Impact of long-term application of paclobutrazol in communities of arbuscular mycorrhizal fungi and their efficiency in the development of Helianthus annuus L.

Abstract

Paclobutrazol (PBZ) is a phytoregulator known for inhibiting plant vegetative growth and promoting flowering in mango crop (Mangifera indica L.). PBZ belongs to the triazole family, a group recognized by its fungicide capacity, and its application to the soil can directly influence microbial communities, however, little is known about its effects on arbuscular mycorrhizal fungi (AMF). The objectives of this work were to evaluate the impact of long-term application of PBZ on the AMF communities and to verify whether the management time affects the functionality of these communities in promoting the development of ornamental sunflower Helianthus annuus L. (var. Dwarf Double Sungold). Sampling was carried out in mango cultivation areas with a history of PBZ application that varied from no application to application for up to 15 years. For the analysis of the AMF community, the quantification of most probable number (MPN) of infective AMF propagules, abundance of glomerospores, richness, diversity, Simpson dominance, and Pielou's evenness were evaluated. The analysis of the functionality of the AMF community was based on the analysis of the variables of growth and mycorrhizal colonization. Soils with a prolonged history of PBZ application (>nine years) presented distinct AMF communities with lower abundance of glomerospores in relation to areas without PBZ application and with native Caatinga vegetation. However, the soil-inoculum of this AMF community has greater efficiency in promoting sunflower development and mycorrhizal colonization, suggesting greater functionality. It is concluded that the time of application and performance of PBZ in the soil influence the composition of the AMF community. Even with reduction of richness and diversity of AMF species in soils with a prolonged history of PBZ application, there are functional AMF communities in these soils that promoted sunflower plant growth, selecting more efficient and resistant species.