Growth regulation and abiotic stress tolerance in annual bluegrass (Poa annua L.)
Creators: name: McBride, Sean Patrick
Publisher: name: No Publisher Supplied
Year: 2024

description: Annual bluegrass (Poa annua L.) is a cool-season grass species distributed worldwide. Its ability to persist under low mow heights and intensive management practices allow P. annua to serve as a desirable turfgrass for putting greens in mild climates. However, its low tolerance to heat and drought stress diminishes P. annua performance during summer in transitional and temperate climates. Under such circumstances, P. annua decline results in undesirable putting greens, especially in stands that commonly exist mixed with creeping bentgrass (Agrostis stolonifera L.). It is for this reason that P. annua is typically considered a problematic weed. However, control is often difficult and golf course superintendents may opt to cultivate P. annua despite its low summer stress tolerance. This requires high external inputs during summer months to maintain acceptable levels of play. Despite being consistently ranked as having poor heat and drought tolerance compared to other cool-season grass species, little is known regarding the mechanisms governing P. annua inferior resistance. The objectives of this research were to test the application of different products on improving P. annua summer performance and provide insight into the mechanisms governing P. annua low heat and drought stress tolerance. The first experiment was conducted over a two-year period at one location in New Jersey, on adjacent field plots. The study evaluated the effectiveness of several fungicides alone and in combination with a plant growth regulator for a total of 4 treatment programs [Daconil Action (chlorothalonil and acibenzolar-S-methyl); Appear II (Potassium phosphite); Daconil Action + Appear II; Daconil Action + Appear II + Primo Maxx (trinexapac-ethyl)] on improving P. annua summer performance. Treatments were applied every two weeks from June through September on P. annua managed under putting green conditions. Results indicated the ability of the fungicide treatments alone (Daconil Action or Appear II) or in combination (Daconil Action + Appear II or Daconil Action + Appear II + Primo Maxx) to improve P. annua summer performance to varying degrees; with the combination treatments having more consistent and greater effects. Two additional studies were conducted in growth chambers to gain insight into the mechanisms governing P. annua low heat and drought stress tolerance. One compared P. annua response to heat stress to the relatively more tolerant A. stolonifera, while the second compared their differential response under drought stress followed by post-drought recovery. Physiological parameters and metabolic analysis were conducted, and interspecific differences were observed between P. annua and A. stolonifera. Under heat stress P. annua exhibited more severe stress than A. stolonifera paired with the following metabolic differences: a relatively lower accumulation of sugars, such as sucrose, and a greater decline in organic acids and carbon intermediates that serve as substrates in photosynthesis, respiration, secondary metabolism, and stress protection. Under drought stress, P. annua exhibited greater signs of stress followed by slower recovery upon rewatering compared to A. stolonifera. Its lower drought resistance and slower recovery were associated with an inferior accumulation of metabolites (sugars and amino acids, such as sucrose, proline, and GABA) that can serve as osmolytes, have antioxidant properties, and can be metabolized upon rewatering to facilitate faster recovery. A third growth chamber study was conducted to test the ability of two ethylene inhibitors to improve P. annua tolerance to heat stress. The treatments included a chemical inhibitor, aminoethoxyvinylglycine (AVG), and a biological ethylene inhibitor, Paraburkholderia aspalathi, a plant growth-promoting rhizobacteria (PGPR) with 1-aminocyclopropane-1-carboxylic acid deaminase (ACCd) activity. After 21 days of heat stress both ethylene inhibitors improved P. annua performance under heat stress, indicated by higher turf quality, green canopy cover, relative water content, chlorophyl content. Both treatments also improved P. annua root maintenance under heat stress, where AVG had significantly greater root dry weight (g), while the PGPR with ACCd activity resulted in greater root total length (cm). Overall, results provided evidence that fungicides and plant growth regulators can improve P. annua summer performance, in the absence of disease. Additionally, key metabolites were identified giving insight into the pathways involved in P. annua susceptibility to heat and drought stress. Lastly, ethylene inhibitors were identified as a possible strategy for improve P. annua performance under heat stress.