Susceptibility of the three dragon fruit species to stem canker and growth inhibition of Neoscytalidium dimidiatum by chemicals

Abstract

In the Philippines and other Southeast Asian countries, dragon fruits (Hylocereus species) have the potential to be a major “cash crop”. However, among the major problems currently faced by growers are yield- and quality-limiting diseases. In the Philippines, little is known of the dragon fruit diseases and measures that may be used in disease management. In this study, Neoscytalidium dimidiatum has been identified, by a combined morphological and molecular identification approach, as the cause of dragon fruit stem canker. The three dragon fruit species, H. monacanthus, H. undatus, and H. megalanthus, were susceptible to stem canker in both detached stems (3 laboratory trials) and rooted-stem cuttings (2 glasshouse trials) assays. The symptom was more severe in inoculated rooted-stem cuttings than in detached stems. Growth of N. dimidiatum was suppressed in potato dextrose agar (PDA) medium amended with B. subtilis (2 ml/400 mL, 100% fungal growth inhibition, fgi), mancozeb (2 g/400 mL, 100% fgi) and pyraclostrobin (1 mL/400 mL, 100% fgi) (chemical control). Citronella oil (1.25 uL/mL, up to 85.42% fgi) and isoprothiolane (2.25 mL/400 mL, up to 100% fgi) also showed promising results. However, the growth of N. dimidiatum was not inhibited in PDA medium amended with propamocarb (1.60 mL/400 mL). This is the first scientific report of N. dimidiatum as a pathogen of dragon fruit in the Philippines, the susceptibility of H. megalanthus to stem canker, and the growth inhibitory effect of B. subtilis and other chemicals that can be used alternatively or in rotation with synthetic chemicals.