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Root and Basal Stem Rot Caused by Gaeumannomyces graminicola on Vetiveria zizanioides in Southern China

Lin, J. M., Liu, J. X., Niu, X. L., Zhang, W.
Plant disease 2019 v.103 no.8 pp. 2128
Chrysopogon zizanioides, DNA primers, Gaeumannomyces, autoclaving, chlorosis, conidia, corn meal, genes, grasses, greenhouses, hyphae, inoculum, leaves, new species, peptide elongation factors, root rot, roots, sand, sandy loam soils, stem rot, stems, subtropics, China
Vetiver grass (Vetiveria zizanioides L.) is a perennial graminaceous plant that is widely used for water and soil protection in tropical and subtropical regions. In September 2016, a root and basal stem rot of V. zizanioides was observed in a field of the Grass Research Station of Lingnan Normal University, Guangdong Province, China. Affected plants had dark brown necrotic lesions with water-soaked margins at stem bases, root rot, leaf chlorosis, and wilt, ultimately followed by collapse of the whole plant. In all cases, a Gaeumannomyces species was consistently isolated from rotted stems and roots on potato dextrose agar. Two pure isolates (ZWGG 411 and ZWGG 413) of Gaeumannomyces sp. were obtained by single-hypha transfers. The colonies of these two isolates were olivaceous gray to dark with funiculose hyphae. Conidia were lunate, slightly or strongly curved, hyaline, 5 to 11.5 × 1 to 2 μm (n = 50). Hyphopodia lobed, brown, 16.5 to 24 × 15.5 to 23.5 μm (n = 50). The morphological characteristics were consistent with those of Gaeumannomyces graminicola M. Hern.-Restr. & Crous, sp. nov. (Hernández-Restrepo et al. 2016). The internal transcribed spacer (ITS) regions as well as the partial translation elongation factor (EF-1α) and large subunit (LSU) genes were sequenced, using primer pairs ITS/ITS4 (White et al. 1990), EF1-983F/EF-1567 (Rehner and Buckley 2005), and LR5/LR0R (Vilgalys and Hester 1990), respectively. The obtained sequences were deposited in GenBank under the following accession numbers: ITS, MK045729 and MK045730; EF-1α, MK053817 and MK053818; and LSU, MK045731 and MK045732. BLASTn searches showed 98 to 99% identity with the existing sequences of ex-type isolate CBS 352.93 of G. graminicola (accession nos.: ITS, KM484834; EF-1α, KX306697; and LSU, DQ341496). Koch’s postulates were confirmed on 6-week-old V. zizanioides in 10-cm-diameter pots containing sandy loam soil. Inoculum was prepared by incubating autoclaved sand and corn meal (150 g of sand and 50 g of corn meal) with the two isolates for 4 weeks at 25°C. Ten grams of inoculum were buried 1 cm deep approximately 2 cm from the base of the plant in each of the six pots as six replications, and plants in pots inoculated with sterilized sand and corn meal served as controls. Plants were kept in a greenhouse at 28 ± 2°C and watered to soil saturation once a week. Inoculated plants developed symptoms of root and basal stem rot after 4 weeks and wilted within 8 weeks after inoculation. Control plants remained healthy. G. graminicola was consistently reisolated from inoculated plants. To our knowledge, this is the first report of G. graminicola causing root and basal stem rot of V. zizanioides in China and worldwide.