Abstract

Thirty-one endophytic streptomycete and non-streptomycete actinobacteria were isolated from healthy date palm root tissues. In vitro screening revealed that the antifungal action of isolate #16 was associated with the production of cell-wall degrading enzymes, whereas with diffusible antifungal metabolites in isolate #28, albeit their production of volatile antifungal compounds. According to the 16S rRNA gene sequencing, isolates #16 and #28 were identified as Streptomyces polychromogenes UAE2 (Sp; GenBank Accession #: OK560620) and Streptomyces coeruleoprunus UAE1 (Sc; OK560621), respectively. The two antagonists were recovered from root tissues until 12 weeks after inoculation, efficiently colonized root cortex and xylem vessels, indicating that the date palm roots are a suitable habitat for these endophytic isolates. At the end of the greenhouse experiments, the development of sudden decline syndrome (SDS) was markedly suppressed by 53% with the application of Sp and 86% with Sc, confirming their potential in disease management. Results showed that the estimated disease severity indices in diseased seedlings were significantly (p < 0.05) reduced from 4.75 (scale of 5) to 2.25 or 0.67 by either Sp or Sc, respectively. In addition, conidial numbers of the pathogen significantly (p < 0.05) dropped by 38% and 76% with Sp and Sc, respectively, compared to infected seedlings with F. solani (control). Thus, the suppression of disease symptoms was superior in seedlings pre-inoculated with S. coeruleoprunus, indicating that the diffusible antifungal metabolites were responsible for F. solani retardation in these plants. This is the first report of actinobacteria naturally existing in date palm tissues acting as microbial antagonists against SDS on date palm.

Highlights

  • A total of 31 different endophytic actinobacteria were isolated according to their cultural characteristics on inorganic salt starch agar (ISSA) plates, of which 24 streptomycete actinobacteria (SA) (77.4%) and 7 non-streptomycete actinobacteria (NSA) (22.6%) isolates were identified (Figure S1)

  • According to [29], F. solani-inoculated plants (Fs). solani is the most abundant fungal pathogen associated with date palm root diseases in the United Arab Emirates (UAE)

  • Chemical-based means is known for their curative properties to suppress the fungal pathogen infection on host plants

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Summary

Introduction

Plant diseases caused by phytopathogens seriously result in the global crop yield reduction and severely cause billions of dollars’ worth of losses each year. Fungal diseases of plants can cause devastating damage to crops, threaten food security, and have the potential to hamper tourism [1,2,3]. Effective, and eco-friendly methods (i.e., biocontrol) may limit the presence of fungal pathogens and/or suppress their destroying activities [5,6,7]. Such methods have recently received more attention for management of fungal diseases

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