First Report of Meloidogyne incognita on Mulberry in Saudi Arabia.

Abstract

The genus Morus comprises many species (Suttie 2012). The species Morus alba is one of the most popular mulberry species worldwide. In October 2020, numerous mulberry trees presented chlorotic leaves and stunted growth with severe root galling in a private compound in Riyadh region, Saudi Arabia. The infected roots showed galls, which are typical symptoms of infection by root-knot nematodes (RKNs). Infected roots were dissected, and males and females were extracted from roots while second stage juveniles (J2s) were from both soil and eggmasses. Morphological and morphometrical features were documented. Perineal patterns of females, males, and J2s were studied using a compound microscope. The endoparasitic females had pearly shaped bodies with projecting neck. Stylet knobs were rounded and set off and the shape of the cone distinctly curved. The posterior perineal had a dorsally high square arch. Striae patterns were zig-zag or forked along the lateral lines. Males were vermiform and the head cap flat to concave. Mostly conus of stylet was longer than shaft. Stylet knobs were prominent, set off, flat and usually greater width than the length. Males had a bluntly rounded tail, spicules were slightly curved and gubernaculum was crescentic. The J2s were vermiform, and stylet knobs were prominent and rounded shape. The J2s tail had a transparent area with an obtuse tip. The morphological measurements (means and range) of the perineal patterns of females (n = 4) were: length of vulval slit (LVS) = 22.5 (21.5 to 23.4) μm, anus to vulval slit (AVS) = 22 (21.8 to 22.1) μm, and anus length (AL) = 7.7 (7.5 to 7.8) μm. The males (n = 16) measurements were: length (L) = 1136 (1116 to 1159) μm; a (total body length / greatest body width) = 34.8 (33 to 37.1); body width = 32.7 (31.2 to 33.8) μm; stylet length = 25.6 (24.7 to 27.3) μm; dorsal oesophageal gland orifice (DGO) = 2.9 (2.6 to 3) μm, tail length = 7.1 (6.5 to 7.8) μm, c (total body length / tail length) = 161 (143.1 to 175), spicules length = 30.8 (26 to 33.8) μm; gubernaculum = 9.7 (9.1 to 10.4) μm. The J2s (n = 11) measurements were: L = 395 (378 to 405) μm; a = 26.2 (24.3 to 28.4); c = 8.6 (8.2 to 9.2); head end to metacorpus valve = 53 (49.4 to 54.6) μm; excretory pore to head end = 78 (72.8 to 80) μm, stylet length = 10.7 (10.4 to 11.7) μm; body width = 15.1 (14.3 to 15.6) μm; tail length = 45.8 (44.2 to 49.4) μm; hyaline tail terminus length = 12.5 (10.4 to 13) μm. Both the morphological and morphometrical features of the perineal pattern of the females, males, and J2s match the original description of Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949 (Eisenback and Hirschmann 1981; Taylor and Netscher 1974). To perform Koch's postulates, mulberry plants maintained in pots were inoculated with 2,500 J2s and eggs of the original population of M. incognita using five replicates. After two months, all inoculated plants had galled roots typical of RKNs. Reproduction factor value was 6.4. The noninoculated plants did not present galls in the roots. These results confirmed the nematode's pathogenicity on mulberry. To the best of our knowledge, this is the first report that M. incognita was identified as a parasite of mulberry (Morus alba) in Saudi Arabia and the world, while Meloidogyne hispanica was reported on mulberry trees in Iran (Shokoohi et al. 2016). The importance of this report shed some lights on this new problem to direct the attention of farmers and home gardeners to take actions for the management of this newly identified problem. The authors declare no conflict of interest. Acknowledgments Authors wish to thanks College of Food and Agricultural Sciences, Research Center and Deanship of Scientific Research, King Saud University, Saudi Arabia for supporting this work.