Archivio Journal of Plant Pathology

Abstract:

Common screw-pine (Pandanus utilis Bory) is a common ornamental tree in southwest China. Since April 2013, small and yellowish spots were observed on the leaf edge or base of common screw-pine grown in Yunnan Province, China. The lesions gradually increased in size and turned reddish-brown, then white and dry in the center but remaining reddish-brown at the margins. A fungus was consistently isolated from these lesions; on PDA, its macrospores were sickle-shaped, most 3 or 4 septate, 41 (40 to 42) x 4.2 (3.2 to 5.1) μm; microspores were fusiform or obovoid, 0 to 1 septate, 8.5 (5.8 to 10) × 4.0 (3.4 to 4.9) μm (n=50). Pathogenicity was confirmed by inoculating three leaves from each of three healthy adult plants with 60 μl of a conidial suspension (1 × 106 conidia/ml). Non-inoculated leaves were used as controls, all leaves were covered with a plastic bag and incubated indoor at 20 to 29°C and relative humidity of 64 to 83%. Symptoms similar to those observed in the field developed on inoculated leaves, while controls remained symptom free. The fungus could be re-isolated from symptomatic leaves but not from the controls. Its identity was further investigated by sequence comparison of the ITS (primers ITS1/ITS4), RPB2 (primers 5F/7CR) and TEF gene (primers EF1-728F/EF1-986R) of isolate SLYZ-2 (Summerell et al., 2003). BLASTn analysis of the ITS gene (KT459352) with cognate sequences available in the GenBank database revealed 99% sequence identity to Fusarium oxysporum but only 95.9% sequence identity to F. incarnatum-equiseti in the FUSARIUM-ID (http://isolate.fusariumdb.org) database. However, BLASTn analysis of the RPB2 (KX768542) and TEF gene (KX768543) revealed 99.66 and 100% sequence identity, respectively, to F. oxysporum in both GenBank and FUSARIUM-ID database. Therefore, both molecular and morphological observations indicated that the pathogenic fungus was F. oxysporum. F. oxysporum was reported to cause leaf twisting on Allium cepa var. ascalonicum in U.S.A. (Kuruppu, 1999) and leaf spot on Dracaena arborea cv. massangeana (Wu et al., 2015). To our knowledge, this is the first report of F. oxysporum on P. utilis from Yunnan, China as well as worldwide.