Abstract
Date palm (Phoenix dactylifera L.) is the most important edible fruit crop in Saudi Arabia. Date palm cultivation and productivity are severely affected by various fungal diseases in date palm-producing countries. In recent years, black scorch disease has emerged as a devastating disease affecting date palm cultivation in the Arabian Peninsula. In the current survey, leaves and root samples were collected from deteriorated date palm trees showing variable symptoms of neck bending, leaf drying, tissue necrosis, wilting, and mortality of the entire tree in the Al-Ahsa region of Saudi Arabia. During microscopic examination, the fungus isolates growing on potato dextrose agar (PDA) media produced thick-walled chlamydospores and endoconidia. The morphological characterization confirmed the presence of Thielaviopsis punctulata in the date palm plant samples as the potential agent of black scorch disease. The results were further confirmed by polymerase chain reaction (PCR), sequencing, and phylogenetic dendrograms of partial regions of the ITS, TEF1-α, and β-tubulin genes. The nucleotide sequence comparison showed that the T. punctulata isolates were 99.9–100% identical to each other and to the T. punctulata isolate identified from Iraq-infecting date palm trees. The pathogenicity of the three selected T. punctulata isolates was also confirmed on date palm plants of Khalas cultivar. The morphological, molecular, and pathogenicity results confirmed that T. punctulata causes black scorch disease in symptomatic date palm plants in Saudi Arabia. Furthermore, seven commercially available fungicides were also tested for their potential efficacy to control black scorch disease. The in vitro application of the three fungicides Aliette, Score, and Tachigazole reduced the fungal growth zone by 86–100%, respectively, whereas the in vivo studies determined that the fungicides Aliette and Score significantly impeded the mycelial progression of T. punctulata with 40% and 73% efficiency, respectively. These fungicides can be used in integrated disease management (IDM) strategies to curb black scorch disease.
Highlights
Date palm (Phoenix dactylifera L.) is the most extensively cultivated fruit tree plant in extreme arid and semi-arid regions due to its socio-economic and significant nutritional value [1]
Date palm trees with progressed fungal infection and that were showing typical black scorch disease symptoms were found in the eastern region of Saudi Arabia
Other symptoms associated with the black scorch disease that were observed in the date palms were the drying of all of the leaves and, absolute destruction of plants during the later stage of disease development (Figure 1)
Summary
Date palm (Phoenix dactylifera L.) is the most extensively cultivated fruit tree plant in extreme arid and semi-arid regions due to its socio-economic and significant nutritional value [1]. T. paradoxa (anamorph of C. paradoxa) and T. punctulata (anamorph of C. radicicola) have been reported to be the causal agents of neck bending, wilting, black scorch, rhizosis, and chlorosis in young leaves in the Arabian Peninsula and in other major date palm-producing countries [8,9] These fungi infect a wide range of host plants, including coconut, palms, pineapple, and sugarcane [10,11]. Black scorch disease can cause economic losses to the date palm industry and may result in losses of newly planted off-shoots of ~50% [4] This disease has a wide ecological distribution, with T. paradoxa being the major disease-causing agent on date palm plantations in Iran [12], Iraq [13], Italy [14], Kuwait [15], Oman [8], Qatar [16], Saudi Arabia [17,18], and the United States [19]. T. punctulata has been found to cause black scorch infestation on date palm trees in Oman [20], Qatar [16], and more recently, in the United Arab Emirates [5]
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