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First Report of Fusarium globosum Associated with Barley Grain in the Southwestern Part of Siberia

Gagkaeva, T. Y., Gavrilova, O. P., Orina, A. S.
Plant disease 2019 v.103 no.3 pp. 588
DNA, Fusarium fujikuroi, Hordeum vulgare, agar, antibiotics, barley, benzimidazole, chlamydospores, chlorosis, conidia, corn, culms, cultivars, fumonisins, fungi, genes, leaves, mycelium, mycobiota, necrosis, octoxynol, pathogenicity, pathogens, pigmentation, plant tissues, potatoes, sodium hypochlorite, soil, sporodochia, sporulation, sucrose, wheat, Japan, Siberia, South Africa
In 2017, wheat and barley grain samples from the Siberian region were surface sterilized using 3% NaOCl and cultured on 1.5% potato sucrose agar (PSA), amended with antibiotic solutions and Triton X-100. Then the Petri dishes were incubated in darkness for 7 days at 25°C. In addition to other fungi common to grain mycobiota of this region, in one sample of malting spring barley (Hordeum vulgare L.) cultivar Quench, Novosibirskaya Oblast, Russia (53°87′N, 79°32′E) among the 280 analyzed grains three violet-colored colonies of Fusarium were detected. The cultural and morphological characteristics of these Fusarium isolates were suggestive of F. globosum Rheeder, Marasas & P.E. Nelson belonging to the F. fujikuroi species complex (Rheeder et al. 1996). Single-spore cultures of these colonies were identified by morphological characteristics. In the dark, the isolates on PSA produced white to violet aerial mycelium and pigmentation usually with purple or violet tinges. Sporulation began quickly on the aerial mycelium on monophialidic and polyphialidic conidiogenous cells bearing two microconidial types: clavate to ellipsoidal (3 to 15 × 2 to 4 µm) in false heads and in chains, and abundant globose hyaline conidia (10 to 15 µm) produced singly or in botryose cluster. A few fusiform and falcate macroconidia on aerial mycelium were detected (22 to 65 × 3 to 4 µm). Sporodochia and chlamydospores were absent. To confirm the morphological identification, genomic DNA was extracted from the isolates, and the translation elongation factor-1α gene was sequenced (O’Donnell et al. 1998). The obtained sequences (GenBank accession nos. MH446372 and MH446373) were identical to each other and had 98% identity with the homologous site of F. globosum ex-type strain CBS 430.97. Both isolates were tested for pathogenicity on detached leaves of wheat cultivar Bezostaya 100 and plants of maize cultivar ROSS 272, which had previously been wounded with a sterile needle. Ten leaves of wheat (7 days old) were inoculated with PSA disks (3-mm diameter) from F. globosum cultures and placed on a filter disk moistened with 0.004% benzimidazole water solution in Petri dishes. Three maize plants (10 days old) grown in one pot with soil were inoculated with PSA disks (3 mm) that were placed on the stem above the first leaf sheath. Plants were incubated under conditions with 12 h of light per day at 25°C. In a control, pure disks of PSA were used. After 7 days, chlorosis and necrosis were observed on inoculated wheat leaves and maize stems, whereas the control plants remained symptom-free. Koch’s postulates were fulfilled successfully, because the pathogen was reisolated from symptomatic plant tissue after surface sterilization and subsequent incubation on PSA. To date, there are only two reports on the detection of F. globosum. This fungus was previously isolated from maize grain samples in South Africa (Rheeder et al. 1996) and subsequently from wheat culms in subtropical Japan (Aoki and Nirenberg 1999). This first discovery of F. globosum in Siberia is worthy of note, because this species is currently known previously only from warmer environments. F. globosum is known to be a fumonisin producer (Moses et al. 2010), and that is why one might be concerned about its presence in grain.