Abstract
Problem statement: Fungal endophytes are widely studied for their potential as biocontrol agents towards fungal pathogens. In vitro assessments usually reveal their antibiosis and mycoparasitism nature, but little is understood regarding their production of volatile metabolites as mechanisms of antagonism. Approach: This study explored the potential of fungal endophytes in controlling the pathogen responsible for Fusarium wilt disease. Nine fungal endophytes were tested for their ability to inhibit the growth of the pathogenic Fusarium oxysporum F. sp. cubense race 4 (FocR4) via production of volatile inhibitory metabolites. The type of volatile metabolites produced were subsequently characterized and identified using the Gas-Chromatography Mass-Spectrophotometry (GCMS). Results: Eight of the isolates (BTF05, BTF07, BTF08, BTF15, BTF21, WAA03, WAA02, MIF01) showed positive results with percentages of inhibition varying from 1.43-31.43% while one isolate (ALF01), showed negative result (0% inhibition). Volatile profiles showed that these fungal endophytes produced between 15-47 volatile metabolites per isolate. However, the more volatile metabolites produced by a single endophyte does not indicate better biocontrol potential. Isolate BTF05 produced 47 different volatile metabolites, but has only 8.57% inhibition, compared to isolate BTF21 with 15 metabolites but a percentage of 11.43% inhibition. The potency of the volatile metabolites produced may also influenced the biocontrol potential of the fungal endophytes as some isolates such as BTF08 and MIF01 have only two to three known inhibitory metabolites but have higher PIDG values at 31.43 and 11.43%, respectively. Contrary, isolates WAA02 and WAA03 which has five to six metabolites but PIDG values of less than 3%. Conclusion: Fungal endophytes have the ability to produce several types of volatile metabolites to inhibit the growth of FocR4. These volatile inhibitory metabolites can be further extracted and the amount produced ascertained for future manipulation in biological control of FocR4.
Highlights
Endophytes are most often isolated from symptomless plants of various species (McInroy and Kloepper, 1995)
We identified the different types of volatile compounds produced by the fungal endophytes and distinguished between volatiles which may have inhibitory effect towards the fungal pathogen Fusarium oxysporum F. sp. cubense race 4 (FocR4)
Five of the eight isolates (BTF05, BTF07, BTF15, WAA02, WAA03) showed weak inhibitory effect towards FocR4 with Percentage of Inhibition of Diameter Growth (PIDG) values less than 10%, while three isolates (BTF08, BTF21 and MIF01) produced PIDG values more than 10%
Summary
Endophytes are most often isolated from symptomless plants of various species (McInroy and Kloepper, 1995). Their association with host plants are known to improve plant growth and vigour (Ting et al, 2008), enhance plant nutrient absorption (Chanway, 1996) and to potentially confer disease resistance in plants against pathogen infection (Ting et al, 2007). Of the many mechanisms of pathogen inhibition, production of antimicrobial compounds is the most detected and widely studied. The nonvolatile compounds are often detected using simple plate assay (Chaurasia et al, 2005) and the filtrates can be extracted, purified and characterized
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