First Report of Southern Root-Knot Nematode (Meloidogyne incognita) on Maize in Shandong Province of China

Abstract

Maize (Zea mays L.) is an important cereal crop globally for food, livestock feed, and raw material for industries. In July and August 2019, patches with poorly developed maize plants were observed in Weifang, Shandong Province, China. Typical root-knot nematode (RKN) symptoms such as stunting and galled roots were observed. Females, males, second-stage juveniles (J2s), and eggs were collected for morphological identification. The perineal pattern of females had a high dorsal arch, which was square or trapezoid and mostly lacking obvious lateral lines. Measurements of females (n = 20): body length (L) = 613.01 ± 68.45 µm (472.38 to 732.11 µm); maximum body width (W) = 381.30 ± 21.92 µm (328.22 to 421.76 µm); stylet length (ST) = 15.75 ± 1.65 µm (13.7 to 19.58 µm); stylet knob height (STKH) = 1.68 ± 0.13 µm (1.51 to 2.06 µm); stylet knob width (STKW) = 3.84 ± 0.32 µm (3.29 to 4.36 µm); and distance from dorsal esophageal gland opening to the stylet knob (DGO) = 3.55 ± 0.26 µm (3.01 to 3.97 µm). Measurements of males (n = 20): L = 1,385.35 ± 144.77 µm (1,061.14 to 1,617.03 µm); W = 35.50 ± 4.24 µm (24.66 to 41.47 µm); L/W = 39.40 ± 4.95 (31.12 to 50.49); L/distance from body anterior end to junction of esophagus and intestine = 14.71 ± 1.59 (11.41 to 17.34); ST = 20.11 ± 1.78 µm (17.32 to 23.34 µm); STKH = 2.70 ± 0.62 µm (1.25 to 3.75 µm); STKW = 3.68 ± 0.71 µm (2.03 to 4.63 µm); DGO = 3.52 ± 0.36 µm (2.72 to 3.98 µm); and spicule length = 29.92 ± 2.40 µm (22.1 to 32.91 µm). Measurements of J2s (n = 20): L = 396.21 ± 18.25 µm (360.94 to 425.45 µm); W = 13.75 ± 1.12 µm (11.63 to 15.73 µm); L/W = 28.93 ± 1.52 (25.83 to 31.67); L/distance from body anterior end to junction of esophagus and intestine = 5.86 ± 0.12 (5.63 to 6.04); ST = 10.05 ± 0.88 µm (8.69 to 11.53 µm); STKH = 1.30 ± 0.10 µm (1.15 to 1.47 µm); and DGO = 2.36 ± 0.13 µm (2.07 to 2.56 µm). Measurements of eggs (n = 20): L = 80.80 ± 6.60 µm (69.59 to 95.28 µm); W = 33.70 ± 5.63 µm (23.23 to 44.91 µm); and L/W = 2.45 ± 0.35 (1.97 to 3.07). Morphological characteristics were consistent with Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949. DNA was extracted from mature females (Castagnone-Sereno et al. 1995). The D2-D3 region of the 28S rDNA was amplified with universal primer pair D2A/D3B and directly sequenced (Al-Banna et al. 2004). The resulting sequence was deposited in GenBank (MN847618); it had >99% identity with other sequences of M. incognita. For confirmation, M. incognita-specific primer pair IncK-14F/IncK-14R was used for amplification of a sequence characterized amplified region (Randig et al. 2002). A ∼400-bp amplification product was observed under UV light. There were no bands obtained for M. javanica using the above primers. Based on morphological and molecular data, the RKN from maize was identified as M. incognita. A pathogenicity test was carried out by inoculating 1,000 J2s to pots containing 2-week-old maize; 15 plants were inoculated, and four noninoculated plants served as controls. Plants were maintained in a greenhouse at 25 to 28°C. Seven weeks after inoculation, all of the inoculated roots had galling symptoms similar to those observed in the field; the root gall index was ∼5 according to a 0 to 10 RKN rating scale (Bridge and Page 1980). No symptoms developed on the controls. M. incognita is one of the most devastating sedentary endoparasites infecting roots of a wide range of crop plants worldwide (Alioto et al. 2015). The use of appropriate rotation crops is important for the management of RKNs. In China, maize was usually recommended in crop rotation as a nonhost crop for the management of RKNs in some cropping systems. However, the detection of this nematode on maize in China indicates that using maize in crop rotation systems may limit the effectiveness in managing RKNs. The findings are significant for integrated management of RKNs, particularly for crop rotation. To our knowledge, this is the first report of M. incognita parasitizing Z. mays in Shandong Province. Further monitoring and control strategies should be followed.