Characterization and pathogenicity of Fusarium species causing sugar beet root rot in Morocco

The sugar beet crop ranks second globally among the plant species grown mainly for sugar production. In Morocco, the area under sugar beet farming occupies approximately 57,000 ha yielding more than 3 million tons of roots. However, sugar beet root-tip rot (RTR) caused by Fusarium spp. dramatically reduces the anticipated yields, the purity of the resulting juice, and the sugar concentration. The current study aimed at identifying and characterizing the Fusarium species responsible for the root rot in sugar beet grown in the Khenifra-Beni Mellal region of Morocco. In this survey, 69 isolates of Fusarium were sampled from sugar beet roots showing typical symptoms of root rot from 2019 to 2021. After screening based on the pathogenicity test, 28 isolates were selected and identified based on morphological features and sequence analyses of the ribosomal internal transcribed spacer (ITS) region and translation elongation factor 1 a 34 (TEF-1 a). Fusarium oxysporum was the most frequently identified species, followed closely by F. solani, F. equiseti, F. nygmai, F. brachygibbosum, F. proliferatum, F. culmorum, and F. falciforme. Six weeks after inoculations under greenhouse conditions, the studied isolates caused internal vascular discoloration and tip rot of sugar beet roots, with disease incidences ranging from 37.5% to 100.0% and a disease index between 30.3% and 70.5%. Isolates belonging to F. solani were the most aggressive. Moreover, the majority of isolates significantly reduced plant growth. To our knowledge, this research article is the first report of Fusarium species inducing RTR in sugar beet in Morocco.