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

Antonina Sorokan,Svetlana Veselova,Igor Maksimov,Galina Benkovskaya

doi:10.3390/plants10050923

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.

Highlights

Damage caused by pathogens and insect pests is among the most important factors that reduce the productivity of agricultural plants
We demonstrated the significant decrease of growth of plant shoots that was accompanied by the decrease of indole-3-acetic acid (IAA), abscisic acid (ABA) and cytokinins level and, the importance of the ability of B. subtilis 26D to maintain phytohormones levels in plants and to promote plants’ adaptation to Colorado potato beetle (CPB)-caused damage
On shoots parameters and the levels of IAA, ABA and zeatin was significant only when plants were affected by CPBs, and the impact of this phytohormone-producing strain cannot deform the phytohormonal status of plants under the normal conditions

Summary

Introduction

Damage caused by pathogens and insect pests is among the most important factors that reduce the productivity of agricultural plants. In the majority of plant species, the activation of defense systems leads to interruption of growth—this effect is commonly known as the growth–defense trade-off [2]. While mechanisms of plant defense against pest insects have been extensively investigated, little attention has been paid to the mechanisms of restoring the growth characteristics of plants after damage caused by defoliators, this is the most important condition for the formation of stable yields. The Colorado potato beetle (CPB) Leptinotarsa decemlineata Say (Coleoptera, Chrysomelidae) is harmful and adaptive to changing environmental factors, a defoliating insect known as an aggressive invader and for its capacity to rapidly develop resistance to insecticides [1]

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