Effect of seed treatment duration on growth and colonization of Vicia faba by endophytic Beauveria bassiana and Metarhizium brunneum

•Seeds inoculated with B. bassiana and M. brunneum for 2, 8, or 16 h.•Several plant growth parameters sampled 7, 14, and 28 days post inoculation.•Evidence that both endophytic fungi can also act as plant growth promotors.•First report for the effect of increased seed treatment duration on plant growth.

The effect of increased duration of seed treatment with two fungal entomopathogens, Beauveria bassiana (NATURALIS) and Metarhizium brunneum (BIPESCO5), on the growth and colonization of broad bean (Vicia faba) was assessed in two replicate greenhouse experiments. The plants were inoculated by soaking seeds in a concentration of 1 × 107 conidia ml−1 of each of the two fungal strains or in sterile distilled water containing 0.1% Tween 80 for 2, 8, and 16 h. Percent seed germination and seedling emergence as well as primary root length were determined seven days post inoculation. Effects of fungal strain and seed treatment duration on plant height, number of leaf pair, fresh root and shoot weight were measured 14 and 28 days post inoculation. Seed treatment with either fungal strain significantly enhanced almost all measured plant growth parameters. Overall, plant growth was also significantly enhanced as seed treatment duration increased; irrespective of fungal strain. Percent colonization of different plant parts (root, leaf, and stem) sampled 14 and 28 days post inoculation increased as the duration of seed treatment increased as well. The increase in colonization rate due to increased seed treatment duration varied significantly among plant parts, but not among both sampling dates. Our study demonstrates that M. brunneum can systemically colonize different plant parts and improve plant growth when applied as a seed treatment. This was also confirmed for the well-known endophytic B. bassiana strain used in this study. Our results also provide the first report for the effect of increased duration of seed treatment with both endophytic fungal entomopathogens on plant growth enhancement.

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