Author : Travis Russell
Publisher :
Page : 0 pages
File Size : 40,98 MB
Release : 2022
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ISBN :
Turfgrass diseases incited by Pythium spp. are diverse in their pathogenicity, preferred host range, etiology, epidemiology, and environmental parameters that encourage their development. Beginning in the mid-2000's, several instances were reported in the northeast United States of unique disease outbreaks being caused by unidentified Pythium spp. on annual bluegrass (ABG; Poa annua L.). The symptoms of the disease were not associated with other previously characterized Pythium turfgrass diseases such as Pythium foliar blight, Pythium root rot, and Pythium root dysfunction. This disease often affected ABG in mixed species putting greens containing creeping bentgrass (CBG; Agrostis stolonifera L.), and CBG appeared to not be a host of the disease. Symptoms on ABG appeared as 0.1 to 0.6 m diameter patches and individual leaves appear blighted and chlorotic with the border of the patch having a yellow/orange halo. The disease emerged during periods of warm and humid weather and further patch expansion was limited during outbreaks. Foundational understanding on the biology, etiology, and control of this disease referred to as Pythium patch remain unknown and warrant further investigation. Therefore, the objectives of this research were to 1) identify the causal agent of Pythium patch disease on ABG; 2) characterize the pathogenicity of Pythium arrhenomanes and Pythium aristosporum on ABG and CBG; and 3) investigate fungicidal control options for Pythium patch disease. Sixteen Pythium isolates obtained from symptomatic ABG were characterized morphologically and DNA sequencing was used to identify these isolates to the species level. Cardinal temperatures for growth of all isolates ranged between 25 and 35°C. Isolates produced inflated lobulate sporangia, diclinous antheridia averaging 5.3 antheridia per oogonium, and oogonia that were terminal, smooth-walled, and averaged 27.1 [mu]m. These morphological iv characters compared to taxonomic keys are in alignment with descriptions of Pythium aristosporum and/or Pythium arrhenomanes. Sequencing of the internal transcribed spacer region, the cytochrome oxidase subunits 1 and 2, and the ß-tubulin gene loci revealed phylogenies placing the isolates within the P. aristosporum-P. arrhenomanes cryptic species complex. Pathogenicity assays in controlled environment and field-inoculated settings were conducted with the isolates to confirm pathogenicity and evaluate pathogen aggressiveness. Controlled environment assays demonstrated the pathogenic nature of P. aristosporum-P. arrhenomanes on immature ABG. Field-inoculation experiments on an ABG putting green reproduced symptoms similar to natural outbreaks of the disease. Isolations from natural outbreaks and field-inoculation experiments recovered the causal pathogen most frequently from turfgrass crowns and leaves, and rarely from roots. Pythium aristosporum-P. arrhenomanes isolates were evaluated in vitro for fungicide sensitivity and a field experiment was conducted on Pythium aristosporum-P. arrhenomanes-inoculated ABG to evaluate disease control with fungicides. Most isolates were sensitive in vitro to cyazofamid, etridiazole, fosetyl-Al, mefenoxam, and potassium phosphite, but not to propamocarb and pyraclostrobin. Field experiments did not reveal differences between fungicide treatments and the nontreated control, and further research is needed to confirm fungicide efficacy for Pythium patch control in a field setting. This research improves our understanding of the biology, etiology, and chemical control of Pythium patch disease of ABG and confirms P. aristosporum-P. arrhenomanes as the causal agents. Further research should provide additional insights into this emerging disease so turfgrass managers can successfully prevent and control Pythium patch on ABG putting greens.