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  • Author or Editor: M. F. George x
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Abstract

Sleeved poinsettia plants (Euphorbia pulcherrima, Willd. cvs. Annette Hegg Supreme and Annette Hegg Dark Red) stored best at 10°C. Lower temperatures (2-7°C) induced chilling damages as manifested mainly by bract blueing. Higher temperatures (up to 16°) resulted in increased leaf petiole epinasty and bract drooping. The bract blueing and leaf petiole epinasty disorders became worse as storage duration increased from 2 to 10 days, while bract drooping decreased during this same period. Plants sleeved and stored in paper were generally of higher quality upon removal than those sleeved and stored in plastic. Under relatively static conditions (15m/minute air speed), poinsettias froze at about −4°. Sleeving poinsettias delayed low-temperature damage. The injury of sleeved poinsettias was related to temperature, air speed, and exposure time which can be estimated by: time to injury (minutes) = 3.94 × chill factor (°C) + 61.9.

Open Access

A growth analysis was made of UV-B sensitive (`Poinsett') and insensitive (`Ashley') cultivars of Cucumis sativus L. grown in growth chambers at 600 μmol m-2 s-1 of photosynthetically active radiation (PAR) provided by red- and far-red-deficient metal halide (MH) or blue- and UV-A- deficient high pressure sodium/deluxe (HPS/DX) lamps. Plants were irradiated 6 h daily with 0.2 (-UV-B) or 18.2 (+UV-B) kJ m-2 d-1 of biologically effective UV-B for 15 days from time of seeding. In general, plants given +UV-B vs. -UV-B treatment showed lower specific leaf area (SLA) and leaf area ratio (LAR), higher specific leaf mass (SLM), mean relative growth rate (MRGR), and net assimilation rate (NAR), and no difference in leaf mass ratio (LMR). Plants grown under HPS/DX lamps vs. MH lamps had higher SLM and NAR, lower SLA, LAR, and LMR, and no difference in MRGR. Cultivar affected only LMR. PAR source and/or cultivar did not affect plant response to UV-B radiation.

Free access

Abstract

Stems of 49 woody species native to North America were collected from the field in Minnesota in January and subjected to controlled freezing tests. Characterization of the freezing process of xylem tissues by differential thermal analysis revealed that some species had no exotherms at low temperatures, some had small exotherms between –41° and –47°C, and others had large exotherms in the same temperature range. Generally very hardy species with ranges extending into northern Canada and Alaska had no exotherms. Species with small exotherms were native to the northern United States and southern Canada, and large exotherms were generally characteristic of the least hardy species studied. The low temperature exotherms occurred at the same temperature that results in xylem death of most of the plants studied. Plants with low temperature exotherms tend to have ring-porous xylem and the temperature of the low temperature exotherms was correlated with the minimum temperatures of the boundaries of the northern range of the species tested.

Open Access

Abstract

Experiments were performed on ‘Cherokee’ blackberry (Rubus sp.) floral buds and cane tissue collected from field plantings on 12 Jan. and 18 Feb. 1987 to determine the susceptibility of floral primordia, phloem, and xylem to freezing injury after exposure to 16C for 0, 4, 12, 24, or 48 hr. Before rest completion in January, floral primordia, phloem, and xylem subjected to 16C were hardier than those tissues tested in February when rest was completed. Floral primordia and cane tissues dehardened slowly with time at 16C before rest completion. After rest was completed, the rate of deacclimation of floral primordia and xylem increased. Some blackberry canes were subjected to two thawing episodes at 16C for 4 hr. In January, phloem and xylem of canes thawed twice were as hardy or hardier than those tissues in samples thawed once. Conversely, two thawing episodes in February resulted in greater xylem injury than a single episode, but two episodes did not affect the hardiness of the phloem. The number of thawing episodes did not affect floral bud hardiness at either sampling date.

Open Access

Abstract

‘Nittany’ is a ‘York Imperial’-type apple possessing outstanding processing characteristics. Fruit from the original seedling tree has been essentially free of corking; mild corking has been observed in some large fruits from propagules on size-controlling rootstocks. The fruit can be held in refrigerated storage for at least 6 months without appreciable shrinkage or loss of quality. The flesh oxidizes very slowly when exposed to the air and imparts a highly desirable yellow color to processed products.

Open Access

Abstract

Hydrocooling, forced air cooling, and hydrocooling plus forced air cooling techniques reduced the 7/8 mass mean cooling time of packaged potted chrysanthemums (Chrysanthemum morifolium Ramat.) by 57, 43, and 70%, respectively, compared to cooling under normal refrigeration. Mass mean 7/8 cooling time for plants in boxes with 0, 1 or 5 sides exposed to normal air movement in refrigerated storage was 49, 21 and 10 hours, respectively. Plants hydrocooled and stored at 2°C for 0, 5, or 10 days had equal postharvest longevity upon removal compared to plants cooled to 2°C in 60 hours and subsequently stored for the same periods. Plants stored at 22°C displayed equal postharvest longevity after 5 days of storage but were inferior after 10 days storage compared to rapidly cooled plants. Reasons for determining plants inferior varied according to cultivar.

Open Access

Wireless sensor networks (WSNs) transmit sensor data and control signals over long distances without the need for expensive infrastructure, allowing WSNs to add value to existing irrigation systems since they provide the grower with direct feedback on the water needs of the crop. We implemented WSNs in nine commercial horticulture operations. We provide an overview of the integration of sensors with hardware and software to form WSNs that can monitor and control irrigation water applications based on one of two approaches: 1) “set-point control” based on substrate moisture measurements or 2) “model-based control” that applied species-specific irrigation in response to transpiration estimates. We summarize the economic benefits, current and future challenges, and support issues we currently face for scaling WSNs to entire production sites. The series of papers that follow either directly describe or refer the reader to descriptions of the findings we have made to date. Together, they illustrate that WSNs have been successfully implemented in horticultural operations to greatly reduce water use, with direct economic benefits to growers.

Full access

Sweet onions (Allium cepa L.) are typically grown on bare soil and irrigated with high-pressure systems such as sprinklers or center-pivots. The objective of this study was to determine the effects of irrigation system and mulch on bolting, bulb yield and bulb quality over 3 years. The experimental design was a split plot, where the main plot was irrigation system (drip or sprinkler) and the subplot was the type of mulch (bare soil, black plastic film or wheat straw). The results showed that individual bulb weight and bulb yields under drip irrigation were similar to those under sprinkler irrigation. Plants grown on bare soil had the highest total yield during the three seasons and among the highest marketable yield. There were no consistent differences in the bulb number or yield of plants on plastic film mulch compared to those of plants on wheat straw mulch. Plants on wheat straw mulch had reduced foliar nitrogen content. Variability in yields among mulches and seasons was partly explained by changes in seasonal root zone temperature and soil water potential. Total and marketable yields and weight of individual bulbs increased with increasing root zone temperatures up to an optimum at 15.8 °C, followed by reductions in yields and individual bulb weight at >15.8 °C. Onion bolting increased with decreasing foliage nitrogen content, with plants on wheat straw having the highest bolting incidence. Bolting also increased with decreasing root zone temperatures for the season. Total and marketable yields increased with decreasing mean seasonal soil water potential down to -30 kPa. Irrigation system and mulches had no consistent effect on the soluble solids content or pungency of onion bulbs.

Free access

Cucumis sativus L. (cvs. Poinsett and Ashley) plants were grown from seed in a growth chamber at a +10C (28/18) or a -10C (18/28) difference (DIF) between day temperature (DT) and night temperature (NT) on a 12-hour photoperiod for 24 days prior to ozone (O3) fumigation (3 hours at 0.5 umol·mol-1). Negative DIF, compared to +DIF, reduced plant height, node count, fresh weight, dry weight, and leaf area in both cultivars. Photosynthetic rate (Pn), chlorophyll concentration, and variable chlorophyll fluorescence (Fv) were lower and O3 injury and polyamine concentrations were higher at -DIF than at +DIF. Ozone fumigation generally increased leaf concentration of polyamines and reduced Pn, stomatal conductance, and chlorophyll fluorescence. `Poinsett' generally had a higher specific leaf mass and higher concentrations of chlorophyll a and polyamines than did `Ashley', but there was no cultivar difference in O3 injury, growth response, Pn, or stomatal conductance.

Free access

Zoysiagrass (Zoysia sp.) is used as a warm-season turfgrass for lawns, parks, and golf courses in the warm, humid and transitional climatic regions of the United States. Zoysiagrass is an allotetraploid species (2n = 4x = 40) and some cultivars are known to easily self- and cross-pollinate. Previous studies showed that genetic variability in the clonal cultivars Emerald and Diamond was likely the result of contamination (seed production or mechanical transfer) or mislabeling. To determine the extent of genetic variability of vegetatively propagated zoysiagrass cultivars, samples were collected from six commercially available zoysiagrass cultivars (Diamond, Emerald, Empire, JaMur, Meyer, Zeon) from five states (Arkansas, Florida, Georgia, North Carolina, Texas). Two of the newest cultivar releases (Geo and Atlantic) were to serve as outgroups. Where available, one sample from university research plots and two samples from sod farms were collected for each cultivar per state. Forty zoysiagrass simple sequence repeat (SSR) markers and flow cytometry were used to compare genetic and ploidy variation of each collected sample to a reference sample. Seventy-five samples were genotyped and an unweighted pair group method with arithmetic mean clustering revealed four groups. Group I (Z. japonica) included samples of ‘Meyer’ and Empire11 (‘Empire’ sample at location #11), Group II (Z. japonica × Z. pacifica) included samples of ‘Emerald’ and ‘Geo’, Group III (Z. matrella) included samples of ‘Diamond’ and ‘Zeon’, and Group IV (Z. japonica) consisted of samples from ‘Empire’, ‘JaMur’, ‘Atlantic’, and Meyer3 (‘Meyer’ at sample location #3). Samples of ‘Empire’, ‘Atlantic’, and ‘JaMur’ were indistinguishable with the markers used. Four samples were found to have alleles different from the respective reference cultivar, including two samples of ‘Meyer’, one sample of ‘Empire’, and one sample of ‘Emerald’. Three of these samples were from Texas and one of these samples was from Florida. Three of the four samples that were different from the reference cultivar were university samples. In addition, one sample, Empire11, was found to be an octoploid (2n = 8x = 80). For those samples that had a fingerprint different from the reference cultivar, contamination, selfing, and/or hybridization with other zoysiagrasses may have occurred.

Free access