Atividade enzimática micelial e conidial de isolados de Metarhizium anisopliae s.l. e virulência para Rhipicephalus microplus

Abstract

Metarhizium spp. is a pathogenic fungus applied to several arthropods, being globally used for control of agricultural pests and considered a promising agent to ticks such as Rhipicephalus microplus. The present study assessed the macromorphology, conidial production, rice yield, virulence for engorged R. microplus females and enzymatic activities (proteases, Pr1, Pr2, lipases and oxidative enzymes) in four Brazilian M. anisopliae sensu lato (s.l.) isolates (IBCB 116, IBCB 383, IBCB 410 and IBCB 481). Fungal growth was performed in potato-dextrose-agar media (PDA) for 15 days. Descriptions of the colony and spots from media, with consequent quantification, were performed for the analysis of morphology and conidiogenesis. The yield was determined after growth in rice and conidia mass were individually weight. Virulence was evaluated by following the biological parameters of engorged R. microplus females after immersion in aqueous suspensions (1×107 and 1×108 conidia mL-1) of each isolate.Forenzymatic activities, protein extractions were carried out in conidia (surface and intracytoplasmic fraction) and mycelia (mycelial secretion and intracytoplasmic fraction). Parametric data were analyzed by analysis of variance (ANOVA) followed by Tukey test and non-parametric by Kruskal Wallis test followed by Student-Newman-Keuls (SNK) (p<0.05). Differences number of conidia/cm² were observed among the isolates. IBCB 383 presented the highest conidial production in both BDA and rice, while the lowest number was observed in IBCB 116. When the highest concentration (1×108 conidia mL-1) was evaluated, IBCB 481 showed a higher control percentage for engorged R. microplus females (44%) and IBCB 116 again the lowest (14%). For enzymes, in general, all activities (proteases, Pr1, Pr2 and lipases) were higher in the most virulent isolates. When comparing IBCB 481 and IBCB 116, Pr1 activity was considered superior for IBCB 481 in almost 2.8 times for the conidia surface and 2.5 times for the micelial secretion, besides lipolytic activity was 5 times higher in the intracytoplasmic conidia fraction. The oxidizing activity presented variations among the isolates and in accordance with the virulence findings, formost of the analyzes, IBCB 481 exhibited the highest activities of SOD, catalase and peroxidase.Therefore, it is concluded that the association among morphological studies, virulence analysis and enzymatic characterization are important tools to be used in the selection of Metarhizium anisopliae s.l. isolates, especially for programs aiming the biocontrol of ticks such as R. microplus.