Pequi is a Host for Pratylenchus zeae in the Brazilian Cerrado Region

The Brazilian Cerrado Region has many natural resources that have high social economic interest. Pequi (Caryocar brasiliense Camb.), a native species from that area, has an edible fruit, which is highly appreciated by the local population, and also a high-quality wood. In January 2010, pequi root samples were collected near the municipality of Rio Verde, Goiás State, Brazil (17°49'25.76″S, 51°02'10.06″W). Roots were washed with tapwater, dried on absorbent paper, cut in 1-cm² pieces, and processed for nematode extraction by the blender centrifugal flotation method (2). The specimens were identified by morphological and morphometrical characteristics of six adult females mounted in formaldehyde temporary slides (1). Morphological characters used for identification included female body, stylet, pharyngeal overlapping, pharynges, postvulval uterine sac, tail lengths, stylet knobs, number of labial rings, vulva position in relation to body length, body diameters (high body, vulval, and anus region), and the de Man's ratios (a, b, b', c, and c'). Characters measured were consistent with those described for Pratylenchus zeae Graham, 1951 (1); the labial region showed three annuli, stylet was 14.83 (±0.93) μm long, with broad, anteriorly flattened basal knobs. Vulva position was 71.66% (±0.98) of body length and spermatheca was round, small, and without sperm (males were not found). Postvulval uterine sac was short (31.3 ± 4.03 μm) and tail (26.6 ± 3.61 μm) was conoid, pointed, and unstriated. Pharyngeal overlapping length was 30.5 (±6.5) μm; pharynges were 150.83 (± 28.16) μm long. The de Man's ratios obtained were: a = 24.26 ± 2.31; b = 3.89 ± 0.69; b' = 3.08 ± 0.48; c = 17.17 ± 1.47; and c' = 2.25 ± 0.19. To our knowledge, this is the first report of P. zeae infecting pequi. It is difficult to determine the economic importance of this nematode parasite to pequi production since pequi is not yet a commercial crop in Brazil. This finding, however, has long term importance because researchers have been developing improved cultivars by combining favorable agronomic characteristics with high oilseed content for biofuel production. If these are commercialized, P. zeae could become an important pathogen in pequi plantings. References: (1) P. Castillo and N. Vovlas. Pratylenchus (Nematoda: Pratylenchidae): Diagnosis, Biology, Pathogenicity and Management. Koninklijke Brill NV, Leiden, the Netherlands, 2007. (2) W. A. Coolen and C. J. D'Herde. A Method for the Quantiative Extraction of Nematodes from Plant Tissue. State Agric. Entomol. Res. Stn. Ghent, Belgium, 1972.