Endophytic Strain Bacillus subtilis 26D Increases Levels of Phytohormones and Repairs Growth of Potato Plants after Colorado Potato Beetle Damage

Abstract

Plant damage caused by defoliating insects has a long-term negative effect on plant growth and productivity. Consequently, the restoration of plant growth after exposure to pathogens or pests is the main indicator of the effectiveness of the implemented defense reactions. A short-term Leptinotarsa decemlineata Say attack on potato tube-grown plantlets (Solanum tuberosum L.) led to a reduction of both the length and mass of the shoots in 9 days. The decrease of the content of phytohormones-indole-3-acetic acid (IAA), abscisic acid (ABA), zeatin and zeatin-riboside-in shoots of damaged potato plants was found. Endophytic strain Bacillus subtilis 26D (Cohn) is capable of secreting up to 83.6 ng/mL IAA and up to 150 ng/mL cytokinins into the culture medium. Inoculation of potato plants with cells of the B. subtilis 26D increases zeatin-riboside content in shoots and the mass of roots of undamaged plants, but does not influence content of IAA and ABA and growth of shoots. The presence of B. subtilis 26D in plant tissues promoted a rapid recovery of the growth rates of shoots, as well as the wet and dry mass of roots of plants after the pest attack, which we associate with the maintenance of a high level of IAA, ABA and cytokinins in their tissues.

Keywords: Bacillus subtilis; Leptinotarsa decemlineata; Solanum tuberosum; abscisic acid; endophyte; indole-3-acetic acid; zeatin; zeatin–riboside.

Figure 1

Influence of damage caused by CPB on the length of shoots (A) and the growth addition of shoots (B) of potato plants treated with water or suspension of B. subtilis 26D. The values are means, and the vertical bars represent standard errors. Data analyzed using two-way ANOVA with Tukey’s post hoc test. Asterisks indicate means statistically different from the control at p ≤ 0.05. CPB—plants damaged by Colorado potato beetle.

Figure 2

Influence of B. subtilis 26D on fresh (A) and dry (B) weights of shoots and roots of potato plants on the 9th day post damage caused by CPBs. The values are means, and the vertical bars represent standard errors. Data analyzed using two-way ANOVA with Tukey’s post hoc test. Asterisks indicate means statistically different from the control at p ≤ 0.05. c—control plants (water-treated intact plants); CPB—plants damaged by Colorado potato beetle.

Figure 3

Influence of B. subtilis 26D on the level of IAA (A) and ABA (B) in potato plants on the 1st, 2nd and 3rd day after damage caused by CPBs. The values are means, and the vertical bars represent standard errors. Data analyzed using two-way ANOVA with Tukey’s post hoc test. Asterisks indicate means statistically different from the control at p ≤ 0.05. c—control plants (water-treated intact plants); CPB—plants damaged by Colorado potato beetle.

Figure 4

Influence of B. subtilis 26D on the level of zeatin (A) and zeatin–riboside (B) in potato plants on the 1st, 2nd and 3rd day after damage caused by CPBs. The values are means, and the vertical bars represent standard errors. Data analyzed using two-way ANOVA with Tukey’s post hoc test. Asterisks indicate means statistically different from the control at p ≤ 0.05. c—control plants (water-treated intact plants); CPB—plants damaged by Colorado potato beetle.