Original article

Studies on the interaction between tropical nematophagous fungi and entomopathogenic nematodes (Rhabditida) under laboratory conditions

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Abstract:

This study settles a step toward to understanding the interaction between nematophagous fungi (NFs) generally found in the soil and entomopathogenic nematodes (EPNs) used in the control of agricultural pests. There are very few studies linking EPNs and their natural enemies around the world and none in Brazil. Therefore, we decided to test differences regarding aggressiveness and susceptibility among the fungi and EPNs found and used in this country. The aim of this work was to study the interactions between the tropical native NFs, Arthrobotrys oligospora AM2, Arthrobotrys musiformis AM4, Arthrobotrys sp. CO7, Arthrobotrys sp. CC7 and the EPNs, Heterorhabditis indica LPP30 (Heterorhabditidae), a native nematode, and Steinernema carpocapsae All (Steinernematidae), a exotic nematode, under laboratory conditions. The interaction was studied in four aspects: 1) NF aggressiveness against EPNs; 2) effect of culture medium on NF aggressiveness to infective juveniles (IJs); 3) EPN susceptibility to NFs; and 4) dispersion of IJs in two types of soil in the presence of NFs. The fungi A. musiformis AM4 and Arthrobotrys sp. CO7 were considered the most aggressive among the tested strains, since they trapped more IJs. Water agar medium provided the best conditions to test nematode-fungus interaction among the six media tested, since the fungi tested produced more trapping structures to apprehend IJs on it. Both fungi were considered very aggressive to EPNs due to their apprehension capacity. Regarding susceptibility, H. indica LPP30 IJs were more susceptible than IJs of S. carpocapsae ALL to both A. musiformis AM4 and Arthrobotrys sp. CO7 in the first 24 h of contact. However, after 48 h, the means of IJs captured by the fungi became statistically equal, except for S. carpocapsae All in Assay 2, which presented the highest mean capture rate. The fungus Arthrobotrys sp. CO7 repelled S. carpocapsae All IJs in sand at 15 cm. The more we learn about biotic factors that interfere in biocontrol, the more effective we can make it. Future studies will focus on the characterization of these interactions in the field under tropical conditions.

HIGHLIGHTS

  • Arthrobotrys musiformis AM4 and Arthrobotrys sp. CO7 were the most aggressive tropical fungi tested against Heterorhabditis indica LPP30.
  • Water agar medium provided the best conditions to test nematode-fungus interaction with lowest environmental impact among the six media tested.
  • H. indica LPP30 was more apprehended than S. carpocapsae All by both tropical fungi tested.
  • In a soil environment, there was a repellent action from Arthrobotrys sp. CO7 against S. carpocapsae All.

Keywords:

Arthrobotrys musiformis, Arthrobotrys oligospora, Steinernema carpocapsae All, Heterorhabditis indica LPP30, aggressiveness, repulsion, culture media.


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