Efficacy of Calcium Salts on Controlling Phytophthora pistaciae, the Cause of Pistachio (Pistacia vera L.) Gummosis

Research in plant disease management focuses on developing safe methods for humans and the environment in order to prevent the entry of harmful chemicals in food. Simple inorganic salts have low cost and are safe enough to be used as pesticides. Phytophthora genus causes crown and root rot (gummosis) in crops and leads to great losses in some pistachio (Pistacia vera L.) production areas annually. In this study, the potential efficacy of different calcium salts with various concentrations on Phytophthora pistaciae control was examined. This was done to find out a safe way of material usage instead of synthetic pesticides. Samples from the crown of a pistachio tree, with gummosis, were cultured on lima bean agar to isolate and purify the pathogen. P. pistaciae identification was done using the PCR method with ITS4 and ITS6 primers. Pathogenicity of isolate was confirmed through tests on apples, pistachio branches, and pistachio seedlings. Different concentrations of seven calcium salts (chloride, nitrate, sulfate, oxide, hydroxide, phosphate, and carbonate) were applied which reduced mycelial growth and 3000ppm of calcium oxide inhibited it completely. Most of the salts reduced the number of sporangia, zoospores, and cyst germination percentage. Calcium oxide and calcium hydroxide also caused hyphae branching and deformation of some sporangia. The results suggested that some calcium salts, especially calcium oxide, could control the growth of P. pistaciae in vitro. Future in vivo studies are needed to examine whether calcium salts can reduce the disease severity and spread of the pathogen in the environment if those are sprinkled over the soil around the infested crown.