Search Results

You are looking at 1 - 10 of 17 items for :

  • Author or Editor: Mengmeng Gu x
  • HortScience x
Clear All Modify Search

Texas mountain laurel (Sophora secundiflora) is a native shrub tolerating drought, heat, windy conditions, and alkaline or wet soils. However, its availability is somewhat low and little information is available on nutrient requirement and other culture information. Two greenhouse experiments were conducted to quantify the responses of Texas mountain laurel to different forms and rates of nitrogen (N) fertilizer. In Expt. 1, 1-year old seedlings were treated for 194 days with three NO3:NH4 ratios at 25:75, 50:50, and 75:25 and two rates of N at 100 and 200 mg·L−1 in a factorial design. There was no interaction between the N rate and form on any growth parameters. Nitrogen form did not significantly affect shoot dry weight, root dry weight, root–to-shoot ratio, or the total dry weight. There was no significant difference between N rate of 100 and 200 mg·L−1 on root dry weight, root-to-shoot ratio, or the total dry weight. The shoot dry weight of Texas mountain laurel fertilized with 100 mg·L−1 was higher compared with that of the plants fertilized at 200 mg·L−1. The reduced shoot dry weight at N of 200 mg·L−1 was the result of the higher substrate salinity. In Expt. 2, seedlings were fertilized with five N rates (50, 100, 150, 200, and 250 mg·L−1) for 203 days. Plants watered with 150, 200, and 250 mg·L−1 were taller than those fertilized with 50 mg·L−1. The shoot height of plants watered with 100 mg·L−1 was only significantly different from 50 mg·L−1. For rapid growth of Texas mountain laurel, a N rate range of ≈150 mg·L−1 was recommended supplied with a combination of NO3-N and NH4-N in the ratios of 0.3 to 3.0.

Free access

Green light penetrates deeper into the plant canopy because of its high transmittance and reflectance, and may potentially increase light interception and whole-canopy photosynthesis, whereas red and blue light is absorbed primarily by upper leaves. Moreover, green light induces shade avoidance responses and regulates secondary metabolism in plants. In this study, we investigated the effects of substituting partial red and/or blue light with green light on plant growth and development in basil (Ocimum basilicum) ‘Improved Genovese Compact’ (green) and ‘Red Rubin’ (purple) plants. There were four treatments: one combined red and blue (R&B) light treatment, R76B24 [the proportion of red (R) and blue (B) light was 76% and 24%, respectively]; and three green (G) light treatments—R44B24G32, R74B16G10, and R42B13G45—with green light proportions of 32%, 10%, and 45%, respectively. The experiment was conducted in a growth room and the photosynthetic photon flux density (PPFD) of all treatments was set at 220 μmol·m−2·s−1 with a 16-h photoperiod. Plants were subirrigated as needed using a nutrient solution with an electrical conductivity (EC) of 2.0 dS·m−1 and a pH of 6.0. The net photosynthetic rate (Pn) in lower leaves was unaffected by green light treatments in green basil plants, whereas in purple basil plants it increased by 59% and 45% under treatments R44B24G32 and R74B16G10, respectively, compared with the combined R&B light. In green basil plants, treatments R44B24G32 and R42B13G45 induced stem elongation, but green light treatments showed no effects on petiole elongation, leaf expansion, leaf thickness, or plant yield. In purple basil plants, treatments R44B24G32 and R42B13G45 induced stem elongation and decreased leaf thickness and plant yield, but only the R42B13G45 treatment induced petiole elongation, and green light treatments showed no effects on leaf expansion. Concentrations of anthocyanin, phenolics, and flavonoids, and antioxidant capacity in green basil leaves showed no differences between treatments R76B24 and R44B24G32, but decreased under treatments R74B16G10 and R42B13G45. Concentrations of phenolics and flavonoids, and antioxidant capacity in purple basil leaves showed no differences between treatments R76B24 and R74B16G10, but decreased under treatments R44B24G32 and R42B13G45. Combining plant yield, nutritional values, and the working environment for growers, a white light with low green light proportion (≈10%) is recommended for basil production in a controlled environment.

Free access

Use of reclaimed water to irrigate urban landscapes will likely increase because fresh water supply is diminishing and the population continues to grow in the semiarid southwestern United States. Salt tolerance of two native landscape woody ornamentals, Texas mountain laurel (Sophora secundiflora) and Mexican redbud (Cercis canadensis var. mexicana), was investigated in a greenhouse experiment. Seedlings of the two species were grown in two substrates mixed with composted mulch and a commercial potting mix at two ratios and irrigated with saline solutions at three salinity levels: 1.6 (control, nutrient solution), 3.0, or 6.0 dS·m−1 electrical conductivity (EC). There was no interaction between substrate and EC of irrigation water. Foliar salt damages such as leaf drop, leaf curl, and edge burn were observed in Mexican redbud when the plants were irrigated with solutions at EC of 3.0 and 6.0 dS·m−1. No symptoms were observed on Texas mountain laurel plants, although plants irrigated at EC of 3.0 and 6.0 dS·m−1 were smaller compared with controls. Shoot growth and elongation of both species were reduced by the elevated salinity of irrigation water, and the reduction in Mexican redbud was greater than Texas mountain laurel. Leaf photosynthesis rate and leaf stomatal conductance were also reduced in Texas mountain laurel by the elevated salinity of irrigation water. Tissue Na+ and Cl concentrations were higher in Texas mountain laurel irrigated with water of elevated salinity.

Free access

Crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae Kuwana), a fast-spreading invasive insect, has been causing damage to popular landscape plants in at least 17 states in the United States since 2004. This invasive insect has a list of documented plant hosts in ∼23 genera, which includes its primary hosts, crapemyrtles (Lagerstroemia spp.), as well as other important plant species, such as pomegranates, apple, and the native plant American beautyberry. Previous studies have shown CMBS causes different levels of feeding damage among its plant hosts, while the underlining plant defense mechanisms toward CMBS attacks remain elusive. A better understanding of plant–CMBS interactions and how CMBS performs under different plants (e.g., a susceptible vs. a resistant host) can provide valuable guidance for integrated pest management. Therefore, in this study, we conducted the age-stage, two-sex table study analysis to evaluate the biological parameters of CMBS on different species or cultivars of crapemyrtle under laboratory conditions (25 °C and 250 μmol·m−2·s−1 light with a photoperiod of 12 hours:12 hours (light:dark). Crapemyrtle bark scale development was found to be greatly influenced by the hosts. This study aims to provide important biological and ecological data on CMBS using a comprehensive life table study to gain a thorough understanding of its development, survival, and fecundity on different crapemyrtle species or cultivars.

Open Access

Seasonal variations of nutrient concentrations in soil and apple leaves, soil properties, weed density, and tree performance were observed for response to four groundcover managements systems: 1) mowed control; 2) plastic woven landscape fabric; 3) wood chip mulch; and 4) shredded commercial paper mulch. Soil sampled below the wood chip and shredded paper mulch treatments had higher NO3-N concentrations during the season. Soil below the shredded paper mulch had greater soil Ca, Na, and Zn than other treatments. Soil sampled below wood chip mulch had higher Mg and B. Leaf K was greater for trees grown with bark chip mulch than the other treatments. Overall, the seasonal patterns of N, P, and K decreased and had similar patterns as previously reported conventionally grown orchards. The leaf Ca and Mg increased during the season for all treatments. The concentration of other microelements had patterns similar among all treatments. Seasonal soil pH decreased during the season and was affected by treatments. During the season, water infiltration was faster into the soil covered with shredded paper mulch. The organic matter was greater in soil under the wood chip mulch at the 15-cm soil depth. Very little weed invasion occurred in the landscape fabric through August. Trees grown with shredded paper and wood chip mulch treatments had greater trunk cross-sectional area compared to trees grown under landscape fabric after 5 years; however, the latter treatment resulted in greater tree height, tree canopy spread, and fruit yield.

Free access

It has been observed that paper birch (Betula papyrifera Marsh.) has significant leaf abscission under mild to severe water stress. One-year-old paper birch seedlings were exposed to water deficit, ethylene, or inhibitors of ethylene action under controlled conditions to study water-stress induced leaf abscission. Exposing well-watered and water-stressed paper birch to 20 ppm of ethylene for 96 hours resulted in more than 50% leaf abscission regardless of plant water status, while water stress alone did not cause leaf abscission. However, the application of 1 ppm ethylene did not cause leaf abscission. Exposure to 1 ppm 1-methylcyclopropene or treatment with 0.1 mM of silver thiosulfate did not affect predawn water potential, gas exchange, and chlorophyll fluorescence. The measured evolved ethylene did not significantly increase in water-stressed paper birch prior to leaf abscission. Based on these observations, ethylene would appear to play a minor role in water-stress induced leaf abscission in paper birch.

Free access

Japanese beetle (Popilla japonica Newman) has caused severe damage on a wide range of horticultural crops since its first introduction to the Eastern United States from Japan in 1916. Leaves are skeletonized by adult beetles feeding in masses, which makes this insect damage easy to identify. In Arkansas, Japanese beetle was first trapped in Washington County in 1997 and has reached epidemic proportions in the most recent three years. Leaf skelotonization and feeding preference on eighteen birch accessions by Japanese beetle were recorded in 2003 and 2004. There was a wide range from no feeding (0% leaf skelotonization) to high feeding preference (89% leaf skelotonization). Betula utilis var. jacquemontii and B. papyrifera `Renaissance Upright' had highest preference. Betula pendula `Laciniata' had no feeding damage from Japanese beetle.

Free access

Four birch taxa, Betulaalleghaniensis, B. davurica, B. nigra `Heritage', and B. papyrifera, were grown in a greenhouse and exposed to water deficit stress for 35 days. Daily water was withheld from the plants until the combined weight of each container and the plant was reduced to 40% of the control. Supplemental water was supplied to each container to maintain 40% of the initial combined weight. Predawn water potential, gas exchange, and abscised leaf area were measured daily during the first week and at 3-day intervals after the first week. Predawn water potential dropped to lowest value before the containers were rehydrated and remained low throughout the treatment period. Net CO2 assimilation (A), stomatal conductance (gs) and evapotranspiration (Et) of all taxa decreased significantly during the first week of water deficits. Changes in A and Et varied among taxa after the first week of water deficits. Water use efficiency (WUE = A/Et) of four birch taxa decreased to significant lower values than control in the first week that water was withheld, and then increased to significantly higher values than control. Gas exchange data were fit into 2- or 3-segmented linear model. The type and shape of the models, and the joint of each segment gave an indication of how the gas exchange responded to the long-term water deficit stress. At the end of the water deficit treatment, B. papyrifera had abscised most of its leaves and maintained a high A, while B. alleghaniensis maintained more leaves on the tree, but had a relatively low A.

Free access

Mustard Seed Meals (MSMs) are by-products of biodiesel and an alternative to conventional herbicides for organic farming. However, MSMs might also suppress the emergence of vegetable seedlings. The objective of this study was to determine the response of vegetable seedling emergence to different MSM types and rates applied as an alternative herbicide. Six types of vegetable seeds, onion (Allium cepa), two cultivars of lettuce (Lactuca sativa ‘Black Seeded Simpson’ and ‘Buttercrunch’), mustard (Brassica juncea), kale (Brassica oleracea), and Mizuna (Brassica rapa var. japonica), were sowed in petri dishes containing germination mix. MSMs (Sinapis alba ‘IdaGold’ and B. juncea ‘Pacific Gold’) were incorporated into the germination mix at 0, 88, 176, or 265 g·m−2. Petri dishes were sealed for 1, 3, 5, or 7 days after sowing. For onion, ‘Pacific Gold’ had a greater suppressive effect on seedling emergence than ‘IdaGold’. For kale and mustard, ‘IdaGold’ and ‘Pacific Gold’ had similar suppressive effects on seedling emergence, but ‘Pacific Gold’ delayed emergence of kale at 88 g·m−2 when sealed for 3, 5, and 7 days. For Mizuna, ‘IdaGold’ had more suppressive effects than ‘Pacific Gold’ on seedling emergence, while sealing delayed but did not decrease emergence percentage (EP) at the lower rate (88 g·m−2) compared with the control treatment. For ‘Buttercrunch’ lettuce, there were no differences in the suppressive effects between the two MSMs. For ‘Black Seeded Simpson’ lettuce, ‘Pacific Gold’ had more suppressive effects on seedling emergence than ‘IdaGold’ when sealed at the lower rate (88 g·m−2) for longer durations (7 days) or at higher rates (176 and 265 g·m−2) for shorter durations (1 and 3 days). These results suggest that MSMs might suppress vegetable seedling emergence when applied at high rates (176 and 265 g·m−2), and sealing for more than 7 days after sowing may strengthen the suppressive effect. Extending sealing duration at the medium rates could achieve similar weed control results to high rates without sealing.

Free access