رسائل دكتوراة
English
2021
Chemical And Biological Control Of Canker Disease Of Delonix Regia Caused By The Fungus Neoscytalidium Dimidiatum
Khaled El-Tarabily, Seham Mohammed Suliman Mohammed Al-Raish
كلية العلوم-جامعة الإمارات العربية المتحدة · الامارات
In the United Arab Emirates (UAE), royal poinciana ( Delonix regia ) trees suffer from stem canker disease. Symptoms of stem canker can be characterized by branch and leaf dryness, bark lesions, discoloration of xylem tissues, longitudinal wood necrosis and extensive gumming. General dieback signs were also observed leading to complete defoliation of leaves and ultimately death of trees in advanced stages. The fungus, Neoscytalidium dimidiatum DSM 109897, was consistently recovered from diseased royal poinciana tissues; this was confirmed by the molecular, structural and morphological studies. Phylogenetic analyses of the translation elongation factor 1-a (TEF1-α) of N. dimidiatum from the UAE with reference specimens of Botryosphaeriaceae family validated the identity of the pathogen. To manage the disease, the chemical fungicides, Protifert ® , Cidely ® Top and Amistrar ® Top, significantly inhibited mycelial growth and reduced conidial numbers of N. dimidiatum in laboratory and greenhouse experiments. The described “apple bioassay”is an innovative approach that can be useful when performing fungicide treatment studies. Under field conditions, Cidely ® Top proved to be the most effective fungicide against N. dimidiatum among all tested treatments. The data suggest that the causal agent of stem canker disease on royal poinciana in the UAE is N. dimidiatum . In addition to the fungicides application, the current theory also studied the effect of biological control agents to control this disease. The current study also revealed that 47 actinobacterial isolates were obtained from rhizosphere soils of royal poinciana in the UAE, among which streptomycete actinobacteria were the predominant isolates. Three isolates, Streptomyces rochei UAE2, S. coelicoflavus UAE1 and S. antibioticus UAE1, exhibited powerful in vitro antifungal activity against N. dimidiatum . The antifungal action of S. rochei and S. coelicoflavus was mainly correlated with antibiosis and cell-wall-degrading enzymes production, respectively. S. antibioticus was, however, associated with both mode of actions . Using the novel apple fruit bioassay, these isolates suppressed lesion development on fruits inoculated with N. dimidiatum . Under greenhouse conditions, each of the potential Biological Control Agents (BCAs) showed greater efficacies against stem canker when applied before N. dimidiatum inoculation (preventive) than those when the same BCAs were applied after the pathogen (curative) or the pathogen alone (control). The curative effects of Cidely ® Top (a chemical fungicide) and S. antibioticus on disease symptoms were comparable on royal poinciana. Prior to pathogen inoculation, S. antibioticus was capable to suppress disease symptoms and prevent the pathogen spread, suggesting a relative superiority of S. antibioticus over all other chemical and biological treatments tested. In conclusion, the multiple mode of actions in S. antibioticus can be particularly effective to produce synergistic actions against the fungus. This study is the first to explore the potential to use both biocontrol and fungicides to further develop an integrated disease management strategy against stem canker disease in royal poinciana.