First report of Meloidogyne graminicola on rice in Anhui province, China.

Abstract

Meloidogyne graminicola, a devastating plant pathogen of rice (Oryza sativa), is considered to a severe constraint to productivity in rice-growing areas (Zhan et al., 2018). In April 2020, irrigated paddy rice field in Qianshan City, Anhui Province, China, showed symptoms with stunting, thinning, chlorosis, and typical hook-shaped root tips. Females and egg masses of Meloidogyne sp. were found inside the cortex of the root galls, males were found in soil and roots. The morphological characteristics of females, males and second-stage juveniles (J2) were identified as described previously (Tian et al., 2017; Wang et al., 2017). The perineal pattern of the females (n=12) was dorsoventrally oval with low and round dorsal arches, with lateral fields obscure or absent. Most of the striae were smooth, and occasionally broken by short and irregular striae. Morphological measurements (mean±sd, range) of female nematodes (n=20) were body length (543.0±66.0 µm, 448.0-629.0 µm), stylet (11.6±1.9 µm, 7.9-14.2 µm), dorsal pharyngeal gland orifice to stylet base (DGO) (4.0±0.4 µm, 3.4-4.7 µm), vulval slit length (24.1±4.9 µm, 14.8-32.8 µm), vulval slit to anus distance (16.1±3.0 µm, 8.4-20.2 µm). The male nematodes were cylindroid, vermiform, and rounded tail, with the measurements (n=20) body length (1673.0±125 µm, 1346.0-1822.0 µm), stylet (15.5±0.8 µm, 14.0-17.1 µm), DGO (3.7±0.5 µm, 2.9-5.5 µm), and spicule (30.7±2.5 µm, 23.4-34.6 µm). The J2 were vermiform with a gradually tapering hyalines, its measurements (n=20) were body length (452.0±33.0 µm, 391.0-511.0 µm), stylet (13.4±0.8 µm, 12.0-15.2 µm), DGO (3.6±0.6 µm, 2.5-4.7 µm), tail length (72.1±5.2 µm, 59.8-84.8 µm) and hyaline tail terminus (21.7±2.5 µm, 18.0-29.7 µm). DNA extracted from individual females (n=10) were used for molecular identification. The D2/D3 region of 28S RNA was amplified with D2A (5'-ACA AGT ACC GTG AGG GAA AGT TG-3') and D3B (5'-TCG GAA GGA ACC AGC TAC TA-3') (De Ley et al. 1999). The ITS region was amplified with AB28 (5'-ATA TGC TTA AGT TCA GCG GGT-3') and TW81 (5'-GTT TCC GTA GGT GAA CCT GC-3') (Curran et al. 1994). The fragments of D2/D3 region (GenBank accession No. MT576694) and ITS region (GenBank accession No. MT573412) were 766 bp and 579 bp respectively, they all exhibited 99%-100% similarity with those of M. graminicola isolates available in the GenBank. Therefore, both morphological and molecular characterization confirmed the status of this nematode as Meloidogyne graminicola. In green house test, twenty 2-week-old rice seedlings (cv. Longliangyou) were individually maintained in pots with sterilized sand and soil (3:1) and inoculated with 300 J2, other ten non-inoculated rice seedlings as negative control. Rice seedlings were grown in green house at 28℃/25℃ with a 16 h/8 h light/dark photoperiod. After 30 days, all inoculated rice seedling showed symptoms with stunting, chlorosis, and typical hook-shaped root tips, which were similar with that in fields. The nematode reproduction index (final population density/initial population density) were 7.86-10.32. No symptoms were observed on non-inoculated rice seedlings. These results confirmed the pathogenicity of M. graminicola on rice. To our knowledge, this is the first report of M. graminicola in Anhui Province, China. References Curran, J., et al. 1994. Mycol. Res. 98:547. https://doi.org/10.1016/S0953-7562(09)80478-4. De Ley, P., et al. 1999. Nematology. 1:591. https://doi.org/10.1163/156854199508559. Tian, Z., et al. 2017. Plant Disease. http://dx.doi.org/10.1094/PDIS-06-17-0832-PDN. Wang, G., et al. 2017. Plant Disease. http://dx.doi.org/10.1094/PDIS-12-16-1805-PDN. Zhan, L., et al. 2018. BMC Plant Biol. 18:50. https://doi.org/10.1186/s12870-018-1266-9.