Determination of the efficacy of phosphite-based formulations against Phytophthora capsici, the causal agent of root and crown rot in peppers

Phytophthora blight caused by soil-borne P. capsici is one of the most important disease limiting pepper production in geenhouse and field around the world and in Turkey. The pathogen causes root, crown, stem and fruit rot diseases in pepper plants and hence serious economic losses. In this thesis study, first time phosphite formulations of potassium, copper, manganese, zinc, ammonnium and urea was developed and produced. The phosphite products were tested at the doses of 100 (0,45 g/L), 200 (0,9 g/L), 400 (1,8 g/L) and 600 mL (2,7 g/L)/100 L water or acre to determine their effects on the mycelial development of P. capsici and on the root and crown rot disease in laboratory (in vitro) petri plate and controlled gowth room (in vivo) pot assays. In the laboratory assays, all phosphites prevented mycelial development and sporulation of P. capsici at 400 and 600 mL doses. Copper, zinc and ammonnium phosphites were the most effective products at these doses. These 3 phosphites decreased the mycelial gowth of the pathogen tremendously at 200 mL doses. Zink phosphite even reduced the mycelium gowth significantly at 100 mL doses. In the growth room assays potassium, manganese and zinc phosphite at 200, 400, 600 mL, copper and ammonnium phosphite at 400 mL and urea phostphite at 600 mL were found to be over 80 % effective against P. capsici. Copper phosphite at 200 and 600 mL doses and urea phosphite at 400 mL doses were around 75 % effective. Ammonnium phosphite and ürea phosphite were effective %68 and 55 % respectively at 200 mL doses. These results indicate that the phosphite formulations developed here have potential as new and efficient materials that could be used to control P. capsici in pepper production. The study also suggests that the phosphites other than potassium phosphite may be used as soil and foliar applications starting at the seedling stage to control P. capsici and other Oomycetes pathogens in pepper and other vegetables.