Molecular identification of some plant growth promoting microorganisms and their evaluation on growth characteristic of wheat

Wheat is one of the most important food crops. In modern agriculture, Due to the increasing human population and the detrimental effects of chemical fertilizer such as environmental pollution and concerns about human health, adapting suitable alternatives like production of bio-fertilizers which have none of these dangerous effects would be necessary. Plant growth-promoting fungi and bacteria used in bio-fertilizers are the beneficial microorganisms that can enhance plant growth, yield and resistance to biotic and abiotic stresses directly or indirectly through a wide variety of mechanisms. Although bio-fertilizers have become more noticeable in recent years, the lack of accurate identification of microorganisms used in the production of these fertilizers is one of the problems of bio-fertilizers in Iran. Failure to accurate identification of species is due to deficiencies in morphological or biochemical methods in fungi and bacteria. Therefore, the purpose of this study was to identify of fungal and bacterial isolates molecularly and also to investigate the effect of these isolates alone and in combination with arbuscular mycorrhizal fungus on some growth characteristics of the wheat plant.

After the preparation of fungal and bacterial isolates from the Soil and Water Research Institute, which are known as plant growth promoting microorganisms, accurate identification of each isolate was performed based on morphological and molecular methods. Extraction of genomic DNA in arbuscular mycorrhizal fungus was done by single-spore method and in other bacterial and fungal isolates by CTAB method. Amplification of 16S rDNA region in bacterial isolates, TEF-1α and ITS1-5.8S-ITS2 regions in Trichoderma species, ITS1-5.8S-ITS2 region in Serendipita indica and SSU-ITS1-5.8S-ITS2- LSU region by nested PCR method in the arbuscular mycorrhizal fungus was performed. To investigate the effect of fungal and bacterial isolates alone or in combination with arbuscular mycorrhizal fungus in a greenhouse, their effect on wheat growth indices such as plant height, shoot and root dry weight, head height and weight and dry weights of seeds were measured.

Based on morphological and molecular investigation, three species of Bacillus including Bacillus velezensis, B. pumilus, and B. subtilis and three species of Trichoderma including Trichoderma atroviride, T. longibrachiatum, and T. harzianum and S. indica and Rhizophagus irregularis were identified. T. harzianum + R. irregularis and T. longibrachiatum showed the maximum dry weight and head weight. T. longibrachiatum + R. irregularis and T. atroviride showed the highest effect on plant height. Pots treated with T. harzianum + R. irregularis, T. harzianum, T. atroviride, and S. indica+ R. irregularis showed the highest weight of seeds compared to control plants.

The result showed that the effect of fungal treatments such as T. harzianum + R. irregularis and Trichoderma spp. on growth characteristics of wheat was significant. According to the results of this study, the use of an appropriate combination of inoculants and the preparation of primary formulations for use in farm experiments is proposed to increase the availability of nutrients and improve the growth of wheat plants. Keywords: Arbuscular mycorrhizal fungus, Bacillus, Plant growth promoting fungi, Trichoderma