Citrus greening disease (aka Huanglongbing, or HLB) is a bacterial disease affecting citrus trees across the United States. HLB is caused by Candidatus Liberibacter asiaticus (CLas), which resides in the phloem of citrus trees, causing discolored and bitter fruit, and ultimately killing the tree. Despite citrus trees being clonally propagated (and therefore genetically identical), HLB-infected trees are often found growing in close proximity to asymptomatic citrus trees. This suggests a non-genetic factor is providing protection against CLas. We hypothesized that natural products produced by endophytic microorganisms might be responsible for this apparent resistance. Endophytic bacteria and fungi were isolated from symptomatic and asymptomatic trees in HLB-infected orchards in Florida. The isolated endophytes were cross-streaked against Liberibacter crescens, a culturable surrogate for CLas, to determine which endophytes could be providing protection to asymptomatic trees. Using bioassay-guided isolation, we have begun to isolate the natural products produced by Cladosporium sp. and Epicoccum nigrum.

Bioassay-guided isolation of fungal natural products for fighting citrus greening disease

2019 Spring National Meeting

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