Anthracnose caused by Colletotrichum gloeosporioides is one of the predominant postharvest diseases of rambutan in Sri Lanka. In this study, the in vitro potential of two selected T. harzianum isolates (R1 and R2) was evaluated against the postharvest anthracnose pathogen (C. gloeosporioides) of rambutan (Nephelium lappacium L.). Two T. harzianum isolates (R1 and R2) isolated from soil samples in rambutan orchards had antagonistic effects against the pathogen. In-vitro potential of R1 and R2 isolates were tested using dual culture method, well diffusion method and filter paper disc-agar diffusion method to determine the antagonistic effect.
Of these two isolates R2 exhibited the greatest (89.76%) and significant (P < 0.05) inhibition of pathogen in dual culture method. Microscopic investigation demonstrated direct parasitism and coiling of two isolates around the hyphae of the pathogen, causing swollen, deformed, shortened or rounded cells of the pathogen. Granulation of cytoplasm, cellular coagulation and cell wall disintegration of hyphal cell walls of the pathogen were also noted in the slide culture. Further, significantly inhibitory effect was observed in R2 than in R1.
In well diffusion method carried out at different concentrations of the spore suspension of antagonists, two T. harzianum isolates exhibited a significant, synergistic effect on suppression of growth of pathogen when they applied in 1:1 ratio than applying each of them alone. Furthermore, the crude culture filtrates of both isolates showed an antifungal effect on pathogen expansion and conidial germination in vitro. The greatest antifungal effect in disc-diffusion method and the highest percentage inhibition of germination of conidia (49.07%) were observed when C. gloeosporioides challenged with the crude culture filtrate of R2 isolate.
Between two Trichoderma isolates though the antagonistic activity is due to both mycoparasitism and antibiosis, R2 showed the greatest inhibitory effect in all experiments than R1. Thus, R2 isolate can be suggested as a better biological control agent to control the postharvest anthracnose disease of rambutan and also further studies should carry out to investigate the synergistic inhibitory action of both isolates in control of postharvest diseases.
Key Words:- Trichoderma harzianum, Anthracnose, Colletotrichum gloeosporioides,
Rambutan (Nephelium lappacium L.), Antagonism, Biological control.
I.U.Kariyawasam1, K.M.E.P. Fernando1, R.S. Wilson Wijeratnam 2.
1. Department of Botany, University of Sri Jayewardenepura, Nuggegoda.
2. Food Technology Division, Industrial Technology Institute, Colombo 7.