Characterization of Fusarium solani associated with tobacco ( Nicotiana tabacum L.) root rot in Henan, China.

The aim of this study was to characterize the Fusarium solani species complex (FSSC) population obtained from tobacco roots with root rot symptoms using morphological characteristics, molecular tests, and assessment of pathogenicity. Cultures isolated from roots were white to cream with sparse mycelium on PDA with colony growth of 21.5 ± 0.5 to 29.5 ± 0.5 mm after 3 days. Sporodochia were cream on carnation leaf agar (CLA) and spezieller nährstoffarmer agar (SNA), and macroconidia formed in sporodochia were 3- to 6-septate, straight to slightly curved, with wide central cells, a slightly short blunt apical cell, and a straight to almost cylindrical basal cell with a distinct foot shape, ranging in size from 20.92 to 64.37 μm × 3.91 to 6.57 μm. Microconidia formed on CLA were reniform and fusiform with 0 or 1 to occasionally 2 septa, that formed on long monophialidic conidiogenous cells, with a size range of 5.99 to 32.32 μm × 1.76 to 5.84 μm. Globose to oval chlamydospores were smooth to rough-walled, 6.5 to 13.3 ± 0.37 μm in diameter, terminal or intercalary, single or in pairs, occasionally in short chains on SNA. Molecular tests consisted of sequencing and phylogenetic analysis of the translation elongation factor-1 alpha ( EF-1α ), RNA polymerase II largest subunit ( RPB1 ), and second largest subunit ( RPB2 ) regions. All the obtained sequences revealed 98.14%~100% identity to Fusarium solani in both Fusarium ID and Fusarium MLST databases. Phylogenetic trees of the EF-1α gene and concatenated three-loci data showed that isolates from tobacco in Henan grouped in the proposed group 5, which is nested within FSSC clade 3 (FSSC 5). Twenty-seven of the 28 isolates caused a root rot of artificially inoculated tobacco seedlings, with a disease index ranging from 15.00 ± 1.67 to 91.11 ± 2.22. Cross pathogenicity tests showed that three representative isolates were virulent to six species of Solanaceae and two of Poaceae , with disease indexes ranging from 6.12 ± 0.56 to 84.44 ± 0.00, indicating that these isolates have a wide host range. The results may inform control of tobacco root rot through improved crop rotations.