Microbiota do solo em três sistemas de cultivo de citros e patogenicidade de Fusarium spp.

Abstract

Different production systems utilize management techniques that seek to supply nutritional needs, together with the control of pests and diseases that are harmful to plants. However, some of these techniques can be harmful to microorganisms and, mainly, to those present in the soil microbiota, since some of them have pathogenic ad others antagonistic potential. It is very important to understand the ecology of microorganisms present in different farming systems, searching for a production system less prejudicial to the environment. The objectives of this paper were: to identify and quantify the fungal population in three citrus cultivation systems (organic, agroforestry and conventional managements); to evaluate the pathogenicity of Fusarium spp. isolates to Citrus deliciosa Tenore seedlings; and to evaluate the antagonistic potential of Trichoderma spp. isolates in relation to Fusarium spp. isolates. Soil samples were collected in Montenegro, RS, Brazil, in citrus orchards with different managements, at 0-5 cm depth in the summer and winter of 2015 and 2016. Fungal population (through serial dilutions) and physical and chemical characteristics of the soil were evaluated. Fungi of genus Fusarium and Trichoderma were isolated for further morphological characterization and molecular identification (based on TEF-1α region). In vitro tests (direct confrontation) were performed to evaluate the control efficiency of Fusarium spp. by Trichoderma spp. The chemical characteristics and the fungal populations showed significant correlations, which are favored by the management system. The Fusarium species identified were: F. solani, F. oxysporum, and F. oxysporum f. sp. vasinfectum and of Trichoderma were: T. asperellum, T. harzianum, and T. koningiopsis. The Trichoderma spp. isolates have good ability to inhibit the in vitro growth of Fusarium spp. In Citrus deliciosa Tenore seedlings, Fusarium spp. can be considered weak pathogens.