Filogenia e patogenicidade de fungos endofíticos associados à raízes de mandioca em Pernambuco

Abstract

Manihot esculenta Crantz is a species of the Euphorbiaceae family, has characteristics of a bushy plant, which exhibits a root system rich in starch and represents a source of essential carbohydrates for human and animal food. Root diseases can be caused by several etiological agents, among which fungi have a greater prominence, due to their high incidence and difficulty of control. Among the pathogens already reported as causing root rot in cassava, we can highlight: Phytophthora spp., Fusarium spp., Lasiodiplodia spp., Neocytalidium dimidiatum and Macrophomina pseudophaseolina. Studies have shown that several species known as plant pathogens can also survive as endophytes, being present inside plants without causing harm or apparent damage. However, under conditions of host stress, such as biological pressure from pests, pathogens and abiotic stresses, some endophytic fungi may act as opportunistic pathogens. Thus, several crops of agricultural importance may be colonized by these opportunistic pathogens. Therefore, the objective of the present study was to investigate the diversity and evaluate the pathogenicity of endophytic fungal species associated with healthy cassava roots cultivated in areas in the state of Pernambuco. The collections were carried out in 12 cultivated areas, in the regions of Zona da Mata (Chã Grande, Primavera and Condado), in the Agreste (São João and Garanhuns) and in the Sertão (Araripina) in the state of Pernambuco and were sent to the Laboratório of Micologia Ambiental from the Departamento of Micologia at the Universidade Federal of Pernambuco, where the endophytic fungi were isolated. Fungal identifications were based on studies of the morphology of vegetative structures, as well as molecular analyses. According to data found in the Fungal Database (https://nt.arsgrin. gov/fungaldatabases/), the selection of isolates for phylogenetic analyzes and pathogenicity testing used the criterion that the selected genera had already been reported associated with cassava roots and often known to cause postharvest rot. In the pathogenicity test, the treatments were represented by 12 species contained in the genera of Neocosmospora, Acremonium, Penicillium, Aspergillus and Talaromyces. Differences between treatments were assessed based on lesion size. Data were subjected to analysis of variance (ANOVA) and means were compared by Tukey's test at 5% probability using the SISVAR program. A total of 78 endophytic fungal isolates belonging to 21 genera were identified. Among them is the genus Neocosmospora of agronomic importance, known to cause rot in cassava roots. Genera associated with postharvest rot such as Penicillium, Aspergillus and Talaromyces were also obtained. Two isolates of a possible new species of Aspergillus were found (Aspergillus sp. 1 ARM 1078 and Aspergillus sp. 2 ARM 1082) forming a clade close to Aspergillus iranicus. In the pathogenicity test, although all isolates evaluated formed lesions, the isolates Neocosmospora falciforme ARM 1104, Talaromyces lentulus ARM 1083 and Aspergillus tabacinus ARM 1094 differed from the control in terms of the size of the lesion caused, thus they were the most aggressive isolates. Finally, according to the results obtained in this study, it was possible to verify the relationship between endophytic and pathogenic isolates in cassava roots in areas in the state of Pernambuco, and it can be concluded that species already reported as phytopathogenic can be found in asymptomatic roots.