Sporulation succession

Heterokaryotic hybrids also can be produced by fusing protoplasts to overcome genetic barriers to anastomosis (33. 34. Plasmid-mediated transformants have been successfully produced (TeBeest D.O., unpublished data) in this fungus and with several other Colletotrichum species (35-37). To date, genetic exchange appears limited in Colletotrichum and hybrid isolates often exhibit reduced fitness characterized by reduced growth and sporulation and decreased virulence. 

If sporulation is insufficient, the same procedure may be repeated with commeal agar or potato agar, which is sometimes successful. If this fails too, a number of additional tests exist for the identification of dermatophytes, including urea hydrolysis, in vitro hair perforation test, growth on polished rice grains, temperature enhancement or tolerance tests as well as numerous tests for the detection of special nutritional requirements, e.g. thiamine, niacin. 

This study also confirms an inferior competitive ability of the resistant strains compared with the wild-type strains [30]. On agar medium, however, the resistant and sensitive isolates did not differ in mycelium growth and sporulation [31]. Because of the lower fitness of resistant strains compared with sensitive strains, the resistant strains disappeared under field conditions in the absence of selection pressure by the antibiotic. Kasugamydn has again been successfully used to control rice blast, either in combination or by alternating application of fungicides displaying different modes of action [13, 19]. 

The successful maintenance of a pure culture system requires that isolated cultures are given the minimum exposure to conditions which either induce mutation, propagate mutant cells, or encourage sporulation. Furthermore the method chosen should maintain the cells in a state of high viability. 

Possibly, plants react with declining photosynthesis to withdraw the necessary substrates from the fungus. In this moderately resistant way, the plant looses some leaves or leaf areas, but prevents a more successful sporulation and consequently a further propagation of the parasite. 

Probably the most significant stumbling block in successful routine laboratory identification of Brettanomyces and Dekkera lies in the fundamental requirements of taxonomic guides to demonstrate the presence (or absence) of a sexual phase in the life cycle of the yeast. Dekkera requires a sporulation medium that includes augmentation with several vitamins (see Procedure 3.5.2). Required in microgram and milligram amounts, these nutrients are not easily and routinely supplied in most production-oriented laboratories. Hagan (1979) notes that even under ideal conditions, relatively poor sporulation (<1%) is observed. As a result, suspect isolates are often reported as Brett-like or Brettanomyces/Dekkera. ... 

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