Witches' broom disease (WBD) is caused by the hemibiotrophic basidiomycete fungus Crinipellis perniciosa, which is one of the most important diseases of cocoa in the western hemisphere. In this study, the contents of soluble sugars, amino acids, alkaloids, ethylene, phenolics, tannins, flavonoids, pigments, malondialdehyde (MDA), glycerol, and fatty acids were analysed in cocoa (Theobroma cacao) shoots during the infection and development of WBD. Alterations were observed in the content of soluble sugars (sucrose, glucose, and fructose), asparagine and alkaloids (caffeine and theobromine), ethylene, and tannins. Ethylene and tannins increased prior to symptom development and declined with the death of the infected tissues. Furthermore, MDA and glycerol concentrations were higher in infected tissue than in the controls, while fatty acid composition changed in the infected tissues. Chlorophylls a and b were lower throughout the development of the disease while carotenoids and xanthophylls dropped in the infected tissue by the time of symptom development. These results show co-ordinated biochemical alterations in the infected tissues, indicating major stress responses with the production of ethylene. Ethylene levels are hypothesized to play a key role in broom development. Some of the other biochemical alterations are directly associated with ethylene synthesis and may be important for the modification of its effect on the infected tissues.

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SU MMARYDespite previous research on mycorrhizal association with plants, the data on associations with coffee (Coffea species) are very sparse despite the great economic importance of this crop for many tropical developing countries. The present paper reviews the main aspects of the association between arbuscular mycorrhizal fungi (AMF) and coffee plants. This review includes topics on mycorrhizal effects on coffee nutritional status, pathogen-AMF interactions and responses to several environmental stresses. It also summarizes findings about the natural occurrence of AMF in different soils in which coffee is cultivated, some ecological aspects of this specific association and outlines trends for future investigations, which must elucidate the real benefits of mycorrhizae to coffee plants.

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