First Report of Meloidogyne enterolobii Yang & Eisenback, 1983 (Guava Root-knot Nematode) Infecting Guava (Psidium guajava) in Egypt.

Abstract

Meloidogyne enterolobii Yang & Eisenback, 1983 (guava root-knot nematode) is an important disease in subtropical to tropical climate in several areas of the world (Subbotin et al., 2021). It is a highly polyphagous root-knot nematode species causing major damage to a range of economically important crops. The expansion of this species is increasing worldwide creating a potential problem to the maintenance of resistance genes to other major Meloidogyne species (Castagnone-Sereno and Castillo, 2020). Additionally, the diagnosis of M. enterolobii can be challenging due to morphological similarities with other root-knot nematode species (Castagnone-Sereno, 2012). In the African continent, it has been cited in several countries of Equatorial and South Africa (Subbotin et al., 2021), but not in North Africa. Two guava groves (at Bany Salama, Natrn vally, El Beheira governorate, 30.322043N, 30.518529E; and Izbat Al Halawijah, Monshaah Alaweyah, Abu El Matamir, El Beheira governorate 30.9398050N, 30.1484430E), in Egypt, were found with significant symptoms of tree decline and root galling damage. The presence of egg masses and females of root-knot nematodes were found inside the galls (Figure 1A, B). Nematodes were extracted from soil samples with levels of 12300 and 12600 second-stage juveniles (J2s)/250 g of soil using a modified Baerman method (Hooper, 1986), respectively. Nematode root density was 24367 eggs/g of root, using the protocol described in Hussey and Barker (1973) for Izbat Al Halawijah population. For morphological and morphometrical identification, J2s and females were fixed using a hot formalin solution (4% v/v). DNA was isolated from single J2s specimen for: i) testing multiplex specific-PCR assay for M. incognita, M. javanica and M. arenaria (Kiewnick et al., 2013), and ii) amplifying and sequencing of cytochrome oxidase subunit II (COII) and the 16S rRNA mitochondrial region using the primer pair C2F3 (5'-GGTCAATGTTCAGAAATTTGTGG-3') (Powers and Harris, 1993) and MRH106 (5'- AATTTCTAAAGACTTTTCTTAGT-3') (Stanton et al., 1997). Perineal patterns of females for Izbat Al Halawijah population were typical of the species (Fig. 1D), body size (L: 520-774 µm; W: 214-487 µm), stylet length (12.5-13.7 µm) and ratio from distance from anterior end to excretory pore and stylet length (4.2) in females (n = 18), fitting with original description and others (Subbotin et al., 2021). J2s from Izbat Al Halawijah population (n=13) (Fig. 1C, E-H) showed: body length (393.5-475 µm), stylet length (11.5-13.5), excretory pore to anterior end (89-95.5 µm), tail length (50.0-60.0 µm), tail hyaline region (12.0-21.0 µm), a ratio (24.2-32.5), b ratio (4.9-6.5), c ratio (7.3-8.6) and c' (5.0-6.4), also fitting with original description and others (Subbotin et al., 2021). Specific PCR did not amplify any band (Kiewnick et al., 2013). Four J2s individuals were sequenced for COII-16S rRNA region for each population showing M. enterolobii as unique species and without intraspecific variability. Two identical DNA fragments of 814 bp obtained for both populations (OP434400 and OP434401) were compared with those in GenBank. A BLAST search indicated the sequences were 100% identical to several sequences of M. enterolobii (MF467278 and KX823371). On the basis of these results, the root-knot nematodes isolated from these two guava groves in Egypt were confirmed as M. enterolobii. This is a well-known pathogen of guava, causing important losses in this crop (Castagnone-Sereno and Castillo, 2020) and it is regulated as quarantine nematode in the Mediterranean region (EPPO).