Streptomyces globosus UAE1, a Potential Effective Biocontrol Agent for Black Scorch Disease in Date Palm Plantations

Abstract

Many fungal diseases affect date palm causing considerable losses in date production worldwide. We found that the fungicide Cidely® Top inhibited the mycelial growth of the soil-borne pathogenic fungus Thielaviopsis punctulata, the causal agent of black scorch disease of date palm, both in vitro and in vivo. Because the use of biocontrol agents (BCAs) can minimize the impact of pathogen control on economic and environmental concerns related to chemical control, we aimed at testing local actinomycete strains isolated from the rhizosphere soil of healthy date palm cultivated in the United Arab Emirates (UAE) against T. punctulata. The selected isolate can thus be used as a potential agent for integrated disease management programs. In general, the BCA showed antagonism in vitro and in greenhouse experiments against this pathogen. The most promising actinomycete isolate screened showed the highest efficacy against the black scorch disease when applied before or at the same time of inoculation with T. punctulata, compared with BCA or fungicide application after inoculation. The nucleotide sequence and phylogenetic analyses using the 16S ribosomal RNA gene with other Streptomyces spp. in addition to morphological and cultural characteristics revealed that the isolated UAE strain belongs to Streptomyces globosus UAE1. The antagonistic activity of S. globosus against T. punctulata, was associated with the production by this strain of diffusible antifungal metabolites i.e., metabolites that can inhibit mycelial growth of the pathogen. This was evident in the responses of the vegetative growth of pure cultures of the pathogen when exposed to the culture filtrates of the BCA. Altogether, the pathogenicity tests, disease severity indices and mode of action tests confirmed that the BCA was not only capable of suppressing black scorch disease symptoms, but also could prevent the spread of the pathogen, as a potential practical method to improve disease management in the palm plantations. This is the first report of an actinomycete, naturally occurring in the UAE with the potential for use as a BCA in the management of the black scorch disease of date palms in the region.

Molecular Characterization and Disease Control of Stem Canker on Royal Poinciana (Delonix regia) Caused by Neoscytalidium dimidiatum in the United Arab Emirates

“…This was clear in seedlings sprayed with Cidely ® Top possessing the lowest conidial counts and the least number of defoliated leaves, indicating that this fungicide could be a potent fungicide for the management of N. dimidiatum affecting royal poinciana trees. The result of Cidely ® Top is in agreement with previous studies indicating high effectiveness of this fungicide against a number of fungal pathogens attacking trees such as T. punctulata, L. theobromae and F. solani that were almost completely inhibited [19,22,42]. To a lesser extent, Amistar Top ® was not as effective as Protifert ® or Cidely ® Top in reducing the pathogenic activities of N. dimidiatum in greenhouse trials.…”

“…Eventhough Amistar Top ® and Cidely ® Top were difenoconazole-based fungicides sharing the same concentration of the active ingredient; the superior efficiency of Cidely ® Top over Amistar Top ® could be attributed to the presence of cyflufenamid as an additional active ingredient leading to increased inhibition levels of N. dimidiatum. Difenoconazole was ineffective against Fusarium magniferae [44], but it was significantly capable for managing other diseases [17,18,42,45,46], including stem canker on royal poinciana in the current study ( Figure 7). This can be disputed to the fungicide application methods, active ingredient concentrations, plant growth conditions or pathogen responses.…”

“…Recent reports have shown that in vitro tests along with greenhouse experiments are essential to determine the sensitivity of plant pathogens to chemical and/or biological treatments [17][18][19]22,42]. According to our greenhouse experiments, Cidely ® Top, followed by Protifert ® and then Airone Liquido ® were effective on diseased seedlings of royal poinciana.…”

“…This was evidenced by the abnormalities seen in hyphal morphology, septal formation, cytoplasmic contents and the deformation of conidia following fungicide treatments ( Figure 5). Previously, Cidely ® Top exhibited the strongest inhibition of mycelial growth of T. punctulata and L. theobromae in petri dish experiments [17,42]. The same fungicides were further evaluated in vivo using apple fruit bioassay ( Figure 6).…”

“…So far, there are no reports to evaluate Cidely ® Top or any systemic fungicide on royal poinciana trees infected with N. dimidiatum under field conditions. Thus, the same fungicide was found to be highly effective against plant pathogenic fungi on date palm and mango [18,19,42]. Accordingly, a field experiment was carried out to assess the efficacy of Cidely ® Top on naturally infested royal poinciana plants.…”