Abstract:
The biocontrol potential of Trichoderma harzianum Rifai,
Trichoderma polysporum (Link.:Pers.) Rifai, Scytalidium aurantiacum
Klingstr. et Beyer or a Penicillium sp. against Trametes versicolor
(L. :Fr.) Pilat, Neolentinus lepideus (Fr.) Redh. et Ginns, Postia
placenta (Fr.) M.Lars. et Lomb. and Irpex lacteus Fr. was evaluated
using agar plate, soil bottle and small size wood wafer tests. Although
T. harzianum arrested growth of several wood decay fungi, it never
killed them on wood samples. Of the tested microfungi, S. aurantiacum
performed best in the wood-based assays.
At the same time, the utility of small size wood assays for
evaluation of biocontrol potential was demonstrated. Such assays are
more rapid and versatile than full-scale soil bottle or sawdust tube
tests, and provide more information than agar plate screenings.
Microscopic examination of hyphal interactions between T.
versicolor and T. harzianum on microscope slide cultures yielded little
additional information, partly due to the experimental system chosen.
No hyphal interference or lysis of cell walls was observed, possibly due
to the high nutrient levels in the slide cultures.
The activities of enzymes related to wood decay were studied in
pure and mixed liquid cultures of T. versicolor and T. harzianum at low
(0.4 mM) and high (4 mM) nitrogen concentrations. In high nitrogen
medium, total filter paper cellulase, specific and total cellobiase, and
specific and total laccase increased when compared to activities
obtained in low nitrogen concentrations. Conversely, specific filter paper cellulase and peroxidase activities were enhanced under nitrogen
limiting conditions.
Influences of T. harzianum on extracellular enzyme production of
T. versicolor were observed. Total and specific laccase activities were
induced in media containing both low and high nitrogen levels, whilst
filter paper cellulase activities decreased. Peroxidase and cellobiase
activities remained at approximately the same level or were decreased in
mixed cultures.
The experimental system chosen allowed no separation of mycelia or
culture liquids of the two fungi incubated in mixed culture. Therefore,
few conclusions with respect to induction, inhibition or regulation of
the monitored enzymes could be reached. None of the enzyme activities
was correlated with biomass production. Laccases and Poly R-478
peroxidase activity indicated survival of the T. versicolor, since T.
harzianum did not produce these two enzymes.
