Abstract
Endophytic microorganisms (EMs) have recently attracted interest for applications in plant protection, mainly due to their bioactive compound-producing capacity. Therefore, we underwent the task of isolating olive tree EMs and investigating their bioactivity against the devastating pathogen Colletotrichum acutatum. Several EMs were isolated; however, the Bacillus sp. PTA13 isolate exhibited the highest toxicity to the phytopathogen. Bacteria of the genus Bacillus exhibit superior bioactive metabolite-producing capacity, with the lipopeptides (LPs) of surfactin, iturin, and fengycin groups being the most studied. A total LP extract and several fractions were obtained, and their bioactivity was assessed against C. acutatum strains. LPs of the major surfactin, iturin, and fengycin groups and the minor gageotetrin and bacilotetrin groups were annotated. The results confirmed the bioactivity of the major LPs, with fengycins being the most fungitoxic. Interestingly, the minor LP fraction exhibited selective toxicity to the fungicide-resistant C. acutatum isolate, an observation that highlights the significance of our approach to comprehensively mine the total LP extract. This work represents a proof of concept of the exploitation of EMs in customized olive tree plant protection and aligns well with strategies that focus on the sustainability and safety of food production via the development of next-generation plant protection products.
Highlights
The quest for novel and/or alternative sources of bioactivity is necessary to address the challenges faced by the agrochemical sector in securing large quantities of high-quality food for the exponentially growing human population
The applied protocol resulted in the isolation of 53 olive tree endophytic microorganisms (EMs), out of which 29 were bacteria and 24 fungi
The grouping of the latter was based on phenotypic characteristics, the growth rate of their cultures, and microscopic observations
Summary
There is no doubt that conventional plant protection products (PPPs) represent the backbone of the agrifood sector [1,2], with more than four million tones being released annually into the agroecosystems worldwide [3]. Such dependency on conventional PPPs represents a great shortcoming for the sector, considering the inability to discover and develop bioactive molecules that exhibit new mode(s) of action (MoA) as PPPs [4,5]. The symbiotic relationship that EMs have developed through the long evolutionary process with their counterparts appears to be under the control of a complex regulatory mechanism [12]
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