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Daffodils [Narcissus sp. (L.) Amaryllidaceae] are popular landscaping plants and cut flowers. The daffodil cultivars ‘Dutch Master’, ‘Ice Follies’, and ‘Tete-a-Tete’ are considered highly tolerant to salinity by maintaining visual quality at NaCl induced electrical conductivity (EC) greater than 6 dS⋅ m−1. In geophytes, the bulb can act as a buffer for stress, and in this study we wanted to determine how the bulb contributes to salinity tolerance in these three daffodil cultivars. Bulbs were divided into three weight categories and exposed to irrigation salinities of 0, 50 and 100 mM NaCl during chilling, active growth and flowering. Regardless of the level of salinity exposure, plants (regardless of salinity or cultivar) with large bulbs grew at least twice the rate as plants from small bulbs grown at the same salinity. Flowers lasted on average 2 days longer in large bulb plants compared to small bulb plants. The ability to flower was impacted by cultivar and bulb size, with the least flowering occurring in small bulb ‘Dutch Master’ plants. In contrast, salinity was the main factor affecting leaf osmotic potential and relative water content (both decreased by 13%), antioxidant capacity (increased by 11%), gas exchange (reduced 50–75%), and cation uptake (5 fold increase in NaCl treatments). Although increasing bulb size did not improve all plant factors impacted by salinity, increases in initial bulb size improved overall growth at all levels of salinity and allowed the plants to maintain flower production and visual quality.

Evolutionary divergence among disjunct populations that encounter different stressful conditions may be rapid due to limited gene flow. Arabidopsis lyrata ssp. lyrata (L.) O’Kane & Al-Shehbaz grows throughout the mid-Atlantic region in a variety of fragmented and stressful environments, including serpentine soils. The purpose of this study was to investigate the differential responses to heavy metals (particularly nickel and chromium, naturally occurring in serpentine soils) among three serpentine populations compared to two non-serpentine populations of A. l. ssp. lyrata , as evidence of local adaptation. The five populations were exposed to a nickel, chromium or control treatment during germination and juvenile growth. None of the populations had a negative growth response to chromium. All five populations had reductions in growth when exposed to nickel. The greatest reductions were found in the two non-serpentine populations, which had reductions of 97–99% compared to the control. In contrast, the three serpentine populations had reductions of 23–83%, with most reduction in one of the serpentine populations (Robert E. Lee). Compared to the non-serpentine populations and the least tolerant serpentine population, the two most tolerant serpentine populations (Pilot and Soldiers Delight) had early lateral root formation, accumulated less nickel in their shoots and roots, and had high shoot phenolics. All three serpentine populations had increased serine levels in response to nickel and chromium. The tolerance mechanisms we found in the most tolerant serpentine populations serve as evidence for local adaptation to nickel stress in the non-hyperaccumulator A. l ssp. lyrata .

Salinity is a problem for crop production worldwide and may be particularly problematic for ornamental plants because it has the potential to degrade visual quality. Daffodils [Narcissus sp. (L.) Amaryllidaceae] are a popular bulb plant, in demand for both landscapes and cut flowers. In this study, we examined how salinities ranging from 0 to 300 mm NaCl affected growth, flower production, and leaf physiology of three of the most popular cultivars of daffodil (‘Dutch Master’, ‘Ice Follies’, and ‘Tete-a-Tete’). Salinity reduced growth rate and biomass production at salinities greater than or equal to 100 mm NaCl with the greatest reductions in the highest salinity treatments (200 and 300 mm NaCl). Despite reductions in biomass, there was no significant chlorosis of the leaves. Flower quantity was unaffected by salinity in ‘Dutch Master’ and ‘Ice Follies’, but anthesis was delayed and flower duration was reduced by 40% to 70% at salinities of 150 mm NaCl and above. Anthesis and flower duration in ‘Tete-a-Tete’ were unaffected by salinity, but the number of flowers produced was negatively affected (reductions of 50% or more) by salinities of 150 mm NaCl and above. Sodium concentration in the leaves and bulbs increased 53% to 400% compared with the 0 mm NaCl control with lower accumulation in the bulbs than in the shoots. Sodium accumulation occurred at or above 50 mm NaCl in ‘Tete-a-Tete’, but at salinities greater than 150 mm NaCl in ‘Dutch Master’ and only in the 300-mm NaCl treatment in ‘Ice Follies’. Despite the Na+ accumulation in the leaves, the plants in most of the salinity treatments were able to maintain a K+:Na+ ratio above 1 (except in ‘Tete-a-Tete’ at salinities 150 mm NaCl or greater), which may have helped the daffodils tolerate the negative affects of Na+ and maintain good visual quality. ‘Dutch Master’, ‘Tete-a-Tete’, and ‘Ice Follies’ can be considered highly salt-tolerant because they maintain visual quality (leaf greenness, flower production, and flower duration) at soil NaCl-induced electrical conductivities greater than 6 dS·m−1.

Salinity affects crop production worldwide and can be particularly problematic for ornamental plants. Daffodils (Narcissus sp. L.) are one of the most popular bulb plants, in demand for both landscapes and cut flowers. In this study we examined how moderate salinity, imposed as NaCl, affected growth, flower production, and leaf physiology when salinity treatment began either pre- or postemergence. Salinity did not affect growth rate or flower production for the three early-season cultivars (‘Dutch Master’, ‘Ice Follies’, and ‘Tete-a-Tete’) regardless of when salinity treatment began, but there were reductions in dry shoot biomass production under the highest salinity (50 mm NaCl). The mid-/late-season cultivar (‘Actaea’) had growth reduction and decreased flower production at the highest salinity when salinity treatment began preemergence. Within 28 days of greenhouse growth, the plants in the 50 mm NaCl treatment had carbon assimilation rates of only 25% to 32% of the 0 mm NaCl control. Sodium concentration increased 35% to 900% in the leaves in response to salinity for all cultivars when salinity treatment began preemergence but significantly increased only for ‘Actaea’ and ‘Tete-a-Tete’ (42% to 235%) when salinity treatment began postemergence. Potassium concentration in the shoot was mostly stable in response to salinity. The ability to maintain potassium (K) content within the plant may help daffodils tolerate the negative effects of sodium (Na). We believe that ‘Actaea’ was more negatively affected by salinity than the other three cultivars because, as a mid-/late-season cultivar, it had a much longer exposure period to salinity than the three early-season cultivars. However, moderate salinity does not seem to have a significant impact on growth and visual quality for ‘Dutch Master’, ‘Ice Follies’, or ‘Tete-a-Tete’ indicating that at least some saline water can be used for plant production without losses in plant quality.

Colored calla lilies (Zantedeschia K. Koch) are popular cut flowers and potted plants, which have a recommended irrigation water electrical conductivity (EC) of less than 1.5 dS m−1. Calla lilies exposed to an NaCl imposed EC up to four times the recommended EC showed no reductions in visual quality, with maintenance of growth, albeit at a reduced rate. The leaves of the plants in all treatments were able to maintain turgor even though there were decreases in carbon assimilation rate of 50–80% compared to the control in the 50 mM NaCl treatment starting 35 days after treatment. This reduction in photosynthesis is most likely responsible for the reductions we observed in growth. Within this same time period we observed osmotic adjustment of 0.16–0.20 MPa and reductions in stomatal conductance of 53–97% compared to the control. We propose that osmotic adjustment and reductions in stomatal conductance were integral in maintaining leaf turgor throughout the stress period. By 63 days of treatment the cation content (Na+, Ca2+ and Mg2+) in the leaves of the 25 and 50 mM NaCl treatments were two and three times the concentration observed in the control respectively. We hypothesize that osmotic adjustment is the result of ion accumulation. Osmotic adjustment in addition to reductions in stomatal conductance may be adaptations to ensure that colored calla lilies survive stressful conditions until their dormant period and reemerge successfully under more favorable conditions.

A good working knowledge of seed germination requirements is important for plant establishment for restoration and experimentation, particularly in wild plant species. Some seeds require a period of after-ripening and cold stratification before germination will occur. In this study we examined the effects of after-ripening and stratification time on seeds from three disjunct populations of Arabidopsis lyrata ssp. lyrata, from serpentine and limestone sand substrates of the Mid-Atlantic region of the United States. Differences among populations were evaluated through seed germination percentage and rate. Overall germination percentage and rate significantly varied by population, with seeds from the two serpentine populations having a lower germination percentage and rate than seeds from the limestone sand population. After-ripening time also significantly affected germination percentage and rate, with both measurements generally being the highest in 4 and 8 month-old seeds. Stratification did not ...

Salinity is a problem for crop production worldwide, which can affect not only the yield of ornamental plants, but also their quality. Calla lilies (Zantedeschia K. Koch) are a popular cut flower and landscape plant. In this study we examined how salinity applied either pre- or post-emergence altered shoot growth and flower production compared with standard growth conditions. Salinity applied post-emergence did not significantly affect shoot growth in either the 25- or 50-mm NaCl treatments; however, irrigation with a 50-mm NaCl solution did significantly reduce dry weight and flower production compared with the control. The most drastic effect on flower production was observed when the 50-mm treatment was applied pre-emergence. Although flowering time did not vary among treatments, in the spring, flowering success was less than 50% in the 50-mm treatment, which was significantly less than the other treatments. The plants in all treatments had good visual quality and high relative water content although the shoots of the salt-stressed plants had a Na+ content two to five times greater than the control. We hypothesize that the maintenance of visual quality may in part be the result of increased Ca2+ concentration (up to four times the amount in the control) in the shoots of the salt-stressed plants, which may have helped maintain turgor and cell membrane integrity under saline conditions. Our results indicate that use of irrigation water salinized by NaCl with an electrical conductivity (EC) more than twice as high as that recommended for optimal calla growth (1.5 dS·m−1 compared with 3.4 dS·m−1) can be used without a loss in plant quality, thereby increasing irrigation options for calla lilies, particularly in areas where high-quality water is scarce.

Guayule (Parthenium argentatum Gray) has been difficult to improve through classical plant breeding because of its facultative apomictic reproductive system and long growth period to harvest (2–5 years). Attempts have been made to increase rubber concentration and yield by selecting for traits correlated with rubber production. The objective of this study was to estimate heritability values in guayule that more accurately account for the contributions of apomictic and sexual reproduction occurring among populations, using a modified parent–progeny regression. Heritability was calculated using a modified version of the formula for single parent–progeny regression (h 2 = 2b): that is, h 2 = (2 – p)b, where p = proportion of apomixis and b = regression coefficient. Therefore, heritability was estimated as a range of values between the midparent and single parent regression, which correspond to complete apomixis and complete sexuality, respectively. At 2 years of growth, there was a significant regression between each parent trait and the corresponding progeny trait except rubber and guayulin B concentrations, with heritability estimates ranging from moderate to high for most parameters measured. Because apomixis occurs more frequently than sexual reproduction, most heritability estimates should fall closer to the midparent value, resulting in lower heritability. To increase resin and rubber yield in the progeny, selection should focus on plant height and width because these two traits are highly correlated with resin and rubber yield and have the highest heritability of the traits measured.

Guayule (Parthenium argentatum Gray) is being developed as a new commercial crop to be grown in arid and semiarid regions. Guayule stands are presently established using transplants; however, establishment by direct-seeding would reduce costs and make production more economical. A major difficulty in field establishment by direct-seeding is the variation in the quality of guayule seeds. Guayule seeds vary greatly in color, size, and weight, which are the attributes believed to be associated with the observed germination differences among and within seed lots. To determine the importance of these attributes, guayule seeds from different seed lots were separated by size (diameter) and color, each separation class was weighed and then seed quality determined by germination percentage and rate. X-ray analysis was used to distinguish filled from unfilled seeds, and this was related to the germination results. In six guayule breeding lines (N565, 11591, AZ-2, AZ-3, AZ-4, and AZ-5), the highest quality seeds were darker (opaque-black and gray), small to medium in diameter (1.4–1.6 mm), and were heavier (a greater proportion of filled seeds). Color appeared to be a more efficient separator for seed quality than seed size; however, separation by size may be acceptable on a large scale and still provide higher quality and more uniform seed lots.

Guayule (Parthenium argentatum Gray), a native of the Chihuahuan desert, produces the majority of its rubber during the winter months. Increased rubber production is thought to be induced by cold night temperatures, but the factors involved in rubber induction are not completely understood. The purpose of this study was to answer three questions about rubber production in the winter: (1) how do immature plants (

Guayule (Parthenium argentatum Gray), a latex producing shrub from northern Mexico and southwestern Texas, has been considered a viable alternative commercial crop for arid lands throughout the world. Stand establishment by direct seeding has been ineffectual because of problems with seed germination. Seed dormancy has been ascribed as one of the main reasons for low germination. Special seed treatments, such as physical and chemical conditioning, have been devised to overcome embryo and seed coat dormancy, thereby improving germination and emergence. However, the treatments described in the literature have not been as effective as expected, and many of them are costly and time consuming. The objective of this study was to determine the effects of nine preconditioning treatments on the percentage and rate of germination and emergence, and seedling fresh weight. Three-year-old seed of lines AZ-101, AZ-3, and N9-3 were analyzed with X-ray to determine the seed lot quality. The results showed differences in quality (defined as seeds containing embryos and endosperm) among the three lines; however, no differences were found for percentage and rate of germination and emergence, and seedling fresh weight among the nine treatments. These results suggest that in older seed lots seed quality is of greater importance in determining germination and emergence than conditioning treatments.

Guayule (Parthenium argentatum A. Gray) is naturally subject to periods of water stress in its native habitat. It has been shown that, under cultivation, rubber yields increase with increasing irrigation, but rubber concentration per plant decreases. The effect of irrigation on resin concentration is unclear. The purpose of this study was to understand how resin concentration is affected by water stress, and why water stress increases rubber concentration. Greenhouse-grown guayule plants were subjected to water stress in four experiments, each of 3 mo duration. Two experiments were conducted in the summer, the active growth period, and two experiments were conducted in the winter. The water-stressed plants were irrigated when the average soil water potential reached either -0.6 MPa (first summer experiment) or -0.3 MPa (all subsequent experiments). Water-stress effects were monitored by measuring growth, C exchange, biomass, and resin and rubber production. Water-stressed plants had lower C exchange, growth, and leaf-to-stem ratio than well-watered plants. Resin concentration did not respond consistently to water stress. Rubber concentration was generally higher in the water-stressed plants than in the well-watered plants as a result of decreased leaf biomass in both the summer (33 vs. 45 g kg -1 ) and winter (36 vs. 52 g kg -1 ) and decreased stem diameter in the summer (8.1 vs. 11.0 mm). Rubber is deposited mainly in the bark; therefore, reduced leaf biomass and stem diameter contribute to higher rubber concentration in the water-stressed plants by increasing the relative amount of bark.

Species with widespread distributions that grow in varied habitats may consist of ecotypes adapted to a particular habitat, or may exhibit cross-tolerance that enables them to exploit a variety of habitats. Populations of Arabidopsis lyrata ssp. lyrata (L.) O’Kane & Al-Shehbaz grow in a wide variety of edaphic settings including serpentine soil, limestone sand, and alluvial flood plains. While all three of these environments share some stressors, a crucial difference among these environments is soil calcium to magnesium ratio, which ranges from 25∶1 in the limestone sand to 0.2∶1 in serpentine soil. The three populations found on these substrates were subjected to three different Ca to Mg ratios under controlled environmental conditions during germination and rosette growth. Response to Ca to Mg ratio was evaluated through germination success and radicle growth rate, rosette growth rate, and the content of Ca and Mg in the rosette. All three populations were particularly efficient in fueling growth under nutrient deficiency, with the highest nutrient efficiency ratio for Ca under Ca deficiency and for Mg under Mg deficiency. Although the serpentine population had significantly higher leaf Ca to Mg ratio than the limestone or flood plain populations under all three Ca to Mg ratios, this increase did not result in any advantage in growth or appearance of the serpentine plants, during early life stages before the onset of flowering, even in the high Mg substrate. The three populations showed no population by substrate interaction for any of the parameters measured indicating that these populations may have cross-tolerance to substrate Ca to Mg ratio.

Guayule (Parthenium argentatum Gray) has been difficult to improve through classical plant breeding because of its facultative apomictic reproductive system. Attempts have been made to increase rubber concentration and yield by examining traits correlated with rubber production and their heritabilities. We propose a new way of estimating heritability in guayule that more accurately accounts for the contributions of apomictic and sexual reproduction. At two years of growth, there was a significant relationship between the parents and the progeny for all traits measured, except for rubber and guayulin B concentrations. Due to the facultative apomictic nature of guayule reproduction, heritabilities are more accurately presented as a range of values between the narrow and broad sense heritabilities. Since guayule is more apomictic than sexual, most heritabilities will be closer to the broad sense values. To increase resin and rubber yield in the progeny, selection should focus on height and width in the parents because height and width are highly correlated with rubber yield, with the highest heritabilities (0.65 to 1.00 and 0.97 to 1.0, respectively) of the traits measured.

As a native of the Chihuahuan desert, guayule (Partheniumargentatum Gray) has a history of dealing with low water availability. Agronomic studies have shown that increasing irrigation increases overall rubber yields, but decreases rubber concentration per plant. As water availability is an important factor in agricultural production, this study was conducted to examine how drought affects plant growth and secondary compound distribution throughout the plant. One-year-old guayule plants were subjected to water stress from June through August, in 2003 and 2004. The well-watered treatment was irrigated daily, and the drought-stressed plants were irrigated when the soil water potential reached 6 (0.6) or 3 (0.3) bars (megapascals) in 2003 and 2004, respectively. Plant growth was monitored by measuring height, width, and stem diameter. Fresh weight of shoots and roots was recorded at harvest, and a subset of plants were defoliated and used to determine leaf weight and area. Resin and rubber were extracted from dried and ground plant samples. Growth, leaf weight, and leaf to stem ratio were decreased in the drought-stressed plants compared to the well-watered plants. Rubber concentration, but not resin concentration, was higher in the drought-stressed plants. There were no significant differences in resin and rubber concentration in the leaves and roots of the different treatments; however, they were both higher in the stems of the drought-stressed plants. In guayule, rubber is deposited mainly in the bark parenchyma of the stems. The drought-stressed plants had a greater contribution of stem biomass to overall biomass and a reduced stem diameter with higher bark to wood ratio, which could account for the higher rubber concentration in the drought-stressed plants.