In May 2019, sugar beet (Beta vulgaris L.) seedlings were observed
with stunted growth, yellowing of leaves, and dying seedling root tip
tissue discoloration in Sidney (47.7167° N, 104.1563° W), Montana.
The disease affected about 40% of the 10 ha commercial field. Roots
of infected seedlings were surface sterilized with 70% ethanol for 30
seconds, rinsed with sterile distilled water and cultured on amended
50% potato dextrose agar (PDA) for 7 days at 25°C. The isolated
fungus produced white to yellow aerial mycelium. Macroconidia
(18.9 to 30.3×2.5 to 3.6 µm, 5-7 septate) exhibited dorsoventrally
curvature. No microconidia were found. Chains of chlamydospores
were observed in three weeks old cult... More
In May 2019, sugar beet (Beta vulgaris L.) seedlings were observed
with stunted growth, yellowing of leaves, and dying seedling root tip
tissue discoloration in Sidney (47.7167° N, 104.1563° W), Montana.
The disease affected about 40% of the 10 ha commercial field. Roots
of infected seedlings were surface sterilized with 70% ethanol for 30
seconds, rinsed with sterile distilled water and cultured on amended
50% potato dextrose agar (PDA) for 7 days at 25°C. The isolated
fungus produced white to yellow aerial mycelium. Macroconidia
(18.9 to 30.3×2.5 to 3.6 µm, 5-7 septate) exhibited dorsoventrally
curvature. No microconidia were found. Chains of chlamydospores
were observed in three weeks old culture. The morphological features
of the isolates were consistent with Fusarium equiseti [1,2]. Genomic
DNAs (NORGEN BIOTEK CORP, Fungi DNA Isolation Kit #26200)
of three representative isolates were used for polymerase chain
reaction (PCR) with the internal transcribed primers (ITS1-ITS4) [3].
The amplified PCR products were cleaned by E.Z.N.A ®Cycle Pure
Kit, OMEGA and the three samples were sent for Sanger sequencing
to GenScript (GenScript, Piscataway, NJ). Nucleotide Blast analysis
showed 100% sequence alignment to Fusarium equiseti with GenBank
accessions MN049482.1, MN049480.1, MK990145.1, MK764999.1,
MK770797.1, MK962344.1, MK990137.1, and MK990143.1. The
sequence was submitted to GenBank with accession no. MN128568.
Pathogenicity testing was done using 10, 2-week old sugar beet
seedlings (Hilleshog proprietary material) grown individually in
pots (4˝×4˝×6˝). Seedlings were inoculated (conidial suspension,
104
conidia/ml for 8 minutes) by the root dip method [4]. Mock
inoculated plants were dipped in sterile water. Inoculated and control
plants were placed in the greenhouse at 25 ± 2°C, and 75% to 85%
relative humidity. Two weeks later, all inoculated seedlings showed
symptoms similar to those observed in the field and non-inoculated
seedlings were symptomless. This study was repeated. The fungus was
isolated from diseased roots and confirmed to be Fusarium equiseti
based on morphological characters. Fusarium equiseti was reported in freshly harvested and stored sugar beet in Europe; however, it was not
found to be pathogenic [5,6]. reported that F. equiseti was associated
with root rot of sugar beet but did not report pathogenicity. This
pathogen is reported in several crops including edible beans which
is grown as a rotational crop with sugar beet in several production
areas [7]. The most important Fusarium species reported to cause
significant economic damage to sugar beet include F. oxysporum and
F. secorum [8,9]. The presence of another pathogenic Fusarium species
in sugar beet will require monitoring to determine how widespread
it is and whether current commercial cultivars are resistant. To our
knowledge, this is the first report of Fusarium equiseti causing disease
on sugar beet seedlings in the USA.
