Morphological, Molecular Identification and Pathogenicity of Neoscytalidium dimidiatum Causing Stem Canker of Hylocereus polyrhizus in Southern Thailand

Abstract

Red-fleshed dragon fruit (Hylocereus polyrhizus) is commonly cultivated in Thailand, especially in southern Thailand, where the weather favors plant growth and development. In 2021, stem canker of H. polyrhizus was observed in a dragon fruit plantation field in Phatthalung Province, southern Thailand. Small, orange circular spots developed on the stem of H. polyrhizus, which later became gray, and the lesion expanded with a mass of conidia. Scytalidium-like fungus was isolated from infected tissues. Based on morphology and phylogenetic analyses of internal transcribed spacer (ITS), nuclear large subunit (LSU) and β-tubulin (tub) sequences of fungal isolates, the fungus was identified as Neoscytalidium dimidiatum. Pathogenicity tests revealed that this isolate caused stem canker on the stem of H. polyrhizus, similar to that observed in the field. Knowledge of the diagnosis of plant diseases is an important step for managing plant diseases and therefore, this finding provides basic information for the development of appropriate strategies to manage stem canker disease on H. polyrhizus plants.

A New Species of Neoscytalidium hylocereum sp. nov. Causing Canker on Red-Fleshed Dragon Fruit (Hylocereus polyrhizus) in Southern Thailand

“…Stem canker in dragon fruit has been recognized to be caused by the fungus N. dimidiatum throughout Asian countries [ 10 , 14 ]; however, very few reports exist regarding the life cycle in dragon fruit. Infected dragon fruit shows three stages of symptoms, including sunken yellow to orange flecks, the raising up of the infected site due to tissue proliferation beneath the infected area and pycnidia forming on the surface of dragon fruit cladodes, which was observed in a new species, N. hylocereum , in this study.…”

“…Recently, flower rot of red-fleshed dragon fruit was reported to be caused by the fungus Gilbertella persicaria in southern Thailand [ 13 ]. Dy et al [ 14 ] also demonstrated that the fungus N. dimidiatum acted as a pathogen, causing stem canker in H. polyrhizus in southern Thailand.…”

Morphological and Molecular Characterization of Calonectria foliicola Associated with Leaf Blight on Rubber Tree (Hevea brasiliensis) in Thailand

“…A total of 10 symptomatic Calonectria -like leaf samples were collected in plastic bags, kept in a cooler box, and brought to the Plant Pathology Laboratory, where isolation was subsequently conducted. Fungi were isolated from symptomatic leaves using a tissue transplanting method [ 27 , 28 ] with some modifications. Small pieces (3 mm × 3 mm) of symptomatic tissues containing healthy tissues were cut using a razor blade, surface disinfected using 0.5% sodium hypochlorite (NaOCl) [ 29 ] and rinsed with sterile distilled water (DW).…”

Pest categorisation of Neoscytalidium dimidiatum

“…N. dimidiatum can be readily isolated on culture media and description of its cultural and morphological characteristics is available in the literature (Crous et al., 2006 , 2021 ; Nouri et al., 2018 ; Zhang et al., 2021 ; Dy et al., 2022 ) (Figure 1 ). In the past, the identification of species of the family Botryosphaeriaceae, including N. dimidiatum , was based on cultural and morphological characteristics, resulting in many cases to misidentifications since conidial septation and pigmentation evolved more than once within different genera and are strongly influenced by the cultural conditions (Slippers et al., 2013 ).…”

“… Morphological characteristics of Neoscytalidium dimidiatum on Hylocereus polyrhizus : (a) & (b) 3‐day‐old colony on PDA in top and bottom view, respectively, (c) 4‐week‐old colony on PDA developed small black conidiomata (arrow), (d) zoom view of conidiomata, (e) hyphae and phragmospores (arthroconidia), (f) pycnidia developed on dried Napier grasses, (g) conidiogenous cells and (h) conidia (pycnidiospores (from Dy et al., 2022 ) …”