The witches'-broom disease, caused by the basidiomycete Crinipellis perniciosa, is the most limiting factor for cacao cultivation in Brazil. Trichoderma stromaticum is a mycoparasite of the witches'-broom pathogen of cacao that is currently being applied in the field to manage the disease in Bahia State, Brazil. In this work, molecular and traditional
methods were used to study the genetic and biological diversity of this
mycoparasite. Ninety-one isolates, mostly collected from farms not
sprayed with the fungus, were analyzed by amplified fragment length
polymorphisms (AFLP), which showed that two genetic groups (I and II)
of T. stromaticum occur in Bahia State. This classification of T. stromaticum into two distinct AFLP groups was also in agreement with several other characteristics, including growth on agar media at different temperatures and sporulation on infected stem segments (broom pieces) and
rice grains. Group II favors higher temperatures compared with group I.
The genetic and biological differences of the isolates, however, were not
evident in field experiments, where sporulation was evaluated on the
surface of brooms under natural conditions. Our results show that there is
considerable genetic and biological diversity within T. stromaticum in Bahia and other cacao-growing regions of South America that are
affected by the witches'-broom disease. This diversity could be explored
in the development of efficient biological control agents against the
disease. Factors that may affect the application and performance of this
biocontrol agent in the field, such as sporulation on rice substrate and on
the brooms and growth at various temperatures, are discussed.
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