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  • Author or Editor: Joshua J. Blakeslee x
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Anthocyanins are plant pigments that are in demand for medicinal and industrial uses. However, anthocyanin production is limited due to the harvest potential of the species currently used as anthocyanin sources. Rough bluegrass (Poa trivialis L.) is a perennial turfgrass known for accumulating anthocyanins, and may have the potential to serve as a source of anthocyanins through artificial light treatments. The objectives of this research were to determine optimal light conditions that favor anthocyanin synthesis in rough bluegrass, and to determine the suitability of rough bluegrass as a source of anthocyanins. When exposed to high-intensity white light, rough bluegrass increased anthocyanin content by 100-fold on average, and anthocyanin contents greater than 0.2% of dry tissue weight were observed in some samples. Blue light, at intensities between 150 and 250 μmol·m−2·s−1, was the only wavelength that increased anthocyanin content. However, when red light was applied with blue light at 30% or 50% of the total light intensity, anthocyanin content was increased compared with blue light alone. Further experiments demonstrated that these results may be potentially due to a combination of photosynthetic and photoreceptor-mediated regulation. Rough bluegrass is an attractive anthocyanin production system, since leaf tissue can be harvested while preserving meristematic tissues that allow new leaves to rapidly grow; thereby allowing multiple harvests in a single growing season and greater anthocyanin yields.

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Creeping bentgrass (Agrostis stolonifera L.) is a turfgrass species that is widely used on golf courses throughout the United States. In field settings, plants are often subjected to more than one stress at a time, and studying stresses independently is likely insufficient. Stresses, such as heat stress and salt stress, can affect plant hormone levels and, in turn, plant hormone levels can affect how well the plant tolerates stress. The objectives of the experiments were to determine if the levels of heat stress and salt stress used would be detrimental to creeping bentgrass health, and if applying plant growth regulators could improve plant health during stress. During the first experiment, creeping bentgrass was transplanted to hydroponics systems in two different growth chambers. One chamber was set to have day and night temperatures of 35 °C and 30 °C (heat stress), respectively, and the other had day and night temperatures of 25 °C and 20 °C, respectively. Within each chamber, one block received a 50 mM NaCl treatment (salt stress) and the other did not (control). The stress treatments were applied for 14 days. Results of the first experiment indicated that the treatments were sufficient to negatively affect creeping bentgrass growth and health as indicated by fresh shoot and root weights, tillering, electrolyte leakage, and total chlorophyll content (TCC). There were significant interactions of temperature × salt level detected for shoot and root weights and electrolyte leakage. Plants that were exposed to both heat stress and salt stress were more negatively affected than plants exposed to either heat stress or salt stress alone for all metrics except for tillering. The presence of salt reduced tillering regardless of the temperature regimen. During the second experiment, plants were treated the same, but the plant growth regulator (PGR) treatments were also applied. The PGR treatments consisted of two different gibberellic acid (GA) synthesis inhibitor products, 2,4-dichlorophenoxyacetic acid, two different rates of aminoethoxyvinylglycine (AVG), an ethylene synthesis suppressor, and plants that were not treated with the PGR. In addition to the measurements of plant health and growth, dry shoot and root weights were measured. For the TCC, there was a two-way interaction between temperature × PGR treatment. For electrolyte leakage, there was a three-way interaction between temperature × salt level × PGR treatment. Combined heat stress and salt stress negatively affected all plants regardless of PGR treatment, but there were differences between PGR treatments. Plants treated with AVG exhibited improved health and growth compared with the other PGR treatments. These plants had the highest shoot and root masses. Plants treated with GA synthesis inhibitors had the lowest shoot and root masses as well as the lowest TCC when subjected to stress.

Open Access

Since the mid-1980s, a syndrome known as mature watermelon vine decline (MWVD) has had a serious effect on watermelon (Citrullus lanatus Thunb.) crops in Southern Indiana. As efforts to identify a pathogen responsible for MWVD have been unsuccessful, we have examined cultural conditions that might contribute to the syndrome. Field conditions were simulated in greenhouse pot trials to assess the impact of one or more factors on watermelon growth. Alone, low organic matter, soil acidity, black plastic mulch, and liming did not significantly affect root fresh weight; however, when these conditions were combined, root fresh weight was significantly reduced. Alanap-treated watermelons in combination with simulated cultural conditions resulted in further reduction of root fresh weight and had symptoms similar to MWVD. Watermelon plants grown in Alanap-treated, aged soil (from the previous year's experiments) under combined deficient cultural conditions demonstrated increased symptoms of MWVD and susceptibility to the pathogens Rhizoctonia and Pythium spp. Alanap, N-1-naphthylphthalamic acid (NPA), is a preemergent herbicide that functions as an inhibitor of auxin efflux and is widely used by watermelon farmers to impede obnoxious weeds. Metabolism of Alanap in planta involves aryl amidases (aminopeptidases) that also function in defense responses. We hypothesize that negative cultural practices are likely to inhibit defense responses and watermelon resistance to residual Alanap, leading to MWVD. We suggest that MWVD incidence is increased by certain common cultural conditions and that the incidence of MWVD can be reduced by altering these cultural practices.

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