Salt stress causes worldwide reductions in agricultural yields, a problem that is exacerbated by the depletion of global freshwater reserves and the use of contaminated or recycled water (i.e. effluent water). Additionally, salt stress can occur as cultivated areas are subjected to frequent rounds of irrigation followed by periods of moderate to severe evapotranspiration, which can result in the heterogeneous aggregation of salts in agricultural soils. Our understanding of the later stages of salt stress and the mechanisms by which salt is transported out of cells and roots has greatly improved over the last decade. The precise mechanisms by which plant roots perceive salt stress and translate this perception into adaptive, directional growth away from increased salt concentrations (i.e. halotropism), however, are not well understood. Here, we provide a review of the current knowledge surrounding the early responses to salt stress and the initiation of halotropism, including lipid signaling, protein phosphorylation cascades, and changes in auxin metabolism and/or transport. Current models of halotropism have focused on the role of PIN2- and PIN1-mediated auxin efflux in initiating and controlling halotropism. Recent studies, however, suggest that additional factors such as ABCB transporters, protein phosphatase 2A activity, and auxin metabolism should be included in the model of halotropic growth.
Pigments and phenolics that absorb ultraviolet light (UV) are involved in the protection of the photosynthetic apparatus during periods of high ultraviolet‐B (UV‐B) radiation and can be of benefit to turfgrasses. This study initiated in October 2010 and repeated in March 2011 aimed to characterize protective pigment responses to elevated UV‐B in cool‐season turfgrass. Tall fescue (Festuca arundinacea Schreb.), perennial ryegrass (Lolium perenne L.), and creeping bentgrass (Agrostis stolonifera L.) cultivars L93 and Penncross were tested. Turfgrass pigment responses were measured over a 1‐wk period during which they were subjected to 16 kJ m−2 d−1 of UV‐B in growth chambers. Photoperiod was 14 h and plants were subjected to 26.2 mol m−2 d−1 photosynthetically active radiation (PAR) at 20° C day and 17°C night. Turfgrass samples were collected at Day 0, 1, 3, 5, and 7. Measurements included chlorophyll fluorescence, chlorophyll pigmentation, and flavonoid, phenolic, anthocyanins, and carotenoid concentrations. Chlorophyll fluorescence increased and chlorophyll quantities decreased significantly (P < 0.05) in UV‐B conditions compared to control. All species had significantly (P < 0.05) higher quantities of total phenolics and flavonoids at the top of the tissue canopy relative to roots and shoot tissue near the soil surface. Anthocyanins were only found in creeping bentgrass L93. Carotenoids, zeaxanthin, and β‐carotene declined in the UV‐B treatment for both creeping bentgrass L‐93 and Penncross after 7 d, but did not decrease for perennial ryegrass or tall fescue. Carotenoids may play a greater role in UV‐B tolerance than anthocyanins in cool‐season turfgrasses due to their ubiquitous presence.
Fine fescues, taxa within the Festuca genus, are considered some of the most shade‐tolerant cool‐season turfgrasses, but past research from field studies has been inconsistent. The objective of this research was to evaluate variation in Chewings fescue (Festuca rubra L. ssp. commutata Gaudin, CH), hard fescue (F. brevipila Tracey, HD), and strong creeping red fescue (F. rubra ssp. rubra Gaudin, ST) morphology and physiology under simulated foliar shade and full sun. Experiments were carried out using 12 CH, 13 HD, and 15 ST entries within a greenhouse with or without a photoselective filter to simulate foliar shade. The filter reduced the red to far‐red (R/FR) ratio to ∼0.66, and light intensity was reduced to 30% of full sun under shade treatment. Several parameters were assessed including height, the number of tillers, biomass, total chlorophyll, and the chlorophyll a/b ratio. In both sun and shade experiments, ST were significantly taller than the other taxa. Chewings fescue and HD had significantly more tillers than ST in sun, but both CH and ST had significantly more tillers than HD in shade. Hard fescue had the greatest biomass in sun, and the least in shade. Significantly more CH genotypes lacked shade avoidance responses (SAR) than both other taxa under shade, and a greater proportion of HD were shade intolerant. Based on this study, CH > ST > HD in terms of improved response to shade. However, variation for response to shade observed within entries indicates potential for future improvement.
rubra taxa are more crabgrass suppressive than F. ovina. 2. There is large variability in weed suppression across entries within each fine fescue taxon. 3. Opportunities exist for plant breeders to develop new weed suppressive cultivars. 4. Future studies should aim to separate allelopathic effects from plant competition. Field evaluation of weed suppression in fine fescue (Festuca spp.
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