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Witches’ broom disease (WBD) of cacao, caused by the hemibiotrophic fungus, Crinipellis perniciosa, exhibits a succession of symptoms that are caused by the biotrophic phase of the fungus. However, the study of this biotrophic phase is limited by its exclusive growth inside the plant or in the presence of callus. Here we report for the first time a method for the growth and maintenance of the biotrophic-like phase of C. perniciosa on a defined medium with metabolites found in the diseased tissues. Our results suggest that glycerol is a key carbon source for this interaction. This is a crucial achievement toward understanding the biology of this fungus during the infectious phase of WBD. [ABSTRACT FROM AUTHOR]

Facultatively sexual entomopathogenic nematodes are a promising model for the experimental study of the adaptive values of sex. Our experiments in the laboratory showed that entomopathogenic nematodes display at least two different strategies in regulating the degree of amphimix as a response to nutritional stress. One strategy promotes the production of males, amphimix and the genetic variability of the offspring, improving the chances for a successful new adaptation. Another strategy increases the production of hermaphrodites at the expense of males, increasing the total number of reproductive individuals and thus the total number of offspring produced. Surprisingly, the strategy used depends upon the strain of symbiotic bacteria the nematodes are growing. The relevance of the results, in helping to discriminate between rival theories for the evolutionary maintenance of sex, is discussed. [ABSTRACT FROM AUTHOR]