Antimicrobial and plant growth-promoting properties of the cacao endophyte Bacillus subtilis ALB629.

AIMS: To investigate the effects of the endophyte Bacillus subtilisALB629 on the growth of cacao seedlings at early developmental stage and to evaluate its antimicrobial properties. METHODS AND RESULTS: Germinating cacao seeds were inoculated with ALB629, and seedlings growth was evaluated 30 days later. Significant increase (P < 0·05) was observed in the root system (up to 30%), leaf area (14%) and stem height (7·6%). ALB629 colonized the entire plant, prevailing over indigenous micro-organisms. In addition, it was tested in vitro, by pairing assays, and showed antagonistic effect against the phytopathogenic fungi Moniliophthora perniciosa, Colletotrichum sp. and C. gossypii. When tested in cacao-grafting procedure in the field, ALB629 increased the grafting success rate (24%), indicating its protective effect. In addition, this Bacillus secretes an antagonist compound, as shown by the antifungal activity of the cell-free culture. CONCLUSIONS: Bacillus subtilisALB629 promotes cacao root growth, besides promoting growth of the aerial part of cacao seedlings. It has antimicrobial properties and produces an antifungal compound. SIGNIFICANCE AND IMPACT OF THE STUDY: ALB629 presented beneficial characteristics for cacao cultivation, being a good biological control agent candidate. Furthermore, it is a potential source of antifungal compound with potential for commercial exploitation.

Endophytic and pathogenic isolates of the cacao fungal pathogen Moniliophthora perniciosa (Tricholomataceae) are indistinguishable based on genetic and physiological analysis.

We evaluated the genetic and physiological variability of Moniliophthora perniciosa obtained from healthy and diseased branches of cacao (Theobroma cacao) plants. The diversity of the isolates was evaluated by RAPD technique and by studies of virulence and exoenzyme production. The genetic variability of endophytic and pathogenic M. perniciosa was evaluated in association with pathogenicity assays. RAPD analysis showed eight genetic groups, which were not related to plant disease status (healthy versus diseased branches). Isolates from cacao were included in three groups, excluding isolates from other host plants. Pathogenicity and enzyme analysis showed that the virulence of the isolates is not related to exoenzyme production. This is the first evidence that M. perniciosa colonizes healthy parenchymatic tissues, showing that endophytic behavior may occur in this species.

Biochemical changes during the development of witches' broom: the most important disease of cocoa in Brazil caused by Crinipellis perniciosa.

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.