First report of the root-knot nematode, Meloidogyne morocciensis infecting peach in Southern Brazil

The peach tree (Prunus persica (L.) Batsch) is the third most cultivated temperate fruit species in Brazil. In August 2017, peach seedlings showing symptoms of stunting and multiple galls on the roots (Fig. 1A) were detected in a nursery in Pelotas, Rio Grande do Sul, Brazil. Samples of peach roots were collected and subsequently processed (Hussey and Barker, 1973) to obtain eggs and second-stage juveniles (J2) to determine the number of nematodes per gram of roots and to for morphological studies (n = 20). Additionally, individual females (n = 20) were extracted from the peach roots and identified by electrophoresis using α-esterase (Est) and malate dehydrogenase (Mdh) phenotypes (Carneiro and Almeida, 2001) and perineal patterns (Taylor and Netscher, 1974). The nematode population density in the samples was 283 eggs and J2s per gram of fresh roots. Perineal patterns of females (Fig. 2B,C) showed oval squared shapes, with moderately high to high dorsal arches, striae widely separated, generally continuous, sometimes broken; the phasmids were 29.3 μm apart (25.4-31.9 μm), similar to M. arenaria (Neal, 1889) Chitwood, 1949 and M. incognita (Kofoid and White, 1919; Chitwood, 1949), as observed by Rammah and Hirschmann (1990). The polymorphism analysis revealed the A3N1 phenotype, Est A3 being the phenotype observed for α-esterase with three distinct bands (Rm = 1.11; 1.21; 1.32) (Fig. 1B) and Mdh N1 phenotype corresponding for malate dehydrogenase with only one band (Rm = 1.0) (Fig. 1C), typical to Meloidogyne morocciensis (Rammah and Hirschmann, 1990), according to Carneiro et al. (2008). Measurements and ratios of J2 were as follows in microns as means plus or minus the standard deviation with the range in parentheses (Fig. 2A): L = 389.3 ± 3.8 (377.5-425.1) μm, stylet length = 13.9 ± 0.2 (12.7-14.9) μm, DGO = 3.6 ± 0.1 (3.3-4.2) μm, tail length 47.5 ± 0.6 (45.3-48.9) µm, hyaline tail terminus length = 14.1 ± 0.3 (12.5-17.0) µm, a = 25.6 ± 0.4 (23.8-28.8) µm and c = 8.6 ± 0.1 (8.0-9.3). The known SCAR marker obtained for M. arenaria (Zijlstra et al., 2000) is the same as that amplified for M. morocciensis (Carneiro et al., 2008). Under greenhouse conditions, peach seedlings were inoculated with 1,000 eggs (Pi) from the original population of M. morocciensis, and non-inoculated plants were included. After 180 days, the plants were evaluated for the number of galls in the roots, and the final nematode population was also estimated (Pf). A mean of 338 galls per root system was observed and the nematode reproduction factor (RF = Pf/Pi) was 10.3. Inoculated plants exhibited a reduction in fresh weight of shoots and roots of 17 and 30%, compared to the non-inoculated plants, respectively. These results confirm the pathogenicity of M. morocciensis to peach. Some species of Meloidogyne have already been reported parasitizing peach, with an emphasis on M. incognita and M. javanica (Treub, 1885) Chitwood, 1949 (Carneiro et al., 1993). Although M. morocciensis has been detected in temperate fruit trees such as kiwi (Actinidia deliciosa (Chevalter) Liang and Ferguson) (Somavilla et al., 2011) and grapes (Vitis vinifera L.) (Divers et al., 2019) in Brazil, it is the first report of this species parasitizing P. persica in Brazil. This finding is of great importance for Brazilian agriculture, considering this nematode’s potential harm in the establishment of orchard and its effect on plant growth, fruit production, and the besides affecting plant growth, fruit production, and the longevity of peach trees.

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