First Report of Rotylenchulus reniformis on Tomato in Henan, China

The reniform nematodes of the genus Rotylenchulus infect over 300 species from numerous plant families in tropical, subtropical, and warm-temperate regions (Redding et al. 2018; Robinson et al. 1997). Rotylenchulus reniformis Linford & Oliveira, 1940 is the most economically significant species in the genus and parasitizes a wide variety of crops, such as cotton, soybean, several tropical fruit species, and vegetable crops including tomato (Redding et al. 2018; Robinson et al. 1997; Van Den Berg et al. 2016). Tomato is one of the most widely cultivated vegetables in China. In 2016 and 2017, a survey for plant-parasitic nematodes attacking tomato was performed in tomato fields near Huixian City, Henan Province, in central China. Tomatoes were stunted and yields were reduced. Roots systems of sick plants were poorly developed. Soil and root samples were randomly collected from 30 locations, and the samples were taken from one 34-ha field. Soil samples were collected at a depth of 5 to 25 cm. Nematodes were isolated from soil using the sugar centrifugal flotation method. The washed root pieces were cut into 0.5-cm sections, thoroughly mixed, and macerated in an extraction dish to nematode extraction (Gowen et al. 2005; Zhang et al. 2016). Rotylenchulus spp. were found in all of the samples with population densities ranging from 13 to 32 nematodes per gram of root and 231 to 1,587 nematodes per kilogram of soil. Nematodes were identified as R. reniformis according to morphological and molecular analysis (Palomares-Rius et al. 2018; Van Den Berg et al. 2016). Morphological identification was conducted based on characteristics of preparasitic adult females such as body shape, labial region, stylet length, vulva location in relation to body length (V ratio), and tail shape. The body of immature females (n = 29) was vermiform. Labial region continuous with body contour. Stylet with rounded basal knobs. More posterior position of the vulva and conoid tail. Body length was 0.43 mm (0.37 to 0.48), stylet of 17.6 μm (15.8 to 18.9), and a vulva at 69.7% (66.8 to 73.0%), De Man ratios (Castillo and Vovlas 2007) were as follows: a = 25.2 (22.1 to 28.5), b = 3.5 (3.0 to 3.9), b′ = 3.0 (2.6 to 3.5), c = 16.9 (14.2 to 20.7), and c′ = 2.8 (2.1 to 3.3). Males (n = 21) had weak stylets and stylet knobs, and the esophagus and median bulb were reduced. Additionally, the internal transcribed spacer (ITS)-rDNA region was used to molecularly identify this nematode. DNA was extracted from 25 nematodes, and the ITS-rDNA region was amplified using forward primer CGTAACAAGGTAGCTGTAG and reverse primer TCCTCCGCTAAATGATATG (Ferris et al. 1993). The polymerase chain reaction product was purified and sequenced. The sequence was compared with those in NCBI’s nucleotide database by a BLAST search. The comparison revealed a sequence identity of 99% with R. reniformis (GU003938.1 and KP018562.1). To fulfill modified Koch’s postulates, the R. reniformis described in this study was used in a greenhouse assay to confirm reproduction on tomato. Tomato cultivar Moneymaker in five pots was used in greenhouse assay; each tomato was inoculated with 300 R. reniformis of mixed life stages. Five additional tomato plants were not inoculated with R. reniformis and served as a control. Plants were maintained in the greenhouse at 27°C, and 10 weeks later, the reproduction factors (final population/initial population) ranged from 7.5 to 16.9. R. reniformis was not observed on control plants. R. reniformis parasitism resulted in high levels of necrosis along the roots. No such symptoms were observed in the control plants. This is the first report of R. reniformis parasitizing tomato in Henan Province, China. Additional work is needed to elucidate the prevalence of this nematode in the province.