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Sustainable Biocontrol of Cacao Diseases with Endophytic Bacillus spp.

Investigating the impact of applying endophytic Bacillus spp. for biocontrol of cacao diseases on native microbial communities. Focus on Bacillus pumilis ET for reducing cherelle wilt and witches' broom. Potential niche displacement effect and future research directions.

michaeljjohnson
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Sustainable Biocontrol of Cacao Diseases with Endophytic Bacillus spp.

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  1. Department of Plant Pathology Impact of application of endophytic Bacillus spp. for biocontrol of cacao diseases on native microbial communities Rachel L. Melnick Ph.D. Candidate Department of Plant Pathology The Pennsylvania State University

  2. Theobroma cacao L. • Tropical understory perennial • Seeds processed into chocolate • Home to wide range of fungal endophytes

  3. Diseases of cacao • Main limiting factor

  4. Biological Control: Pod Diseases • Cherelle wilt • Thought to be physiological thinning mechanism • Likely has biological component • Frosty Pod • Black Pod • Witches’ broom • Focus on biocontrol for disease management

  5. Hypothesis • Endophytic Bacillus spp. may provide sustainable control of cacao diseases, through activation of plant defense mechanisms and alteration of the microbial ecology of tree

  6. Bacterial endophytes • Bacillus spp. isolated from pods, leaves, branches, floral cushions at the INIAP station in Pichilingue, Ecuador • Screened for elite qualities for biocontrol agent • Identified 4 potential biological control agents

  7. Biological Control: Witches’ Broom • Bacillus pumilis ET reduced overall disease severity through dry and rainy seasons

  8. Biological Control: Pod Diseases • B. pumilis ET reduced cherelle wilt in genotype CCN-51, but not diseases • See poster P-714 for more information…

  9. What is known to date… • Bacillus pumilis ET works as a biological control agent, but how? • Antibiosis – Reduced growth of M. roreri, M. perniciosa, and P. capsici & chitinase producer • Induced resistance – Activates expression of cacao defense genes • Niche displacement?

  10. Niche displacement • Thought that most endophytes are neutral in terms of plant health • Introducing beneficial endophytes likely displaces neutral microbes to increase benefits • How to test?

  11. The trees… • Sprayed branches of cacao trees in cardinal directions with 1x108 CFU/ml at beginning of rainy season (Jan) & again in end of March • Three replicate trees per treatment • Collected leaves from branches in March and May • Preserved and shipped in RNALater

  12. ARISA • Automated Ribosomal Intergenic Spacer Analysis • Extracted genomic DNA • Nested PCR with bacillispecific primers following Garbeva et al. 2003 tRNA 16S 23S Microb Ecol. 2003. 45: 302-316

  13. Abundance & Diversity in March Applied species

  14. Abundance in May

  15. Witches’ Broom May Sampling Reapplication

  16. Conclusions • B. pumilis ET appears to decrease diversity of native microbes • Indications that application of B. pumilis ET may displace neutral endophytes

  17. Future work… • Statistical analysis of the data presented today to get more exact measures of diversity & abundance • ARISA with universal bacterial primers • As soon as I get home! • ARISA with universal fungal primers • ARISA of pods

  18. Acknowledgements • Travel Support: • APS Potomac Division Travel Award • The Eddie Echandi & H. David Thurston Award APS Foundation Award • Penn State College of Ag. Sci. Student Travel Award • Research Support: • USAID IPM-CRSP • USDA-ARS SPCL • Penn State College of Ag. Sci. Graduate Student Competitive Grant • Penn State • Paul Backman • Scott Geib • USDA-ARS SPCL • Bryan Bailey • INIAP-EET • Carmen Suárez • Karina Solis • Danilo Vera

  19. Questions????

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