Screening of bacteria for antagonistic activity against phytopathogens of avocados

Avocado trees in Florida and California are under attack, respectively, from laurel wilt and Fusarium dieback, two diseases caused by fungi that live in symbiosis with ambrosia beetle species. As a first step to identify possible bacteria that can be utilized as biocontrol agents against these important diseases of avocados, we isolated microorganisms from avocado trees in Florida to determine their potential for use as biocontrol antagonists against the pathogens responsible for laurel wilt and Fusarium dieback. In addition, we assessed the potential of other strains not isolated from avocado to determine their effectiveness as biocontrol antagonists. A total of 50 strains were identified as strong antagonists against the laurel wilt pathogen, Raffaelea lauricola. Fifteen of the most active strains were, in turn, evaluated for antagonism against Fusarium euwallaceae, the causal agent of Fusarium dieback on avocados. Four strains representing three Paenibacillus species and one Bacillus species were found to be active against both R. lauricola and F. euwallaceae. This study is the first to report antifungal or antagonist activity of bacterial strains effective against avocado pathogens vectored by ambrosia beetles, and it is also the first to report the effectiveness of Paenibacillus thiaminolyticus or Paenibacillus apiarius against a phytopathogen.

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