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

The peach tree (Prunus persica) is the third most cultivated temperate fruit species in Brazil. In August 2017, peach seedling plants showing symptoms of stunting and multiple galls in the roots were detected in the municipality of Pelotas, state of Rio Grande do Sul, Brazil. Samples of peach roots were collected and they were subsequently processed to obtain eggs and second-stage juveniles (J2), to determine the number of nematodes per gram of roots and to proceed with morphological studies. Additionally, individual females were extracted from the peach roots and submitted to Meloidogyne species identification by electrophoresis using α-esterase (Est) and malate dehydrogenase (Mdh) phenotypes and perineal pattern. The nematode population density in the samples was 283 eggs + J2s per gram of fresh roots. The polymorphism analysis revealed the A3N1 phenotype, typical to Meloidogyne morocciensis. Perineal patterns of females showed oval squared shapes, with moderately high to high dorsal arches, streaks widely separated, generally continuous, sometimes broken; the phasmids were separate by 29.3 μm (25.43-31.94 μm), similar to M. arenaria and M. incognita, as observed by Hammah and Hirschmann (1990). The second-stage juveniles had the following morphometric characters: L = 389.3 ± 3.8 (377.5-425.1) μm, stylet = 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 = 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 is the same as that amplified for M. morocciensis. Under greenhouse conditions, peach plants seedlings inoculated with 1,000 eggs (Pi) with M. morocciensis were evaluated 28 days after inoculation compared to non-inoculated plants. The inoculated peach plants showed a mean of 338 galls per root system, and a nematode reproduction factor of 10.3. Besides this plants exhibited a reduction in fresh weight of shoots and roots compared to the non-inoculated plants. These results confirm M. morocciensis pathogenicity on P. persica.