Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2011
Publication Date: 4/3/2011
Citation: Melnick, R.L., Bailey, B.A., Backman, P.A. 2011. Isolation of endophytic endospore-forming bacteria from Theobroma cacao as potential biological control agents of cacao dieseases. Biological Control. 57:236-245. Interpretive Summary: Theobroma cacao (cacao), the source of cocoa, suffers from several major diseases resulting in severe reductions in yield in many production areas. Cocoa is combined with United States agricultural commodities providing a benefit to the American farmer. Chemical and cultural control measures for controlling cacao diseases are expensive to employ and are often ineffective. Beneficial fungi (endophytes, microbes that live inside plants) that reduce cacao diseases have been identified in cacao, but the presence of beneficial bacteria in cacao has not been studied. We isolated and characterized a diverse set of beneficial bacteria from cacao. We identified beneficial bacterial that reduced disease when applied to cacao in growth chambers and in the field. This data suggest beneficial bacteria can be used to control cacao diseases as a part of a sustainable integrated pest management system. By providing cacao farmers with sustainable, inexpensive strategies for control of cacao diseases, cocoa supplies may be stabilized resulting in increased benefits to the cacao farmer, the cocoa industry, and the American farmer.
Technical Abstract: Endospore-forming bacterial endophytes were isolated from Theobroma cacao to access the present and diversity of endospore-forming bacteria in cacao. Cacao leaves, pods, branches, and flower cushions were removed from cacao trees escaping disease on INIAP’s Tropical Research Station in Pichilingue, Ecuador. Tissue was surface sterilized, heat treated (75°C for 15 min) and plated onto tryptic soy agar. Sixty nine distinct endophytic endospore-forming bacteria were isolated. The 16S rRNA gene was sequenced to determine species identity, then the isolates wee further classified for characteristics of biological control activity of chitinase production and antagonism. Sixteen isolates were chitinolytic. In antagonism studies against cacao pathogens, 42% were antagonistic to Moniliophthora roreri, 33% to M. perniciosa, and 49% to Phytophthora capsici. Twenty-five percent of isolates inhibited the growth of both Moniliophthora spp., while 22% of isolates inhibited the growth of all three pathogens. Isolates that were chitinolytic and tested negative on Bacillus cereus agar were tested in planta studies. All (14)isolates were capable of endophytic colonization, while 8 isolates inhibited lesion formation in response to P. capsici inoculation in detached leaf assays. This research illustrates both the presence of endophytic bacteria in cacao trees and their potential as biological control agents of cacao pathogens.