First Report of Gray Mold Caused by Botrytis cinerea on Dragon Fruit (Hylocereus undatus) in Mexico.

ABSTRACT

The dragon fruit is native of Mexico, and Puebla is the third-largest producing state (SIAP 2023). In June 2023, field sampling was conducted in El Paraíso, Atlixco (18° 49' 5.275" N, 98° 26' 52.353" W), Puebla, Mexico. The mean temperature and relative humidity were 20 °C and 75% for seven consecutive days. Dragon fruits cv. 'Delight' close to harvest with gray mold symptoms were found in a commercial area of 2 ha, with an incidence of 35 to 40% and an estimated severity of 75% on infected fruit. The symptoms included necrosis at the apex, which later spread throughout the fruit, along with a soft, black rot covered in abundant mycelium and sporulation. The fungus was isolated from 40 symptomatic fruits by disinfesting pieces of necrotic tissue with 3% NaClO for one minute, rinsing with sterile distilled water (SDW), plating on Petri dishes with potato dextrose agar, and incubating at 25 °C in the dark. One isolate was obtained from each diseased fruit by the hyphal-tip method. The colonies were initially white with a growth rate of 1.15-1.32 cm per day and turned gray after 10 days; the mycelium was dense and aerial. Spherical and irregular sclerotia were formed, measuring 0.9-1.4 × 0.6-1.1 mm (n = 100). Each Petri dish produced 56-278 sclerotia (n = 40) after 11 days; these were initially white and gradually turned dark brown. Brown to olive conidiophores were straight, septate, and branched, measuring 1075-1520 × 10-21 µm, with elliptical hyaline to light brown conidia of 6.6-11.5 × 5-8.1 µm (n=100). The isolates were tentatively identified as Botrytis cinerea based on morphological characteristics (Ellis 1971). Two representative isolates were chosen for molecular identification and genomic DNA was extracted by the CTAB protocol. The ITS region and the heat shock protein (HSP60), RNA polymerase binding II (RPB2) and glyceraldehyde 3-phosphate dehydrogenase (G3PDH) genes were sequenced (White et al. 1990; Staats et al. 2005). The sequences of a representative isolate (BcPh5) were deposited in GenBank (ITS-OR582337; HSP60-OR636622; RPB2-OR636623; and G3PDH-OR636621). BLAST analysis of the partial sequences of ITS (479 bp), HSP60 (1006 bp), RPB2 (1126 bp), and G3PDH (907 bp) showed 100% similarity to B. cinerea isolates (GenBank KM840848, MH796663, MK919495, MF480679). Phylogenetic analysis confirmed that BcPh5 clustered with B. cinerea strains. Pathogenicity was confirmed by inoculating the non-wounded surface of 20 detached dragon fruits cv. 'Delight' using the BcPh5 isolate by depositing 20 µl of a 105 conidia/ml suspension with a sterile syringe. The fruits were placed on the rim of a plastic container and inserted in a moisture box with 2 cm of water at the bottom. The box was covered with a plastic sheet to maintain humidity. Control fruits were inoculated with SDW. The inoculated fruits became covered with abundant white to gray mycelium, and soft rot developed within eight days, while no symptoms were observed on the controls. The fungus was re-isolated from the inoculated fruits as described above, fulfilling Koch's postulates. The pathogenicity tests were repeated three times. Gray mold caused by B. cinerea was also recently reported in Mexico on pomegranate (Hernández et al. 2023) and rose apple (Isodoro et al. 2023). As far as we know, this is the first report of B. cinerea causing gray mold on dragon fruit in Mexico. This research is essential for designing integrated management strategies against gray mold on dragon fruits.