Biological Control of Stem Canker in Red-Fleshed Dragon Fruit (Hylocereus polyrhizus) by Emulsion Formulation of Trichoderma asperelloides PSU-P1

Abstract

Stem canker of red-fleshed dragon fruit (Hylocereus polyrhizus) was observed on dragon fruit plantation field in Phatthalung province, southern Thailand. The disease samples were collected and isolated by tissue transplanting method. Pathogenicity was conducted on healthy cladodes of dragon fruits by agar plug method and revealed the fungal isolate PSU-SC02 caused stem canker on cladodes of H. polyrhizus. Fungal isolate PSU-SC02 was identified based on morphology and molecular properties of double DNA sequences of internal transcribed spacer (ITS) and β-tubulin (tub) as Neoscytalidium dimidiatum. Biological control by Trichoderma species are widely used to control several plant diseases. However, environmental conditions affect bio-control agent in the field, development of appropriate formulation is an alternative way to solve this problem. This research aimed to develop a new Trichoderma asperelloides PSU-P1 formulation that would be more effective against N. dimidiatum. Three vegetable oils, two emulsifier-dispersing agents (Tween 20 and Tween 80) and one source of carbon (dextrose) were tested for carrier additive. Viability and antifungal ability of formulation incubated at ambient temperature and at cool temperature (10oC) were compared. A total of 12 emulsions based was tested for viscosity by evaluating the mixing time. The formulation composed of coconut oil, DW and tween 20 in a ratio of 30:60:10, respectively, showed the great mixing time of 1.14 min significantly lower than that of other formulations (p<0.05). Application of this formulation suppressed canker development with 0.53 cm2 symptom area compared with control (pathogen alone) 1.65 cm2. Viability of T. asperelloides PSU-P1 conidia was observed by percentage of surface area in PDA plates at day 3, whereas percentage inhibition was observed on colony radii of N. dimidiatum. Viability of this formulation stored at ambient temperature showed percentage of surface area of T. asperelloides PSU-P1 ranged 58.08–100% whereas formulation stored at cool temperature showed 70.59–100%. This formulation effectively inhibited N. dimidiatum in PDA plates with percentage inhibition rage from 50–77% and 54.2–76.19%, respectively in the same manner with viability. This finding suggested that the emulsion formulation developed in this study was appropriated to store T. asperelloides PSU-P1 conidia with high viability and antifungal ability up to 6 months.