.2), c (18.1 to 21.0, 19.7), and V (79.4 to 82.2%, 80.8%). Measurements of males were (n = 17): body length (range = 451.5 to 571.0 μm, mean = 509.5 μm), two lip annuli, stylet (14.5 to 15.5 μm, 15.0 μm), tail length (23.0 to 29.5 μm, 26.0 μm), spicule length (16.5 to 19.0 μm, 18.0 μm), gubernaculum length (4.5 to 5.5 μm, 5.0 μm), a (27.0 to 33.9, 30.9), b (5.6 to 6.6, 6.0), and c (18.3 to 21.3, 19.7). The morphological characters of this population were consistent with those described for Pratylenchus coffeae (Castillo and Vovlas 2007). DNA was extracted from four individual females according to the method of Wang et al. (2011). The rDNA-internal transcribed spacer (ITS) region was amplified by primers 18S and 26S (Vrain et al. 1992). Four ITS sequences were obtained with the length of 1,248 to 1,254 bp. The D2/D3 expansion region of the 28S rDNA was amplified by primers D2A and D3B (De Ley et al. 1999). Four 781-bp D2/D3 sequences were obtained. The polymerase chain reaction products were purified and sequenced. The newly obtained sequences were deposited in GenBank. These ITS sequences (accession nos. MH729035, MN227241, MN588279, and MN588280) showed 99% similarity to several P. coffeae sequences available in GenBank (e.g., KY424205, KC218572, KR106219, and KC244205). The D2/D3 region of the 28S rDNA sequences (MH730447, MN227243, MN588282, and MN592778) showed 99 to 100% similarity to several P. coffeae sequences available in GenBank (e.g., MK829009, KY424274, KY424272, and HM469434). P. coffeae has a wide host range and is widely distributed in China (Jiang et al. 2010). However, there is no report on sesame as a host of Pratylenchus in China. Both morphological and molecular data obtained from this study confirmed the presence of P. coffeae on sesame in Xuchang, China. To our knowledge, this is the first report of P. coffeae on sesame in China.