Characterization of date fruit microbiome (cv. Medjool) and development of biological control agents against fungal contamination and decay

The purpose of this study was to study and characterize microorganisms, including bacteria, fungi and yeast, inhabiting the fruit of the Madjool date.

Another purpose of the study was to evaluate biological control activity of the isolated bacteria and yeasts from date fruit to reduce the infection of the fruit by pathogenic fungi. The fruit of the Madjool species is attacked by two main fungal pathogens, Penicillium expansum and Aspergillus niger.

The molecular characterization results, indicate that the fruit peel contains a wide variety of microorganisms, of both bacteria and of fungi than in the fruit pulp, and communities vary in genera and species richness and abundance through out different stages of fruit development and ripening. The most common bacterial genus was Lactococcus, and the most common fungal genus is Penicillium. Aspergillus found to be common mainly in the ripe fruit.

About 300 isolates of bacteria and yeasts were obtained from date fruit. Their ability to inhibit the growth, of the two pathogenic fungi: P. expansum and A. niger in vitro (in agar plates) was examined. Twelve species, were able to inhibit the pathogenic fungi, four of which showed delayed growth of the two fungi: B. subtilis, B. licheniformis, B. amyloliquefacies, and B. onorensis. Low to zero effect was found, when these bacteria were tested for inhibition of these pathogenic fungi in unripe fruit.

In addition, about ten different yeast species, were isolated from the peel and the pulp of ripe fruit. Examining yeast effect on the fruit, it was found that the fruit when dipped in yeast cell suspension, resulted in a significant delay in the growth of A. niger.