Decline and Dieback of Stone Fruit Trees in Jordan: Prevalence, Pathogenicity of Associated Fungal Species, and In Vitro Chemical Control with Selected Fungicides

Stone fruit trees are important fruit crops in Jordan and decline and dieback diseases have recently caused problems in many Jordanian orchards. This study aimed to estimate dieback and decline incidence and severity in selected orchards, to isolate and identify the causal agents associated with decline and dieback symptoms, and to test the efficacy of some fungicides against isolated pathogens. Field surveys were carried out, and representative samples of diseased trees were collected to isolate and identify the causal organisms. Molecular analyses of DNA sequences of the Internal Transcribed Spacer (ITS) regions of fungal ribosomal DNA (r-DNA) and partial sequence of the translation elongation factor (TEF1-α) gene were used to confirm the morphological identifications of the fungal isolates. Mean disease incidence was 72% across all the orchards evaluated, ranging from 43 to 100% in individual orchards. Disease severity ranged from 1.1–2.4 (mean =1.6) on a 0-4 scale. The most prevalent pathogens identified were Fusarium oxysporum, Fusarium proliferatum, Neoscytalidium dimidiatum and Neoscytalidium hyalinum, Valsa sordida, and Cladosporium oxysporum. All fungicides tested exhibited high efficacy in inhibiting radial mycelial growth of the tested fungal isolates. The mean EC50 values for Azoxystrobin, Pydiflumetofen, Difenoconazoleand Tebuconazole were 0.9, 0.07, 0.001, and 0.0003 mg a.i/ml, respectively. The EC50 values of the tested fungicides confirmed the high sensitivity of all tested fungal isolates to these fungicides. Overall, these findings suggest that the tested fungicides could serve as useful tools for managing stone fruit dieback and decline.