First report of southern root-knot nematode, Meloidogyne incognita, infecting pomegranate, Punica granatum, in Peru

Abstract Punica granatum plants showing symptoms caused by root-knot nematodes were detected in the municipality of Majes, Arequipa, Peru. Based on the morphological, esterase phenotypes, and molecular analyses of the mitochondrial DNA region between the cytochome oxidase subunit II and 16 S rRNA genes (mtDNA) and species-specific sequence characterized amplified region, the causal agent of the observed symptoms was identified as Meloidogyne incognita. Pathogenicity was confirmed by fulfilling a modified version of Koch’s postulates. To our knowledge, this is the first report of M. incognita infecting P. granatum in Peru.

Pomegranate (Punica granatum L.) is an exotic fruit in Peru that has unique pharmacological characteristics including several bioactive compounds. Its cultivation is intended for ornamentation, fruit production for fresh consumption, or processed products, such as juices, syrups, and jellies (Saroj et al., 2008), among others.
Plants can be attacked by pests, diseases, and plant-parasitic nematodes, which can qualitatively and quantitatively impair production (Dias-Arieira et al., 2010;Sikora et al., 2018). Among the plantparasitic nematodes, the most important the genus is Meloidogyne Göldi, 1887, which causes damage in the form of root galls and reduction in the number of roots, and predisposition to fungal and bacterial diseases causing losses in crop yields (Karssen, 2002;Sikora et al., 2018). Furthermore, root-knot nematodes often thrive and cause damage on perennial hosts for many years preventing them from reaching their full yield potential. The root-knot nematodes, Meloidogyne incognita (Kofoid and White, 1919;Chitwood, 1949) and M. javanica (Treub, 1885;Chitwood, 1949), the economically important parasites of pomegranate cultivars in the world (Singh et al., 2019).
In a six-year-old pomegranate (cv. Wonderful) plantation aged six years old in Majes, Arequipa, Peru (16°19´37.0˝S; 72°13'08.0"W), plants after pruning were slow to develop new shoots ( Figure 1A) and roots with distinct galls ( Figure 1B-D) were collected on September, 2019. In order to identify the plantparasitic nematode species, a combination of morphological, biochemical, and molecular analyses were performed.
In greenhouse tests, P. granatum (cv. Wonderful) plantlets were maintained in pots with 5,000 dm 3 sterilized soil. In total, eight replicates were inoculated with 5,000 eggs and J2s from the original population of M. incognita, in addition to a non-inoculated control. Plants were well maintained under greenhouse JOURNAL OF NEMATOLOGY Figure 2: A-C: Meloidogyne incognita (Kofoid and White, 1919;Chitwood, 1949) perineal patterns detected in Punica granatum L. (cv. Wonderful) (Scale for light microscopy photos = 10 μ m).
conditions at 25 ± 3°C. After 120 days, the inoculated plants exhibited galled root systems similar to plants observed in the field, with a nematode reproduction factor (final population/initial population) of 18.5. The non-inoculated plants did not exhibit any galls. The morphological and molecular characterization of this re-isolated root-knot nematode were identical those of M. incognita. This is the first report of M. incognita parasitizing pomegranate plants in Peru. This finding has great importance for the fruit, and nursery industry in Peru, since this nematode may damage pomegranate plants and become more widespread and a significant problem for this crop.