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Michelle M. Wisdom, Michael D. Richardson, Douglas E. Karcher, Donald C. Steinkraus and Garry V. McDonald

Early-spring flowering bulbs can increase biodiversity while adding color to lawns and other grassy areas. However, few studies have investigated whether bulbs can flower and persist in warm-season lawns or provide feeding habitat for pollinating insects. Thirty early-spring flowering bulbs, including species of Anemone, Chionodoxa, Crocus, Eranthis, Hyacinthus, Ipheion, Iris, Leucojum, Muscari, and Narcissus, were established in bermudagrass (Cynodon dactylon L. Pers) and buffalograss [Buchloe dactyloides (Nutt.) J.T. Columbus] lawns in late autumn 2015 in Fayetteville AR. Bulbs were assessed over three growing seasons for flowering characteristics, persistence, and their ability to attract pollinating insects. A growing degree day model was also developed to predict peak flowering times in our region. Numerous bulb entries produced abundant flowers in bermudagrass and buffalograss lawns in the first year after planting, but persistence and flower production were reduced in both the second and third years of the trial. Five bulbs persisted for multiple years in both turfgrass species and continued to produce flowers, including Crocus flavus Weston ‘Golden Yellow’ (crocus), Leucojum aestivum L. (spring snowflake), Narcissus (daffodil) ‘Baby Moon’, Narcissus ‘Rip Van Winkle’, and Narcissus ‘Tete-a-Tete’. Several bulbs, primarily crocuses and Muscari spp. (grape hyacinth), were also observed to attract pollinating insects, principally honey bees (Apis mellifera). These results demonstrate that some early-spring bulbs can persist in competitive warm-season turfgrasses, while providing pollinator forage, but species and cultivar selection is critical for long-term success.

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Yuxiang Wang, Youping Sun, Genhua Niu, Chaoyi Deng, Yi Wang and Jorge Gardea-Torresdey

Ornamental grasses are commonly used in urban landscapes in Utah and the Intermountain West of the United States. The relative salt tolerance of Eragrostis spectabilis (Pursh) Steud. (purple love grass), Miscanthus sinensis Andersson ‘Gracillimus’ (maiden grass), Panicum virgatum L. ‘Northwind’ (switchgrass), and Schizachyrium scoparium (Michx.) Nash (little bluestem) were evaluated in a greenhouse. Plants were irrigated with a nutrient solution at an electrical conductivity (EC) of 1.2 dS·m–1 (control), or saline solution at an EC of 5.0 or 10.0 dS·m–1. At harvest (65 days after the initiation of treatment), P. virgatum and S. scoparium exhibited no foliar salt damage, and E. spectabilis and M. sinensis had minimal foliar salt damage when irrigated with saline solution at an EC of 5.0 dS·m–1. At an EC of 10.0 dS·m–1, P. virgatum and S. scoparium still had no foliar salt damage, but E. spectabilis and M. sinensis displayed slight foliar salt damage, with visual scores greater than 3 (0 = dead; 5 = excellent). Compared with the control, saline solution at an EC of 5.0 and 10.0 dS·m–1 reduced the shoot dry weight of all ornamental grasses by 25% and 46%, respectively. The leaf sodium (Na+) concentration of E. spectabilis, M. sinensis, P. virgatum, and S. scoparium irrigated with saline solution at an EC of 10.0 dS·m–1 increased 14.3, 52.6, 5.3, and 1.7 times, respectively, and the chloride (Cl) concentration increased by 9.4, 11.1, 2.8, and 2.7 times, respectively. As a result of the salt-induced water deficit, plant height, leaf area, number of inflorescences and tillers, net photosynthesis rate (Pn), stomatal conductance (g S), and transpiration rate of four tested ornamental grasses decreased to some extent. Although high Na+ and Cl accumulated in the leaf tissue, all ornamental grass species still had a good visual quality, with average visual scores greater than 3. In conclusion, all ornamental grasses showed a very strong tolerance to the salinity levels used in this research.

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Zhengnan Yan, Dongxian He, Genhua Niu, Qing Zhou and Yinghua Qu

Few researchers examined different red light amounts added in white light-emitting diodes (LEDs) with varied daily light integrals (DLIs) for hydroponic lettuce (Lactuca sativa L.). In this study, effects of DLI and LED light quality (LQ) on growth, nutritional quality, and energy use efficiency of hydroponic lettuce were investigated in a plant factory with artificial lighting (PFAL). Hydroponic lettuce plants (cv. Ziwei) were grown for 20 days under 20 combinations of five levels of DLIs at 5.04, 7.56, 10.08, 12.60, and 15.12 mol·m−2·d−1 and four LQs: two kinds of white LEDs with red to blue ratio (R:B ratio) of 0.9 and 1.8, and two white LEDs plus red chips with R:B ratio of 2.7 and 3.6, respectively. Results showed that leaf and root weights and power consumption based on fresh and dry weights increased linearly with increasing DLI, and light and electrical energy use efficiency (LUE and EUE) decreased linearly as DLI increased. However, no statistically significant differences were found in leaf fresh and dry weights and nitrate and vitamin C contents between DLI at 12.60 and 15.12 mol·m−2·d−1. Also, no effects of LQ on leaf dry weight of hydroponic lettuce were observed at a DLI of 5.04 mol·m−2·d−1. White plus red LEDs with an R:B ratio of 2.7 resulted in higher leaf fresh weight than the two white LEDs. LUE increased by more than 20% when red light fraction increased from 24.2% to 48.6%. In summary, white plus red LEDs with an R:B ratio of 2.7 at DLI at 12.60 mol·m−2·d−1 were recommended for commercial hydroponic lettuce (cv. Ziwei) production in PFALs.

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Neo Edwin Nyakane, Moosa Mahmood Sedibe and Elisha Markus

The objective of this study was to evaluate the effects of the Ca:Mg ratio, magnetic field (MF), and mycorrhizal amendment on the yield and mineral composition of rose geranium. The experiment was structured as a 3 × 2 factorial experimental design, with three levels of the Ca:Mg ratio (2.40:6.78, 4.31:4.39, and 6.78:2.40 meq·L−1), 6.78 Ca:2.40 Mg meq·L−1 denoted by “High-Ca:Low-Mg,” equal proportion of Ca and Mg (4.31 Ca:4.39 Mg meq·L−1) represented by “EP-Ca:Mg,” and 2.32 Ca:6.38 Mg meq·L−1 denoted by “Low-Ca:High-Mg,” two levels of MF (no MF, denoted by “0 MF,” and 110 mT, denoted by “1 MF”) and split treatments of mycorrhizae (zero mycorrhizae denoted by “0 Myco,” and 20 mL mycorrhizae denoted by “1 Myco”) were used in this study. The results show that the plant height and branch dry mass were significantly (P < 0.05) affected by the Ca:Mg ratio. No significant effect of Ca:Mg ratio, MF, or mycorrhizae on the number of leaves, foliar mass, leaf dry mass, or yield was detected. Phosphorus, K, S, Fe, and B accumulation in the stem were unaffected, as were leaf N, P, K, Ca, S, Fe, B, and Cu. However, some agronomic attributes (plant height, number of branches, root length, and chlorophyll content) and mineral composition (Stem-N) were optimized when the 1 MF exposed nutrient solution was used with about equal proportions of Ca and Mg. This Ca:Mg ratio in the nutrient solution, together with the exposure of rose geranium plants to 1 MF, yielded positive results. The findings of this study can be applied to improve the production of rose geranium by enhancing the growth and mineral concentration of this crop.

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Bernadine C. Strik and Amanda J. Vance

The relationship between individual berry weight and viable seed number of small- (<15 mm), medium- (15–19 mm), and large-diameter (>19 mm) berries was studied over 2 years in nine cultivars (Aurora, Bluecrop, Bluegold, Draper, Duke, Liberty, Legacy, Ozarkblue, and Reka) through their harvest seasons. Plants were grown with two different preplant amendment-mulch treatments, but this treatment had no effect on the variables measured, so data were pooled. The highest average seeds/berry was in ‘Bluecrop’ (55.5) and ‘Duke’ (50.0) and the lowest in ‘Bluegold’ (17.1), ‘Aurora’ (22.5), and ‘Liberty’ (23.5). Average berry weight over the fruiting season ranged from 1.79 and 1.80 g for ‘Liberty’ and ‘Reka’, respectively, to 2.30 and 2.44 g in ‘Ozarkblue’ and ‘Draper’, respectively. The average number of seeds/berry was higher in 2010 than in 2009 for all cultivars, ranging from 14% higher in ‘Reka’ to 96% higher in ‘Liberty’. The flowering period was earlier in 2010 than in 2009, but bloom was concentrated in 2009 (28 days) compared with 2010 (45 days), likely affecting pollinator success. In general, seeds/berry and berry weight declined through the harvest season. Some cultivars had a considerable difference in the number of seeds in large-sized than in small-sized berries (e.g., 89%, 107%, 108%, and 147% more seeds in ‘Aurora’, ‘Reka’, ‘Bluegold’, and ‘Liberty’, respectively), whereas others had relatively little difference (14% and 36% in ‘Draper’ and ‘Bluecrop’, respectively). There was a linear relationship between berry weight and viable seeds/berry. Cultivars did not differ in the berry weight per seed (slope of the line) between the 2 years, except for ‘Draper’ (only significant in 2009), ‘Legacy’, and ‘Reka’. ‘Bluegold’ had the greatest berry weight per seed and ‘Reka’ the lowest. The weakest relationship between berry weight and seed number was in ‘Draper’. Cultivars that produced parthenocarpic fruit of marketable size were ‘Aurora’, ‘Bluegold’, and ‘Liberty’. ‘Duke’, ‘Legacy’, ‘Reka’, and ‘Ozarkblue’ produced commercially acceptable fruit (0.75–1.0 g) with fewer than 7 seeds/berry. By contrast, some cultivars required a relatively large number of seeds to produce a berry including ‘Bluecrop’ (28–40 seeds), ‘Draper’ (15–23 seeds), and ‘Legacy’ in 2010 (20 seeds). The number of seeds per berry accounted for as much as 87% of the variability in berry weight indicating the importance of good pollination and seed set for berry weight and yield in these cultivars.

Open access

Garry V. McDonald and Wayne A. Mackay

The University of Arkansas Horticulture Department was charged in 2016 by university administration to develop and implement a student learning outcome (SLO)-based assessment plan. The Horticulture Department curriculum committee was tasked to develop such a plan. Various models were considered, but ultimately a modified plan based on the work of M.P. Pritts and T. Park was adopted. Adjustments were based on student population size and particular requirements that had to be integrated with the university-mandated SLO goals and objectives. Two phases of a student’s academic career were chosen to access: an incoming freshman or transfer phase and a late-term or degree completion phase. Specific learning outcomes and goals were identified as well as courses and activities that would reasonably be measured while meeting university requirements. Data collection on entering freshmen and transfer students started in Fall 2018. The full impact of the implemented plan will not be known until 2020, when the first full cohort of incoming freshmen reaches the terminal stage of the degree program.

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Brian M. Irish, Ricardo Goenaga, Sirena Montalvo, Bernardo Chaves-Cordoba and Inge Van den Bergh

Bananas are one of the most important fruits, serving as a cash crop and staple food in many regions of the world. In Puerto Rico, bananas are an important agricultural industry, supplying all the fruit needed for local demand. Diseases significantly limit production, and the evaluation and adoption of improved genetic resistance in bananas might provide an avenue for long-term sustainable production. To this end, nine enhanced genotypes from international selection and breeding programs were introduced and evaluated for their response to black leaf streak (BLS) (Pseudocercospora fijiensis Morelet) and for their agronomic performance. Bananas were evaluated as part of a collaborative effort between the U.S. Department of Agriculture Agricultural Research Service (USDA-ARS) Tropical Agriculture Research Station (TARS) and Bioversity International’s International Musa Testing Program (IMTP). Improved genotypes were compared with disease-resistant and disease-susceptible reference genotypes across two cropping cycles. Field plants were grown following commercial production practices with no BLS management. Significant differences in disease reactions were observed during both cropping cycles for test and reference genotypes. Under high disease pressure, ‘FHIA-21’, ‘FHLORBAN 916’, and ‘FHLORBAN 920’ test genotypes showed higher numbers of functional leaves and lower disease severity at harvest in both cycles. Short cycling times were also observed for the two FHLORBAN genotypes. Larger bunches with a high number of fruits were produced by the ‘IBP 12’, ‘IBP 5-B’, and ‘IBP 5-61’ selections. Several of the GCTCV test genotypes were extremely susceptible to BLS, did not perform as expected, and appeared to be off-types. Several of the test genotypes performed well, although currently none possessed all needed traits for a commercial banana substitute. Regardless, several test genotypes have agronomic potential because they have been selected for disease resistance to other important pathogens (e.g., fusarium wilt) and therefore have become part of the permanent TARS collection. Future efforts will continue to focus on the IMTP collaboration and introduction of promising banana genotypes for evaluations.

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Kang-Di Hu, Xiao-Yue Zhang, Sha-Sha Wang, Jun Tang, Feng Yang, Zhong-Qin Huang, Jing-Yu Deng, Si-Yuan Liu, Shang-Jun Zhao, Lan-Ying Hu, Gai-Fang Yao and Hua Zhang

Hydrogen sulfide (H2S) has been proven to be a multifunctional signaling molecule in plants. In this study, we attempted to explore the effects of H2S on the climacteric fruit tomato during postharvest storage. H2S fumigation for 1 d was found to delay the peel color transition from green to red and decreased fruit firmness induced by ethylene. Further investigation showed that H2S fumigation downregulated the activities and gene expressions of cell wall–degrading enzymes pectin lyase (PL), polygalacturonase (PG), and cellulase. Furthermore, H2S fumigation downregulated the expression of ethylene biosynthesis genes SlACS2 and SlACS3. Ethylene treatment for 1 d was found to induce the expression of SlACO1, SlACO3, and SlACO4 genes, whereas the increase was significantly inhibited by H2S combined with ethylene. Furthermore, H2S decreased the transcript accumulation of ethylene receptor genes SlETR5 and SlETR6 and ethylene transcription factors SlCRF2 and SlERF2. The correlation analysis suggested that the fruit firmness was negatively correlated with ethylene biosynthesis and signaling pathway. The current study showed that exogenous H2S could inhibit the synthesis of endogenous ethylene and regulate ethylene signal transduction, thereby delaying fruit softening and the ripening process of tomato fruit during postharvest storage.

Open access

Andrew K. Miles, Malcolm W. Smith, Nga T. Tran, Timothy A. Shuey, Megan M. Dewdney and André Drenth

Citrus black spot is an important fungal disease of citrus resulting in fruit drop and rind blemish in tropical and subtropical production areas. The disease is incited by the fungus Phyllosticta citricarpa (McAlpine) van der Aa (synonym: Guignardia citricarpa Kiely), with control currently relying on the application of fungicides. Because the presence and expression of resistance is poorly understood, we sought to develop a method for inoculating fruit in the field that gives reproducible symptoms of citrus black spot consistent with natural field infection. We subsequently validated this method by screening 49 citrus accessions and characterized their qualitative expression of citrus black spot symptoms. Challenge inoculations were undertaken with a known isolate of P. citricarpa, and control fruit were inoculated with water or the endophyte P. paracapitalensis Guarnaccia & Crous. Our results showed that all mandarin, sweet orange, lemon and papeda types were susceptible; pummelo, lime, and sour orange types expressed immunity; while various hybrids were susceptible, resistant and immune. Hybrid progeny from crosses using pummelo [Citrus maxima (Burm.) Merr.] as a parent showed preliminary evidence of segregation for citrus black spot immunity. The implications of these results to achieve genetic improvement for citrus black spot resistance in citrus breeding programs are discussed.

Open access

Suzanne P. Stone, George E. Boyhan and W. Carroll Johnson III

The southeastern United States produces 50% of U.S. conventional watermelon (Citrullus lanatus) but only 7% of U.S. organic watermelon. Weeds are a major threat to watermelon yield in the southeastern United States, and organic weed control is estimated to cost 20-times more than conventional herbicide programs. The objectives of this study were to determine the optimal weed control regime to reduce hand-weeding costs while maintaining yield and to compare the weed suppression of two watermelon types with differing growth habits in an organic system. In 2014 and 2015, watermelon plots were randomly assigned to the following treatments in a factorial arrangement: vine or compact growth habit; 1.0- or 0.5-m in-row spacing; and weekly weed control (kept weed-free by hoeing and hand-pulling weeds) for 0, 4, or 8 weeks after transplanting (WAT). At the time of the watermelon harvest, not weeding resulted in average total weed densities of 86.6 and 87.0 weeds/m2, and weeding for 4 WAT resulted in average total weed densities of 26.4 and 7.0 weeds/m2 in 2014 and 2015, respectively. Nonetheless, weeding for 4 WAT resulted in watermelon yields and fruit counts comparable to those of weeding for 8 WAT during both years. This partial-season weeding regime resulted in 67% and 63% weeding cost reductions for vine and compact plants, respectively, in 2014, and a 43% reduction for both growth habit types in 2015. In 2015, a separate experiment that evaluated weeding regimes that lasted 0, 1, 2, 3, 4, and 8 WAT found that yields resulting from weeding for 3 WAT were greater than those resulting from weeding for 2 WAT. However, the yields did not differ when weeding was performed for 4 WAT and 8 WAT.