Abstract
Streptomyces sp. R18(6) and Streptomyces sp. 6(4) strains were evaluated for their ability to control brown spot and common root rot caused by Bipolaris sorokiniana in wheat crops. The antifungal activity of these isolates was tested using a double-layer assay and culture pairing at 28 °C. Physiological and enzymatic activity performed through siderophore, indole-3-acetic acid, nitrogen fixation and phosphate solubilization tests. The biocontrol of the disease and growth-promoting efficiency of wheat seedlings were assessed using in vivo assays in a greenhouse. In the culture pairing assays, both strains inhibited B. sorokiniana mycelial growth, while in the double-layer only Streptomyces sp. R18(6). Streptomyces sp. 6(4) produced auxin, siderophores, fixed nitrogen and solubilized phosphate, whereas R18(6) did not produce siderophores. In the greenhouse assays, strain R18(6) showed statistical differences in shoot dry mass and root dry mass compared with those of strain 6(4) in the presence of the phytopathogen (P ≤ 0.05), and these results were more evident when the environmental temperature was higher. In the absence of the phytopathogen, Streptomyces sp. 6(4) strain increased the root dry mass compared with that of the control during the same period. Therefore, these isolates can potentially control root rot and brown spotting and may promote the growth of wheat plants.
Highlights
Wheat is the second largest cultivated crop in the world (MAPA, 2016) mainly due to its presence in the diets of most nations (BNDES, 2016)
The fungus Cochliobolus sativus is the teleomorph of B. sorokiniana, which is the causal agent of brown spot, seed rot, and common root rot in wheat (Reis, 1988; Rashid et al, 2004; Duveiller et al, 2005)
In the culture pairing assay, the two actinobacterial strains inhibited the radial growth of B. sorokiniana isolate 98004 (Figure 2)
Summary
Wheat is the second largest cultivated crop in the world (MAPA, 2016) mainly due to its presence in the diets of most nations (BNDES, 2016). Wheat is of vital importance to the global agricultural economy The cultivation of this cereal is subject to diseases that compromise its production. The fungus Cochliobolus sativus is the teleomorph of B. sorokiniana (anamorph), which is the causal agent of brown spot, seed rot, and common root rot in wheat (Reis, 1988; Rashid et al, 2004; Duveiller et al, 2005). These diseases cause high losses in the production of this cereal (Reis & Casa, 2005). Bipolaris sorokiniana affects wheat and barley crops in various parts of the world, including Brazil, Canada, Australia, Europe, Asia and Africa (Diehl et al, 1982; Zillinsky, 1984; Stubbs et al, 1986; Reis, 1988; Tinline et al, 1988; Agrios, 1997)
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