First Report of Gilbertella persicaria Causing Soft Rot in Eggplant Fruit in Brazil

In March 2017, two eggplant fruit (Solanum melongena cv. Ciça) were collected from field production in Chã-Grande, in the state of Pernambuco, Brazil, with circular, light brown and slightly sunken lesions in the apex, extending to the entire fruit in 3 to 4 days and developing a soft rot with abundant mycelial and sporangia production on the surface. After microscopic examination, a fungus belonging to the genus Gilbertella was identified. The fungus was isolated from soft rot observed in the fruit and pure cultures were obtained by transferring a single spore to potato dextrose agar (PDA). Two isolates were obtained and deposited in the culture collection “Micoteca URM Profa. Maria Auxiliadora Cavalcanti” at the Universidade Federal de Pernambuco (Recife, Brazil), as URM7670 and URM7671. Morphological characteristics include spherical, single sporangia with 57.2 to 96.2 µm diameter, yellow-brown to brown when young turning dark brown or black on maturity, and sporangia split longitudinally into two halves to release the spore and expose a columella obvoid, 23.4 to 65 × 26 to 52 µm. The sporangiospores were mostly globose to ellipsoid, smooth, hyaline, aseptate, and 7.8 to 13 × 5.2 to 10.4 µm. The morphological characteristics evaluated corroborate previously published data for Gilbertella persicaria (Benny 1991). The partial sequences of the internal transcribed spacer (ITS) and 28S (LSU) of the rDNA were obtained for the two isolates and deposited in GenBank (accession nos. MF804516, MF804517, MG573061, and MG573062, respectively). The isolates showed a 99% similarity with ITS and LSU sequences of the type strain G. persicaria CBS 190.32 (NR111692 and JN939197, respectively) according to BLAST search. A combined phylogenetic tree obtained by Bayesian method grouped the isolates with the G. persicaria clade with 100% of posterior probability, confirming the identification. Koch’s postulates were conducted by inoculating five asymptomatic eggplant fruit (cv. Ciça) previously disinfested with 0.5% hypochlorite and unwounded or superficially wounded with a sterile needle at two equidistant points. Ten milliliters of a sporangiospore suspension (1 × 10⁵ sporangiospores/ml) obtained from a representative isolate (URM7670) were sprayed on the inoculation sites. Sterile distilled water was used as control. The inoculated fruits were maintained in plastic boxes that contained a portion of moistened cotton wool and were maintained in a moist chamber at ∼25°C for 5 days. Wounded inoculated fruit showed the first symptoms (circular, light brown spots) 48 h after inoculation and evolved into soft rot after 5 days. Hyaline hyphae and light brown to dark sporangia were observed over the surface of the infected fruit. The pathogen was reisolated, fulfilling Koch’s postulates. The control and unwounded fruit remained asymptomatic. This species is usually found in soils and dung, but has already been reported to cause rot in peach fruit (Ginting et al. 1996), dragon fruit (Guo et al. 2012), black plum (Pinho et al. 2014), and papaya (Cruz-Lachica et al. 2016). To our knowledge, G. persicaria represents a new report in the world associated with soft rot in eggplant. This work will certainly contribute to the knowledge of pathogens that affect eggplant culture and, consequently, future studies that involve disease management strategies.