Inhibitory effect of various fungicides on mycelial growth of Alternaria alternata; cause of Alternaria leaf spot disease on Rosa Indica L. in Pakistan

Rosa indica L. (family: Rosaceae) is an important and widely grown plant in the floriculture industry. Alternaria leaf spot disease of rose was observed in rose plantation at College of Agriculture, University of Sargodha, Sargodha. The study was carried out to isolate and purify the pathogen, which was identified as Alternaria alternata. Additionally, in vitro efficacy of five fungicides; success, copper oxychloride, metalaxyl+mancozeb, topsin M and kumulus against A. alternata were tested by using food poisoning technique. Three concentrations (100, 200 and 300 ppm) of each fungicide were used. Mycelial growth after 3rd, 5th and 7th day was measured. All the fungicides significantly inhibited the mycelial growth of A. alternata. Among those, metalaxyl+mancozeb was the most effective as compared to others. Maximum inhibition was observed after 3rd (89%), 5th (91.6%) and 7th (93.3) day by metalaxyl+mancozeb followed by success 43.3%, 41.0% and 29.6% respectively. After 3rd and 5th day copper oxychloride was least effective with 19.6% and 9.6% mycelial inhibition respectively while after 7th day the minimum 4.3% mycelial inhibition was observed by topsin M instead of copper oxychloride. Therefore, A. alternata is responsible for alternaria leaf spot disease of rose and metalaxyl+mancozeb was found to be the most effective fungicide against A.alternata in vitro.