Characterization of Fusarium species causing dry root rot disease of citrus trees in Morocco

Citrus have been grown as a commercial fruit crop in Morocco for a decade. The area dedicated to growing and producing citrus has increased from 2006 to 2018 throughout the country. The rapid decline of citrus trees has been observed in many locations. Therefore, this study aimed to identify and characterize fungal pathogens associated with dry root rot (DRR) disease of citrus from diseased trees and soil collected from different citrus-growing plantations. Isolation and morphological identification of pathogens were performed using PDA-SC medium. Thirty-four Fusarium isolates were recovered from symptomatic plants. These isolates were identified based on morphological traits and the sequence of the internal transcribed spacer (ITS) region. Four Fusarium species were identified. Fusarium solani (Martius) was most frequently identified (70.60%), followed by F. oxysporum (17.65%), F. equiseti (8.82%) and F. brachygibbosum (2.94%). The two latter species have recently been associated with DRR in Morocco. Two separate pathogenicity trials were conducted to test the effect of the pathogens on young citrus seedlings. Results indicated that, with the exception of F. equiesti, Fusarium isolates were aggressive pathogens of citrange-Troyer and sour orange seedlings 2 months postinoculation. Citrus trees displayed key symptoms of DRR such as root rot, discolored and necrotic roots, purple wood discoloration, plant yellowing and general weakness. Further, all four species were able to induce lesions when they were used to inoculate citrus branches. This is the first detailed report of Fusarium species associated with DRR in Morocco.