Buffalograss is a warm-season, dioecious grass species yielding burs, which are routinely used for field plantings. The pistillate plants bear the burs containing 1–5 caryopses. Isolated caryopses readily germinate, but caryopses contained within burs exhibit strong dormancy, suggesting that burs inhibit germination. Priming burs with low concentrations of potassium nitrate (KNO3) is used as an industry standard to improve germination. Seed dormancy and germination in many species are strongly influenced by endogenous hormone levels, principally abscisic acid (ABA) and gibberellic acid (GA). It follows that buffalograss seed dormancy might be induced or overcome by altering the ratio of ABA to GA. The objectives of this research were 1) to contrast the effects of priming with KNO3 or water on bur germination, 2) to study how these treatments affected hormone profiles, specifically the ABA/GA ratios in the burs, and 3) to quantify treatment effects on the water permeability of the burs. Hormone profiles were analyzed following four postharvest seed-soaking treatments (24-hour 0.05 m KNO3, 24-hour H2O, 48-hour 0.05 m KNO3, and 48-hour H2O). Water infiltration tests on nontreated, 24-hour H2O-treated, and 24-hour 0.05 m KNO3-treated seeds were also conducted. Inconclusive hormone profiling results did not support the hypothesis that KNO3 postharvest treatment raises GA levels to encourage germination. Instead, our data support changes in seed morphology following KNO3 postharvest seed treatments which alter water permeability of the seedcoat leading to increased germination.
Katherine Kreuser, William C. Kreuser, Gautam Sarath and Keenan L. Amundsen
William C. Kreuser and Frank S. Rossi
Petroleum-derived spray oils (PDSOs) have been used for pest management in horticulture and agronomy for over a century. Civitas™ is a new PDSO designed for use in the turfgrass industry. It is commonly mixed with low rates of pesticides to reduce the environmental impact and improve plant stress tolerance. Civitas can cause phytotoxicity, which has limited its acceptance by the turfgrass industry. Civitas is mixed with a green pigment called Harmonizer™ to sustain acceptable turfgrass color. A field study and a growth chamber study were designed to quantify phytotoxicity, understand the role of Harmonizer, and isolate the cause of Civitas-induced phytotoxicity. Civitas, Harmonizer, their combination (Two-Pack), and a water-only control were applied to a research putting surface in Ithaca, NY, during 2012 and 2013. Civitas and Harmonizer were applied every 2 weeks at the rates of 5.0 and 0.3 mL·m−2, respectively. Visual turfgrass quality rating and canopy temperature were quantified several times weekly. Civitas caused chlorosis and decline in visual quality during both years. Harmonizer masked chlorosis but did not prevent a drop in stand density during the second field season. Treatments were replicated on annual bluegrass (Poa annua L.) in a growth chamber experiment. Civitas did not increase electrolyte leakage or alter the composition of cuticle; however, there were signs of oil persistence on the leaves and stomata and evidence of reduced gas exchange. Chlorosis resulting from oil persistence and reduced gas exchange is consistent with chronic PDSO phytotoxicity. This research demonstrated the potential for phytotoxicity with high rates of Civitas. Lower application rates likely reduce the potential for phytotoxicity but may also minimize the pest control benefits associated with the product.