After being interviewed by a newspaper reporter on high tunnels and explaining in great detail what a high tunnel is and how it is different from a greenhouse, you can guess my shock to read the headline “High Tunnels—A Poor Man's Greenhouse.” High tunnels do not offer the precision of conventional greenhouses for environmental control, but they do sufficiently modify the environment to enhance crop growth, yield, and quality and provide some frost protection, but their primary function is to elevate temperatures a few degrees each day over a period of several weeks. In addition to temperature control, there are benefits of wind and rain protection, soil warming, aid in control of insects, diseases, varmints, and birds. They are relatively inexpensive, about $1.30/sq. ft., excluding labor. This system is particularly appealing to new-entry growers with limited capital who utilize retail-marketing channels. High tunnels like plastic-covered greenhouses are generally quonset-shaped with a peak, constructed of metal bows that are attached to metal posts, which have been driven into the ground about 2 feet deep. They are covered with one layer of 6-mil greenhouse-grade polyethylene, and are ventilated by manually rolling up the sides each morning and rolling them down in early evening. There is no permanent heating system, although it is advisable to have a standby portable propane unit to protect against unexpected below-freezing temperatures. There are no electrical connections. The only external connection is a water supply for trickle irrigation.
Vegetables are important in Mexican agriculture, and production under greenhouse conditions has been increased notably during the past year. The production area is about 3500 ha. The main crop grown in greenhouses is tomatoes, but bell pepper is a potential crop due to high yield and that good quality commands a good price during the winter. The objetive of this research was to evaluate nine bell peppers with high technology for horticultural production in the greenhouse. The experiment was carried out at the Experimental Station (INIFAP-CIRNO). The greenhouse conditions are: polyethylene (8 mL), without temperature control, natural ventilation, and soil condition (electrical conductivity of 1.22 dS·m-1and pH 7.96). The planting date was on 26 Oct. 2004. Plant density used was 3.78 plants/m2. The harvest period ocurred from 3 Mar. to 11 May 2005. In this period, we made six cuttings. There were no differences in the yield among varieties. The varieties with the higher yield were Laroles, Asaia, Far-114 and Cupid, with 65.6, 63.1, 63.1, and 57.4 t·ha-1, respectively. Cadia and Parker had the lowest yield, with 78.5 and 90.0 t·ha-1, respectively. The fruit weight was good in all varieties, however, Far-114 and Asaia had higher fruit weight with 272.5 and 269.5 g, respectively. The main insect pests during this experiment were white fly (Bemissia sp.) and leafminer (Lyriomyza sp.). There were no disease problems during this trial.
Weekly records of plant development, daily average temperatures (DAT), and light integrals (DLI) were used to develop a predictive model for time to flower, from seven successive plantings of the new Limonium sinuatum x Limonium perezii hybrid `LSLP4' under two light regimes, full sun or 50% shade. Plantings occurred over the period covering fall through to late spring in a temperature-controlled glasshouse under long days. DLI was highly correlated with the time to visible flower, explaining in excess of 80% of the variation. When combined with the plant growth parameter describing the rate of increase in either leaf number (LNAR) or groundcover index (GCIR), a second model was developed that was able to predict the date of visible flowers of LSLP4 and account for more variation than DLI alone. As a result of the uniformity of temperatures between successive plantings, DAT did not significantly contribute to explaining time to visible flower, but was significant for the period from visible flower through to flower harvest maturity. It is recommended that growers of `LSLP4' for cut flowers can use historical records of DLI to determine planting dates to schedule flowering. Once planting has occurred, by measuring actual DLI, DAT, and leaf number per plant, growers can use the second model to modify the predicted date for visible flowers and flower harvest.
High temperature stress is a major limitation to commercial production of habanero pepper (Capsicum chinense Jacq.) in tropical and subtropical regions. The ability to sustain physiological activity under stress is an important trait for newer varieties. We evaluated leaf thermotolerance [based on the cell membrane stability (CMS) test] of three habanero pepper varieties to: 1) determine genetic variability in CMS among the genotypes studied; and 2) to assess correlations between CMS, photosynthesis and chlorophyll fluorescence [(CF), an indicator of membrane-dependent photosystem II quantum efficiency, ΦPSII]. The genotypes evaluated were TAM Mild Habanero (TMH, a recently developed mild habanero pepper) and its closely related parents (Yucatan and PI 543184). Net CO2 assimilation rate (An) of intact leaves was measured in the field and leaf samples collected and exposed to heat stress (55 °C for 20 min) in temperature-controlled water baths under dim light conditions. The CF was assessed before and after the heat treatment. The CMS was highest in PI 543184, lowest in TMH and intermediate in Yucatan. All genotypes maintained high An rates in the field (25 ± 6 μmol·m-2·s-1); however, correlations between An and CMS were weak. The Φ values were similar among the genotypes (∼0.8) under nonstress conditions, but differed significantly following stress exposure. PI 543184 had the highest post-stress ΦPSII values (0.506 ± 0.023), followed by Yucatan (0.442 ± 0.023) and TMH (0.190 ± 0.025). Observed differences in CMS and ΦPSII indicate plasticity in the response to heat stress among these genotypes.
Mexican production of vegetables under greenhouse conditions has been increased notably during the last year to about 1500 ha. The main crop in greenhouse production is tomato, but european cucumber is a potential crop due to high yield and quality, with a good price in the marketplace and a short growing season. The objective of this trial was to evaluate eight european cucumber varieties and to choose those with high yield and fruit quality, and disease resistance. The experiment was carried out at the experimental station (INIFAP-CIRNO). Greenhouse conditions were: polyethylene (8.0 mL), without temperature control; natural ventilation; and soil with electrical conductivity of 1.22 dS·m-1 and pH 7.96. Sowing date for seed was 15 Oct. 2004. Plant density was 3.78 plants per m2. The harvest period was 26 Dec. 2004 to 11 Mar. 2005, with an average of 10 cuttings. Varieties with highest yield were `Imanaol', `Bermejo', `Dominica', and `Kalunga', with 18.9, 15.2, 14.8, and 14.3 kg·m2, respectively. Fruit quality was excellent in all varieties; however, `Imanaol' had the highest percentage of size and fruit number. The main insect pest during the year was white fly (Bemissiasp.) and the most important disease was powdery mildew (Erishipecichoracearum).
Chlorophyll fluorescence was measured under both laboratory and greenhouse conditions in an effort to develop a quick, reliable, and inexpensive laboratory procedure capable of predicting heat stress experienced by tomato (Lycopersicon esculentum Mill.) under greenhouse conditions. The laboratory tests consisted of measurements of the ratio of variable to maximal chlorophyll fluorescence (Fv/Fm) performed on leaf discs taken from whole tomato leaves and placed on a temperature controlled plate. Comparisons were made with greenhouse measurements of the same parameter conducted on intact leaves of whole plants exposed to different temperature treatments imposed by manipulation of the aerial environment of the greenhouse. Dark adaption periods ranging from 15 min to all day in the greenhouse and temperature exposure periods ranging from 5 min to 60 min in the laboratory were compared to find the best correlation between the two tests. Best agreement was obtained with 60 min treatment times in the laboratory and 60 min dark adaption periods in the greenhouse. Fv/Fm decreased quadratically with increasing leaf temperature in a similar fashion in both tests, suggesting that the laboratory approach can adequately predict plant response to greenhouse heat stress.
Greenhouse and field methods were developed to screen Allium spp. for resistance to Botrytis leaf blight (caused by Botrytis squamosa Walker). In the green-house, plants were sprayed with laboratory-grown inoculum and incubated in a temperature-controlled enclosure containing an atomizing mist system. For field inoculations, a portable misting system with windbreaks was erected, and the plants were sprayed with laboratory-grown inoculum. Greenhouse and field incubation conditions maintained leaf wetness without washing inoculum from the leaves. Botrytis leaf blight symptoms in greenhouse and field evaluations were identical to symptoms in commercial onion fields. A total of 86 selected USDA Allium collection accessions were evaluated using these methods. All A. fistulosum accessions and A. roytei were highly resistant to immune, as were most accessions of A. altaicum, A. galanthum, A. pskemense, and A. oschaninii. Nearly all of the A. vavilovii and A. cepa accessions were susceptible. However, one A. cepa accession (PI 273212 from Poland) developed only superficial lesions, which did not expand to coalesce and blight leaves. This work confirms previous reports of Botrytis leaf blight resistance in Allium spp., and suggests that strong resistance exists with A. cepa.
The effect of root zone temperature (temp.) on 18-month-old plants of `Gulf Coast' blueberries (predominantly Vaccinium corymbosum L.) grown in temperature-controlled water tanks during Summer 1993 were determined for plant growth and leaf nutrient status. Soil medium (1 sand: 1 peat, v/v) was maintained at or above –20 k Pa. Six singleplant replicates were placed in either a 24 or 31C tank. After 60 days, plants grown at 24C had more leaves, greater total leaf area, and higher leaf and stem fresh weight. Leaf moisture (P < 0.09) and stem dry wt (P < 0.07) were greater at the lower root temp. Root: shoot ratio and total root dry weight were not affected by root temp. Leaf S and Cu levels were higher and NO3 levels lower in plants grown at the 24C root temp. compared to those grown in the 31C root temp. Nitrogen, K, Na, Ca, Mg, P, Fe, Mn, and Zn (order of decreasing concentration) were not affected by root temp. The total N: NO3-N ratio was higher at the lower root zone temp.
Studies were conducted with Physocarpus, Weigela, Hibiscus, Euonymus, Forsythia, Spiraea, Lonicera, and Taxus to evaluate the effects of warming temperatures on shoot dehardening. Container-grown plants were stored pot-in-pot, allowing shoots to receive natural outdoor conditions until early March. Control plants remained at 0C (32F), while treatment plants were placed in a temperature-controlled chamber at 21C (70F) and given up to 8 days of warming. Controlled-temperature freezing was used to evaluate plant hardiness. Hardiness levels of Weigela, Spiraea, and Forsythia rapidly decreased after 1 day of warming and again after the 7th day. Hibiscus gradually decreased in hardiness until the 7th day. The influence of polyhouse storage, in which plants were stored pot-in-pot, on the dehardening of Weigela, Hibiscus, and Euonymus was compared to outdoor storage, where plants were stored pot-in-pot. The warming effects of the polyhouse decreased the cold hardiness of the species studied. Results of the warming effects will be presented.
A study to determine the influence of light duration on seed germination was performed in a temperature-controlled growth chamber. Light treatments consisted of 0 (control), 6, 8, 10, 12 and 14 h of light exposure. Cool fluorescent light bulbs provided 19 μMol·m-2·s-1 light. Fifty seeds of each treatment were placed into separately labeled 6.0-cm-diameter petri dishes lined with Whatman #42 filter papers moistened with 2 mL of distilled water. Seed of both species germinated poorly in the control treatment. Mean time of germination (MTG) and germination percentage increased for both species when seeds were exposed to light. Pre-soaking seed in gibberellic acid (GA) significantly improved germination percentages of both species compared to the untreated control. Centipedegrass germination percentage and MTG also increased with light exposure. Carpetgrass seed germination was not enhanced by GA treatments with light exposure. The results of this experiment suggests that, if seed are covered too deeply, excluding light, MTG and percentage germination will be reduced. However, pre-soaking seed in a GA solution can improve dark germination by as much as 50% for both grass species.