Biocontrol Potential of Endophytic Actinobacteria against Fusarium solani, the Causal Agent of Sudden Decline Syndrome on Date Palm in the UAE

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.

The Multifarious Endophytic Actinobacterial Isolate, Streptomyces tubercidicus UAE1, Combined With the Seaweed Biostimulant Further Promotes Growth of Avicennia marina

“…Previously, in vitro investigations followed by preliminary in vivo studies have successfully identified rhizosphere-competent and endophytic PGPA of various mechanisms in Salicornia (El-Tarabily et al, 2019;Mathew et al, 2020), mangroves (El-Tarabily et al, 2021a;El-Tarabily et al, 2021b), and other plant species (Al Hamad et al, 2021;Alblooshi et al, 2022). An extensive in vitro screening was carried out in the current study to find the suitable salt-tolerant endophytic PGPA strains producing high levels of PGRs (auxins, CKs, GA 3 , and PAs) and possessing ACCD activity.…”

The 1-aminocyclopropane-1-carboxylic acid deaminase-producing Streptomyces violaceoruber UAE1 can provide protection from sudden decline syndrome on date palm

“…Plants were kept in the greenhouse for 35 days post-treatment (dpt) for Experiments 1 and 2. Disease severity index was recorded for SDS symptoms at 35 dpt (Experiment 1) and at 15 and 35 dpt (Experiment 2) using a scale of 0-5: 0 = no apparent symptoms, 1 = 1-10% necrotic or white area in leaves or rotting in roots, 2 = 11-25%, 3 = 26-50%, 4 = 51-75%, and 5 = 76-100% (Alblooshi et al, 2022). For disease symptoms/recovery of diseased plants, conidial counts of F. solani were recorded at 35 dpt (Experiment 2).…”

“…Integrated disease management (IDM) combining BCAs with fungicides can be another option to reduce the impact of fungicides as well as to effectively manage plant diseases (Saeed et al, 2017b;Kamil et al, 2018;Zapata-Sarmiento et al, 2020). In that sense, actinobacteria have been constantly proposed as possible candidates to replace chemical fungicides (Saeed et al, 2017b;Kamil et al, 2018;Alblooshi et al, 2022); thus the disease management capacity of BCAs heavily relies on uncontrollable environmental conditions (Ons et al, 2020).…”

“…The genus Streptomyces is a unique subgroup of actinobacteria that are known as prolific producers of antibiotics and bioactive secondary metabolites (Goodfellow and Williams, 1983;Barka et al, 2016;Lewin et al, 2016). Many species of Streptomyces exhibit biological control potential against phytopathogenic fungi through multiple mechanisms, including the production of antibiotics, hyperparasitism, and induction of plant resistance response (Tamreihao et al, 2016;Saeed et al, 2017a;Al Hamad et al, 2021;Alblooshi et al, 2022). Such an environmentally-friendly strategy has recently received renewed attention to control plant diseases and increase crop production.…”

“…Although several reports have used beneficial fungi (e.g., Trichoderma and Chaetomium species) as BCAs to control date palm pathogens (Soytong et al, 2005;Sánchez et al, 2007;Ammar, 2011;Nishad and Ahmed, 2020), no rhizosphere actinobacterial isolates have been identified against SDS. The endophytic Streptomyces coeruleoprunus, on the other hand, has been considered a biocontrol potential against F. solani on date palm trees in the UAE (Alblooshi et al, 2022). To avoid the worst impacts of black scorch disease, the rhizosphere isolate, Streptomyces globosus UAE1 has been successfully tested to control T. punctulata on date palm (Saeed et al, 2017a).…”