Abstract
Yeasts are distributed in all environments and have been reported as potential biocontrol agents against various phytopathogenic fungi. To investigate their enzymatic and biological activities, 32 yeasts were isolated from 15 date vinegar samples. Evaluation of the antagonistic activities of isolated yeasts against the plant pathogens Fusarium oxysporium, Sclerotinia sclerotiorum, and Macrophomina phaseolina indicated that there are two yeasts had the highest inhibitory effect against plant pathogens, these yeasts identified as Kluyveromyces marxianus and Torulaspora delbrueckii using traditional and molecular methods. These yeast isolates were tested for fungal cell wall degrading enzymes (in vitro), and results indicated that the yeasts had strong protease and amylase enzyme activity and moderate chitinase and cellulase enzyme activity. The antagonistic activities of each yeast were evaluated using a dual culture technique. The results showed that K. marxianus inhibited the mycelial growth of F. oxysporium, S. sclerotiorum, and M. phaseolina by 70.5, 57.5, and 75.5%, respectively, whereas T. delbrueckii inhibited mycelial growth of F. oxysporum, S. sclerotiorum, and M. phaseolina by 55.3%, 66.2%, and 31.11%, respectively. The biofilm production assay indicated that the tested yeast could form biofilms as a mechanism of antagonistic activity against phytopathogenic fungi.
Highlights
Yeasts are widespread organisms in nature and are often isolated from sugar-rich food; yeasts can be found on fruit surfaces, in plant secretions such as Aloe vera, in the soil, as many of them are associated with different insects, and are found in pickles[1,2]
These yeast isolates were tested for fungal cell wall degrading enzymes, and results indicated that the yeasts had strong protease and amylase enzyme activity and moderate chitinase and cellulase enzyme activity
The results showed that K. marxianus inhibited the mycelial growth of F. oxysporium, S. sclerotiorum, and M. phaseolina by 70.5, 57.5, and 75.5%, respectively, whereas T. delbrueckii inhibited mycelial growth of F. oxysporum, S. sclerotiorum, and M. phaseolina by 55.3%, 66.2%, and 31.11%, respectively
Summary
Yeasts are widespread organisms in nature and are often isolated from sugar-rich food; yeasts can be found on fruit surfaces (berries, grapes, apples, and peaches), in plant secretions such as Aloe vera, in the soil, as many of them are associated with different insects, and are found in pickles[1,2]. The biological control of plant fungal diseases by yeasts has been an important area of study due to the several antagonist characteristics displayed by yeasts towards fruit and beverage spoilage microorganisms, with which they compete for nutrients and space[8,9] Yeasts secrete enzymes such as β-glucosidase, cellulase, amylase, protease, and chitinase that degrade the cellular components of harmful microorganisms, a common feature in several types of host-pathogen interactions and regularly reported in antagonistic yeasts and implicated in their biocontrol activity[10,11,12]. The antagonistic activity and production of lethal toxins by T. delbrueckii isolated from spontaneously fermenting grape musts and fruits against some fungal pathogens have been reported in previous studies[20,21,22,23]. The present study aimed to evaluate the antagonistic activity of K. marxianus and T. delbrueckii isolated from Iraqi date vinegar against some fungal pathogens
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