Changes in the morphology of the root system of wheat inoculated with Azospirillum brasilense Sp7 and bacteriophage FAb-Sp7

The Azospirillum is one of the most common objects to study associative interactions between bacteria and plants. In the rhizosphere of cereals the Azospirillum cells form effective association and demonstrate a stimulating effect on plant growth and development, in particular in wheat. However, the details of these positive effects are still unknown. For example, there is no evidence of whether the Azospirillum cells are infected with bacteriophages, and little is known about the role that the bacteriohages of soil microorganisms can play in the development of associative relationship between microorganisms and plants. Nevertheless, the bacteriophages are well known to control the bacteria number in the population and be involved in genetic transduction. Note that the studied bacteriophages are mostly isolated from environment, in particular, from soil, while the bacteriphages of associative soil bacteria still remain poorly studied. To evaluated changes in the morphology of the wheat ( Triticum aestivum L.) root system in Saratovskaya 29 variety after inoculation with Azospirillum brasilense Sp7 bacterial cells and bacteriophage FAb-Sp7, isolated from these cells, we first inoculated the 3-day old wheat seedlings with A. brasilense Sp7 at 10 8, 10 6, 10 4 cells per 1 ml. It resulted in a decrease in the length of the root, and the number of lateral roots grew considerably at 10 2 cells per 1 ml. After treatment wiht bacteriophage FAb-Sp7 an average number of roots remained unchanged. It was shown that wheat seedling inoculation with Azospirillum suspension resulted in a 3-fold decrease in root elongation zone, and the suction zone reduced 1.5 times. Treatment of wheat seedlings with a suspension containing Azospirillum and phages resulted in a 3.3-fold decrease in the tensile zone, but the root hair zone remained unchanged. Using confocal microscopy we demonstrated that incubation of wheat seedlings with Azospirillum at 10 2 cells per 1 ml significantly increased the number and length of root hairs (on average by 40 %) compared with the control. It was shown that a simultaneous inoculation with Azospirillum Sp7 cells and bacteriophage FAb-Sp7 also increased the number and length of root hairs (60 % on average) compared with control. It is suggested that bacteriophages of Azospirillum are involved into complex interaction of bacteria with wheat root system, and can influence on and, ultimately, determine the effectiveness of associative relationships between the plant and microorganisms.