First report of Thielaviopsis ethacetica causing black rot in Bactris gasipaes fruit in Brazil.

The peach palm (Bactris gasipaes Kunth) is a palm of great importance to the population of the Brazilian Amazon region. Its fruits are an important food source for the local population (Alves and Flores, 1982). Between 2018 and 2021, peach palm fruits with black rot symptoms were collected in the state of Pará, in the municipalities of Juruti (02 09' 08'' S 56 05' 32W) and Santarém (2 26' 22''S 54 41' 55''W), Brazil. Symptomatic fruits detach easily from the bunch. When sectioned, tissues with black coloration and mycelia with white to black coloration were found (Fig. 1a-b). The incidence of the disease in orchards ranged from 5 to 50%. Then, direct isolation, was done by transferring fragments of mycelia and spores to a plate containing potato dextrose agar (PDA). Morphological markers of the asexual phase were evaluated by cultivating the isolates in malt extract agar (MEA) with fragments of Saccharum officinarum culm (Mbenoun et al., 2014). The colonies initially showed a white coloration but turned dark after eight days of cultivation. Colonies produced white mycelia with hyaline, unicellular, rectangular primary conidia (5.6-8.8 µm) (n=30) in length and 2.8-4.0 µm (n=30) in width (Fig. 1e). In the dark-colored mycelia, secondary conidia that formed exhibited three distinct shapes: cylindrical, light brown, and (6.6-11.6 µm x 3.0-3.7 µm) (n=30) (Fig 1. f-i); oblong to globose shape (5.0-10.0 x 3.0-5.3 µm) (n=30) (Fig 1. g); and ellipsoid-shaped (7.0-13.0 x 3.0-4.0 µm) (n=30) (Fig 1. h). Furthermore, unicellular aleuroconidia, produced in dark-colored colonies, exhibited cell walls (10.8-17.5 x 5.4-8.4 µm) (n=30) with a warty, dark-brown, ovoid-shaped appearance (Fig 1. j-k). Genomic DNA was isolated from 4-day-old cultures, and ITS-rDNA and TEF-1α were amplified from ITS1/ ITS2 (White et al., 1990) and EF1F/EF2R (Jacobs et al., 2004), respectively. Sequences were deposited in GenBank (ITS: OL623838, OL623839, OM643316, OL623840, and OL623841) (TEF1: OL631623, OM643318, OM643317, OL631624, and OL631625). Bayesian analysis concatenated were conducted with MrBayes v. 3.2.7 (Ronquist et al., 2011). Clustered the five isolates with the Thielaviopsis ethacetica reference isolate IMI 50560 with Bayesian posterior probability (Bpp = 0.99). (Fig. 2). The pathogenicity test, was conducted using the five isolates, that were were inoculated on six fruits early maturity. After the fruit were washed with neutral detergent and water, 0.5-cm-deep wounds were made with a sterile penknife. Next, 1 mL of primary and secondary conidia suspension at 1 x 105 spores/mL was added to each wound. Six control fruit were inoculated with distilled water. The fruits were kept in incubators at 25 °C with a 12 h photoperiod. The experiment was conducted twice (Alves and Flores, 1982). After five days of inoculation, all inoculated fruit showed characteristic symptoms (Fig 1. c), whereas the control fruit remained asymptomatic (Fig 1. d). The fungus reisolated from all inoculated fruit exhibited the same morphological markers as the inoculated fungus, thus completing Koch's postulates. Thielaviopsis ethacetica is an important pathogen in several palm species in sugarcane and pineapple crops in different parts of the world (Mbenoun et al., 2014; Borgens et al., 2019). This study is the first record of T. ethacetica causing black rot in B. gasipaes fruit in Brazil.