Recycling irrigation reservoirs (RIRs) are an emerging aquatic ecosystem and water resource of global significance. This study investigated the vertical distribution of water temperature, dissolved oxygen (DO), and pH in eight RIRs at two nurseries each in Virginia and Maryland from 2011 to 2014. Monomictic thermal stratification was observed from April to October in all RIRs, despite their shallow depths (0.75-3.89 m). The strongest stratification had a top-bottom temperature difference of 21.53°C. The top-bottom temperature difference was positively correlated with water column depth, air temperature, and daily light integral (p < 0.05). Wind speed did not impact the thermal stratification, likely due to their relatively small surface areas. Thermal stratification affected the vertical distribution of DO and pH. The top-bottom differences in DO and pH were greater during stratification periods than nonstratification periods. Water pH in all RIRs was higher at the top than at the bottom with the greatest difference of 4.16 units. Discovery and characterization of thermal stratification in RIRs helps understand water quality dynamics in this novel ecosystem and promote safe and productive water reuse for irrigation. Specifically, water withdrawal depths should be adjusted according to variations in temperature, DO, and pH during the stratification and nonstratification periods to mitigate pathogen risk and improve water treatment efficacy and crop production.(KEY TERMS: recycling irrigation reservoir; thermal stratification; recycled water quality; dissolved oxygen; pH; water management.)

Transmission electron microscopy was used to study the penetration and infection of pansy roots by Thielaviopsis basicola. Events observed in 7- to 10-day-old roots produced on moist filter paper differed slightly from those in roots from 4-week-old plants washed free of potting media prior to inoculation. By 3 h postinoculation (PI), epidermal cells of roots produced on filter paper exhibited aggregated cytoplasm and papilla formation in response to germ tube tips. The presence of callose in papillae was demonstrated using immunogold labeling. Papilla formation was not effective in preventing host cell penetration. A slender infection hypha emerged from a germ tube tip and grew through a papilla. Its tip then expanded to form a globose infection vesicle. By 6 h PI, infection hyphae emerged from infection vesicles, and invaded host cells showed signs of necrosis. By 8 h PI, infection hyphae had grown into cortical cells in spite of papilla formation in these cells. By 24 h PI, distinctive intracellular hyphae were present in necrotic cortical cells. In washed roots, most epidermal cells failed to respond to invasion. Hyphae simply grew through these cells and contacted cortical cells that exhibited aggregated cytoplasm and papillae formation. Infection structures similar to those produced in epidermal cells from roots grown on filter paper then formed in cortical cells of washed roots. The fact that T. basicola formed infection structures only in cells that responded to invasion suggests that T. basicola has a more complex relationship with its host than would be expected in a nectrotrophic pathogen. We believe that T. basicola is best described as a necrotrophic hemibiotroph.

Rhizoctonia web blight, caused by binucleate Rhizoctonia spp., is an annual problem in the southern United States on container-grown azaleas (Rhododendron spp.) that receive daily irrigation. Disease progress was assessed weekly from mid-May to mid-September on nursery-grown plants at three locations in Mississippi and Alabama in 2006, 2007, and 2008. Disease onset, defined as the appearance of blighted leaves at the exterior canopy of at least one plant, occurred on average on 20 July, and calendar date was a more precise predictor of disease onset than several combined time–weather variables. Disease progress curves exhibited weekly fluctuations around a typically exponential increase in the mean number of symptomatic leaves per plant until early to mid-September, after which web blight severity leveled off or declined due to disease-induced leaf dehiscence and the appearance of new, asymptomatic leaves. Based on the relative increase in the log-transformed number of infected leaves per plant, weekly assessment periods were classified as having slow (≤0%), intermediate (>0 to <10%), or rapid (≥10% increase) disease progress. Three-day moving averages (MA) of various weather variables were calculated, and lagged values (by 5 days) of the MA were used in an attempt to predict disease progress as slow, intermediate, or rapid. Of the periods assessed as having slow disease progress in the 2006–2007 data set (model development data), 90.6% (29 of 32) met at least one of the following heuristically derived criteria for the lagged MA: min. temperature < 20.0°C, max. temperature > 35.0°C, avg. vapor pressure deficit < 2.50 hPa, or day of the year > 240 (28 August). One or more of these same criteria were met in 5 of 16 (31.2%) assessment periods with rapid disease progress, indicating that periods with slow versus rapid disease progression could be distinguished reasonably well based on weather. Results were similar for the 2008 validation data. However, weather variables were not useful in separating periods with either slow or rapid disease progress from those having intermediate progress. Instead, weather variables were most useful when used in a negative-prognosis approach to predict disease progression as being “not rapid” (which includes slow and intermediate periods) or “not slow” (including intermediate and rapid periods). The data set was further analyzed using Classification and Regression Tree (CART) analysis to relate weekly disease progress periods to weather variables. The resulting CART model agreed with the heuristic approach in that temperature variables were more prominent than moisture variables in classifying disease progress periods. With both approaches, satisfactory accuracy was accomplished only with negative-prognoses that classified disease progress periods as not rapid or not slow based on temperature and moisture limits.

Web blight on containerized azalea is an annual problem for commercial nurseries during summer months in the southern United States. Losses to web blight are associated with the cost of fungicide applications, delayed marketing of diseased plants, and plant death. Two hundred and eleven isolates of binucleate Rhizoctonia were recovered from azalea leaves with web blight symptoms from two nurseries in Mississippi and Alabama over 3 years. The internal transcribed spacer region (ITS) of the ribosomal DNA (rDNA) was sequenced from all isolates to determine genetic identity. A single anastomosis group (AG) of binucleate Rhizoctonia represented 92% of the samples collected from infected leaves. Genetic data and hyphal fusion experiments confirmed that these isolates belong to AG-U, which was recently identified from root and stem infections on miniature rose in Japan. Isolates of binucleate Rhizoctonia belonging to anastomosis groups AG-R, CAG-7 (=AG-S), and AG-G were also identified in the sample in low frequency. This is the first report of the occurrence of binucleate Rhizoctonia AG-U in the United States.