Etiological Study of Black Spot Disease on Rose Leaves From Kota Samarahan, Sarawak

Rose (Rosa sp.) is an ornamental plant of choice for home gardening, landscaping and commercial growing for many years. Unfortunately, several prevalent diseases including the black spot disease have been devastating the health, aesthetic value and its marketability. Hence, before an efficient control method can be applied to overcome the problems, this study aims to identify the etiological agent on the black spot disease on rose leaf by means of Koch’s Postulate. Isolated pathogens from infected rose leaves were inoculated via in vitro leaf inoculation and shoot inoculation. Infected leaves were then re-isolated and identified the etiological agent using slide culture method. Further fungicide test was done on the growth of the fungal pathogen by utilizing chemical fungicide. A total of 25 isolates were completely used as inoculum source to infect the young rose leaves. However, only 1 isolate was showed the black spot symptom at the end of the both inoculation experiments. Since the reproductive structures developed in 2 different representative species, which are Uncinula sp. in teleomorph and Marssonina rosae in anamorph, these have made the study unable to determine the actual causal agent of black spot disease on rose leaf. Thus, further research need to be carried out to investigate the presence of mixed pathogens on the disease. Nevertheless, both of the causal agents gradually reduced in their length of colony growth when chemical fungicide was applied