Peanut rust caused by Puccinia arachidis
is one of the most important peanut foliar diseases in
the world, particularly in Burkina Faso. For sustainable
peanut production, ecological disease management
strategies are needed to limit the overuse of synthetic
fungicides in the control of peanut rust. Thus,
the use of Akanthomyces lecanii, a hyperparasite of
rust fungi, may be an alternative to control peanut
rust. However, investigations of the mechanisms of
action of A. lecanii are essential before its development
as a biocontrol agent. To do so, peanut leaves
bearing rust pustules were detached, and each leaf
was sprayed with 500 μl of a suspension of A. lecanii
conidia (
106 conidia/ml) at the lower surface. Then,
each leaf was incubated in a Petri dish on moist blotting
paper, and kept in the laboratory at 20 °C, under
a 12:12 light/dark photoperiod. After 15 days incubation,
the inoculated and uninoculated rust pustules
were observed under photonic and electron microscopes
Pictures revealed that A. lecanii colonized
the urediniospores of inoculated sori. Our results
showed that the mechanisms of action of A. lecanii
on P. arachidis could involve the following events:
(i) attachment of the antagonist to urediniospores
mediated by a mucilaginous extracellular matrix; (ii)
penetration due to mechanical pressure and enzymes
action on the cell-wall; (iii) active growth of the
antagonist inside of urediniospores and digestion of
the cell content. From our study, the use of suspensions
of A. lecanii spores is a promising tool for biocontrol
of peanut rust.

Biological control, peanut, hyperpparasitism, antagonism, Rust