Rasmussen, S. L., and Stanghellini, M. E. 1988. Effect of salinity stress on development of Pythium blight in Agrostis palustris. Phytopathology 78:1495-1497. Salinity stress predisposed cultivar Penncross creeping bentgrass to inoculated plants at an Ec level of 0.5 ds/m. Increased salinity levels cottony blight caused by Pythium aphanidermatum at two temperature apparently affected the bentgrass rather than P. aphanidermatum. regimes. At 25-32 C, complete necrosis of all inoculated plants occurred at Mycelial growth rate of the fungus was increased only slightly by salinity electrical conductivity (Ec) levels of 4.3-7.1 decisiemens (ds) per meter in 2 levels up to 7.1 ds/ m. Zoospore production of P. aphanidermatum and two days, whereas at Ec levels of 0.5-2.8 ds/ m, death occurred within 3 days. At other species of Pythium decreased with increasing salinity levels up to 7.1 25-27 C, complete necrosis of all inoculated plants occurred at Ec levels of ds/m; production was completely inhibited at 14.2 ds/m. 4.3-7.1 ds/ m within a period of 5 days; no death was observed in control or Additional keywords: Pythium catenulatum, Pythium dissotocum. Penncross creeping bentgrass (Agrostis palustris Huds. amended with a NaCl and CaC1 2 solution 1:1 (w/w) to achieve 'Penncross'), a temperate region grass, is widely used throughout electrical conductivity (Ec) levels of 1.4, 2.8, 4.3, 5.7, 7.1, 14.2, and the world for golf course greens, tees, and fairways. Extensive 28.4 decisiemens (ds) per meter (1 ds/m = 640 ppm). The same development of resorts and recreational facilities has expanded the medium (0.5 ds/m) without the addition of salt was used as a use of Penncross bentgrass into tropical, arid, and semi-arid control. Cultures were incubated at 15, 20, 25, and 30 C, and, after climatic regions where nonpotable and saline water commonly are an initial growth period of 12 hr, the radius of each colony was used for irrigation, measured after 24 and 48 hr. There were two replicates of each The sensitivity of Penncross bentgrass to salinity has been salinity value at each temperature regime, and the experiment was documented (15); however, no studies have been conducted conducted three times. regarding the effect of increased salinity on the diseases commonly Effect of salinity on zoospore production. A 9-mm-diameter occurring on Penncross. Cottony blight, caused primarily by disk was cut from a 5-day-old VJA culture of each fungus and Pythium aphanidermatum (Edson) Fitz., is a particularly placed in a 9-cm-diameter petri dish containing 20 ml of NaCl and devastating disease on Penncross bentgrass. Environmental CaCI2 solution 1:1 (w/w) with Ec values of 1.4, 2.8, 4.3, 5.7, 7.1, conditions conducive for disease development include high relative and 14.2 ds/ m. Sterile distilled water was used as a control. After humidity, saturated soils, and daytime temperatures of 30 C or 48 hr incubation at 25 C, all zoospores had encysted and settled to greater (11). The accumulation of salts due to saline irrigation the bottom of the dish. Then 0.1 ml of 10% acid fuchsin was added water may impose an environmental stress leading to increased to each dish to stain the cysts. The total number of zoospore cysts plant susceptibility. Increased disease severity resulting from per plate was determined by counting cysts in 10, 0.5 mm 2 fungicide and herbicide use (6,14), and susceptibility of bentgrass arbitrarily selected sites on the bottom of the dish under a to Curvularia lunata from heat and leaf clipping stress (10), have compound microscope. The total number of cysts per dish was been reported. then calculated by multiplying the mean of the 10 sites by the The objective ofthis study was to determine the in vitro effect of surface area of the bottom of the dish (6,361 mm 2 ) and then more...