First Report of Fusarium equiseti Associated on Pecan (Carya illinoinensis) Seeds in Brazil

Pecan [Carya illinoinensis (Wangenh.) K. Koch] is an important producing nut tree that has been intensively cultivated in the state of Rio Grande do Sul (Brazil) in recent decades. This species is commonly grown in association with other crops and more often with cattle or sheep. An elevated incidence of the fungal genus Fusarium was observed during a quality control seed assay of pecan seeds obtained from orchards in the city of Anta Gorda (28°53'54.7″ S, 52°01'59.9″ W). Concomitantly, seedlings of this species, cultivated in a nursery, showed foliar necrosis, wilt, and root rot. The fungus was thereafter isolated from the seeds (from original seeds lots) and subcultured from single spores. Cultures were purified in order to perform pathogenicity tests. The isolated Fusarium sp. was increased on autoclaved wet corn kernels that were incubated for 14 days (1), and then were mixed with commercial substrate (sphagnum turf, expanded vermiculite, dolomitic limestone, gypsum, and NPK fertilizer) in plastic trays (capacity 7 L), with drainage holes. Twenty seeds were sowed and 90 days later, evaluations were undertaken. Forty percent of the seedlings presented symptoms, i.e., foliar necrosis and wilt owing to root rot. Fusarium sp. was re-isolated from the affected roots by transferring hyphal tips to potato dextrose agar (PDA) and carnation leaf agar (CLA) medium in petri dishes in order to identify the species morphologically. On PDA, the colony pigmentation was yellowish brown and the aerial mycelium was whitish to peach; macroconidia were relatively long and narrow (31.75 × 4.02 μm), with 5 septa on average, and whip-like bent apical cells (2). Chlamydospores were not observed on PDA or CLA. Primer pairs ITS1 and ITS4 (3) and EF1-T and EF1-1567R (4) were employed to amplify the internal transcribed spacer (ITS) and elongation factor-1α (TEF 1-α) regions, respectively. The resulting DNA sequences showed 99% for ITS and 98% for TEF 1-α similarity with Fusarium equiseti (Corda) Sacc. and phylogenetic analysis grouped it with sequences of this species. The consensus sequence was submitted to GenBank and received the accession numbers KC810063 (ITS) and KF601580 (TEF 1-α). The pathogen was re-isolated on PDA and CLA substrate in order to complete Koch's postulates. The pathogenicity test was repeated with the same conditions described before and the results were confirmed. No symptoms were observed on the control seedlings. This species is considered a weak paras