Dissimilatory Reduction of Sulfate in Black Layer

Black layer has been associated with a severe decline in the quality of turf on putting greens. It was suggested that the black layer results from dissimilatory sulfate (SO42–) reduction. This study was done to determine if SO42– reduction occurs in an existing black layer. Radioactive 35SO42– was used to calculate the rate of SO42– reduction in intact soil cores taken from an existing black layer in a `Penncross' creeping bentgrass (Agrostis palustris Huds. `Penncross') putting green. When 10–3 M 35SO42– with a specific activity of 1.554 × 105 Bq·mg–1 SO42– was injected into a core it reduced to sulfide (35S2–) at a mean rate of 7.1 nmol sulfur (S)/cm3 soil/d. Injecting azide (N3–) or molybdate (MoO42–) at 10% w/v with the label reduced the rate of SO42– reduction to 0.03 and 0.01 nmol S/cm3 soil/d, respectively. The effect of N3– confirmed that reduction of SO42– was biological, while the effect of MoO42– confirmed that the entities responsible for the reductive cycling were sulfate-reducing bacteria (SRBs). This was the first proof that biological reduction of SO42– produces S2– in a black layer from a creeping bentgrass putting green. It was concluded that the respiration of indigenous SRBs was linked to development of this black layer. Thus, a key to successfully controlling black layer in putting greens must involve regulating the respiratory activities of SRBs.

Variable adhesion and diurnal population patterns of epiphytic yeasts on creeping bentgrass

Irrigation and an in vitro agitation assay were used to determine the percentage of the epiphytic yeast community (Cryptococcus, Pseudozyma, Rhodotorula, and Sporobolomyces) adhering to the phylloplane of creeping bentgrass (Agrostis palustris (Huds.) Pers.). Colony-forming units (cfu) of total epiphytic yeast populations (adherent and nonadherent cells) and of adherent populations (cells not removed by agitation) were determined by leaf washing and dilution plating. In an in vitro assay, 40.0% and 57.1% of the yeast adhered to the leaves, whereas, in initial field trials the percentage of adherent yeasts ranged from 40.0% to 71.9% of the total population. Adherent yeast cfu on leaves in the morning were significantly lower on bentgrass (8.0 × 103to 3.1 × 104cfu·cm–2) compared with total yeast cfu (1.4 × 104to 4.7 × 104cfu·cm–2) on the nonirrigated control. No differences in yeast populations were observed between irrigated and nonirrigated plots 2 h after the 0900 treatments. Yeast populations followed a diurnal pattern, with larger cfu recovered from bentgrass leaves in the morning and significantly lower populations recovered in the afternoon. At 1400 the adherent yeast were 83.1%–100% of the total yeast population recovered from the leaves. The relative adhesiveness of the epiphytic yeast community on bentgrass leaves is dynamic with nonadherent cells making up a larger percentage of the population in the mornings than the afternoons.Key words: adherence, Cryptococcus, leaf surface, Rhodotorula, turfgrass.

Response of Creeping Bentgrass to Salinity and Mowing Management: Carbohydrate Availability and Ion Accumulation

Salt problems in turfgrass sites are becoming more common. The effects of mowing height on salinity tolerance and associated mechanisms are not well understood. The objective of this study was to examine the effects of mowing height and the level of salinity on turf quality, canopy photosynthetic rate (Pn), total nonstructure carbohydrate (TNC) content, shoot reducing sugar content (RSC), Na+ and K+ content in shoots and roots of creeping bentgrass (Agrostis palustris Huds.). Sod pieces of `L-93' were grown in a greenhouse for over 7 months. Plants were subjected to three mowing heights: 6.4, 12.7, and 25.4 mm, and to four salinity levels of irrigation water: control, 5 dS·m–1, 10 dS·m–1, and 15 dS·m–1 prepared using ocean salts. Increasing salinity resulted in reduced turf quality, increased shoot Na+, reduced K+, and reduced K to Na ratio, to a greater extent for bentgrass mowed at 6.4 mm mowing height. Reducing sugar content in shoot increased with increasing salinity level except at 15 dS·m–1 and 6.4 mm mowing regime where RSC declined. Compared to the 25.4 mm mowing height, mowing height at 6.4 mm caused 32-39% reduction in TNC, a 25% to 37% increase in Na+ content, and 45% to 51% decrease in K content in shoots, which resulted in substantial decrease in K/Na ratio. These results demonstrated that the reduction of creeping bentgrass salt tolerance under low mowing height was associated with carbohydrate depletion that reduced the plant's genetic abilities to generate osmo-protectants (such as reducing sugar), to reduce Na+ accumulation in shoots, and to selectively uptake and transport K+. Therefore, a moderate increase in mowing height could improve salinity tolerance of creeping bentgrass.

Use of the growth regulator paclobutrazol in the management of dollar spot of creeping bentgrass in Minnesota

The control of dollar spot by paclobutrazol applied as a growth regulator on a creeping bentgrass (Agrostis palustris) and annual bluegrass (Poa annua) fairway turf was compared with two standard fungicide treatments in Minnesota during two growing seasons. Paclobutrazol was applied every 3 weeks, staggered by about 10 days with fungicide treatments (chlorothalonil or propiconazole), also applied every 3 weeks. Paclobutrazol alone significantly reduced the number of dollar spot infection centers during both summers, often by as much as 80%. Chlorothalonil or propiconazole were usually more effective in controlling dollar spot than paclobutrazol. Paclobutrazol improved disease control by fungicides when tested in combination with various rates of chlorothalonil or propiconazole. Paclobutrazol applied as a growth regulator could thus be used to reduce the base line severity of dollar spot of turf.