The fungistatic activity of a lactic acid bacterium, which had been isolated from yellow pitahaya cultures, against fungi associated with basal rot (Fusarium oxysporum and Fusarium fujikuroi) was measured in the present study.  Its activity was assessed in three fractions: fermented (S1), metabolic products (S2), and biomass (S3), using two fermentation substrates: Man Rogosa Sharpe agar (MRS) and potato dextrose agar (PDA).  The bacterium was molecularly identified as Lactobacillus plantarum.  S3 reduced F. fujikuroi growth by 100% over 48 h of fermentation, which occurred during the stationary phase of bacterial growth.  The three fractions’ fungistatic activity against F. fujikuroi depended on the substrate employed.  The fermentation kinetic parameters for L. plantarum indicated that its specific growth rate was 0.46 h^–1, with 93.63% substrate consumption, 0.045 kg kg^–1 cell yield, and 0.54 kg kg^–1 product yield.  The kinetic parameters calculated will allow for bacteria production scaling.  These in-vitro trials reveal L. plantarum’s possible application as a biocontrol agent for diseases associated with Fusarium.  However, further ex-vivo and in-vivo researches are required to demonstrate its behavior in crops. 

 

At least 20–40% of annual losses of avocado crops are caused by pathogenic fungi.  The chemical treatments of these diseases are inefficient, cause environmental pollution and are increasingly restricted by international laws.  This work aimed to assess the biocontrol capacity of a bacterial extract to protect avocado fruits and plants from pathogen infections.  Extracts from the bacterial isolate Serratia sp. ARP5.1 were obtained from liquid fermentations in a biorreactor.  A body rot postharvest infection model with Colletotrichum gloeosporioides on fruits was developed.  Moreover, packaging conditions were simulated using the bacterial extract and the commercial fungicide prochloraz as a positive control.  Additionally, seedlings infections with Phytophthora cinnamomi were performed on two types of avocado (West Indian race and cv. Hass).  The Area Under Disease Progress Curve (AUDPC) was recorded using the bacterial extract and a commercial product with fosetyl-aluminium as treatments.  The bacterial extract significantly reduced infections by C. gloeosporioides on injured avocado fruits at 31.1 µg mL^–1.  Intact fruits were also protected against body rot infections at the same concentration and showed no significant differences with the commercial fungicide.  On the other hand, AUDPC in the seedlings was significantly reduced with the extract treatment at 3 µg mL^–1 compared to the control.  However, a possible phytotoxicity effect of the extract was evidenced in the seedlings and confirmed by pathogen recovery and tests on Raphanus sativus seedlings.  Finally, formulations of the extracts (emulsion and emulsifiable concentrate) were prepared, and bioactive stability was assessed for 8 wk.  The emulsion formulates demonstrated very stable bioactivity against P. cinnamomi.  The extract and the emulsion formulate showed promising results for the control of avocado pathogens.  New bioproducts based on this type of active principles could be developed for the benefit of avocado industry.