Beneficial endophytic microorganisms comprise especially fungi and bacteria that colonize internal plant tissues without causing visible damage to their hosts (Petrini, 1991). They are different from phytopathogenic microorganisms because they are not detrimental, do not cause diseases to plants, and are distinct from epiphytic microorganisms which live on the surface of plant organs and tissues (Hallmann et al., 1997). Endophytic bacteria are able to penetrate and become systemically disseminated in the host plant, actively colonizing the apoplast (Quadt-Hallmann et al., 1997b), conducting vessels (Hallmann et al., 1997), and occasionally the intracellular spaces (Quadt-Hallmann et al., 1997a). This colonization presents an ecological niche, similar to that occupied by plant pathogens, and this endophytic bacteria can, therefore, act as biological control agents against pathogens (Hallmann et al., 1997).
In this sense, the suppression of plant diseases due to the action of endophytic microorganisms has been demonstrated in several pathosystems (Narisawa et al., 1998; Lima et al., 1994). Several mechanisms may control this suppression, either directly on the pathogen inside the plant by antibiosis (Sturz et al., 1998) and competition for nutrients (Mari et al., 1996), or indirectly by induction of plant resistance response (M'Piga et al., 1997).
The coffee leaf rust caused by Hemileia vastatrix is the main disease in coffee, causing yield losses of 35 to 40%, on average. Control is basically achieved by fungicides. In 2000, in Brazil, the use of fungicides in coffee stood for 3,680 t of active ingredient (Campanhola & Bettiol, 2003). Therefore, alternatives to control coffee leaf rust must be sought. The objective of this work was to select endophytic bacteria isolates from coffee leaves and branches, with biocontrol potential against coffee leaf rust, by means of inhibition assays of urediniospores germination and control of coffee leaf rust in tests with leaf discs, detached leaves, and on potted seedling of cv Mundo Novo.
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