Characterization of plant-associated microorganisms with beneficial effects on wheat growth

Abstract

The environmental impact of conventional agricultural practices has led to an urgent need of finding alternative solutions for improving agriculture sustainability. In particular, wheat is one of the most important crops in the agro-food sector. Tetraploid wheat production has an important role in Italy where is cultivated mainly in the southern regions, including Sicily. Recently, there was a rising interest in the valorization of local ancient wheat landraces as an important source of genetic and microbial diversity. To date, the study of the plant microbiota has become particularly important due to its influence on plant physiology and health condition. Indeed, promising results have been obtained so far in the field using manipulated microbiota, allowing the formulation of biofertilizers and biocontrol products that can contribute in lowering the effects of agricultural systems on the environment and human health. In addition, insect pests are responsible for significant yield losses in many important crops, causing both direct damages to the plant and by transmitting plant viruses. In particular, the cereal-feeding aphids Rhopalosiphum padi and Sitobion avenae can carry multiple plant viruses and inhibit plant growth on many cereal crops, including wheat. Presently, the principal method adopted to reduce crop damage caused by aphids is insecticide use, which has negative environmental impact and risks development of insecticide resistance. Plant growth promoting rhizobacteria (PGPR) and several fungal genera are widely studied for their ability of promoting plant growth through several mechanisms, including increasing soil nutrient availability and biocontrol activities. The plant microbiota can also influence plant responses to insect pests. Furthermore, the study of endophytes could be of particular interest for their ability of establishing a mutualistic interaction with the plant. In this framework, the study of beneficial microorganisms is of particular interest as it could allow the development of new bioformulations to improve agriculture sustainability. Recently, technologies based on spectral data acquisition, including proximal and remote sensing, are acquiring great importance in agriculture for the possibility of measuring parameters associated to plant physiology and health through hyperspectral vegetation indices (HVIs). For this reason, these approaches found broad application in the field of precision agriculture for it does not require destructive sampling and it can provide useful information that might enhance decision making and a more efficient use of agricultural inputs in specific areas within the field. However, the relationship between hyperspectral data acquired through proximal sensing technology and the composition of plant microbiota or beneficial microbial activities associated to the plant is still poorly understood. Therefore, the objectives of the present study were: to explore the composition of the microbial community associated to two ancient tetraploid wheat landraces native of the Sicilian territory, Perciasacchi (winter wheat) and Tumminia (spring wheat); to identify wheat-associated HVIs related to plant growth and the presence of beneficial strains or microbial activities. To achieve these goals, a multidisciplinary approach was used involving plate-culturing methods, hyperspectral vegetation index measures through proximal sensing technology, high-throughput sequencing analyses and glasshouse experiments. These approaches allowed to expand our knowledge about the composition of the endophytic fungal community associated to ancient wheat cultivars. In addition, a group of potential PGPR strains isolated from field-grown plants was selected based on their in vitro activities and 16S ribosomal sequence data. The effects of the selected PGPR isolates on plant growth and susceptibility to aphid pests were also evaluated on modern and ancient wheat varieties. Finally, HVIs related to the occurrence of some endophytic fungal genera and to beneficial bacterial activities were also identified.