Unheated Plastic Greenhouse Research Articles

Assessment of Agronomic Traits and Essential Oil Yield in Various Local Mint (Mentha piperita L.) Genotypes

Objective: Mentha piperita L. has long been used in medicine, pharmaceutical industry, food and cosmetic industries due to the bioactive compounds it contains. This study was carried out to determine some agronomic characteristics and essential oil yield of mint genotypes collected from different regions of Ordu province. Materials and Methods: A total of 44 different genotypes collected from 16 different districts of Ordu province were used in the study. Rooted mint cuttings were grown in unheated plastic greenhouse in balcony type plastic pots. Mint plants were harvested in 3 different periods and shoot length, leaf width, leaf length, colour characteristics, leaf chlorophyll index, total yield and essential oil yield were determined. Principal component analyses were performed using the data obtained from these traits. Unweighted pair group method algorithm (UPGMA) clustering analysis was performed using Euclidean similarity distance and dendrograms of genotypes were formed. Results: At the end of the study, plant length was 12.2-60.6 cm, leaf width 0.8-4.3 cm, leaf length 1.2-9.8 cm, leaf chlorophyll index 4.75-47.8 cci (SPAD), essential oil yield 0.45-2.9% and total yield 0.1-4.2 t da-1 in mint genotypes. As a result of the principal component analysis, the eigenvalues of the first 4 principal component axes were found to be greater than 1. The first 3 axes have high variation percentage compared to other axes. Mint genotypes were divided into 2 main groups and 4 subgroups in the UPGMA dendrogram. While G12 and G33 were the closest mint genotypes, G10 and G11 were found to be genetically distant genotypes. Conclusion: In the study, genotypes that exhibit potential in terms of total yield and essential oil yield have been identified. As a result of the research, agronomic characteristics and essential oil ratios of different mint genotypes were determined and qualified genotypes that can be material for future breeding studies were determined.

The Impact of Salinity in the Irrigation of a Wild Underutilized Leafy Vegetable, Sonchus oleraceus L.

Introducing non- or under-utilized crops to cultivation generates benefits such as biodiversity enrichment, supporting mitigation actions towards climate change-induced effects. The salinization of soil and water supplies is progressively disrupting natural habitats and food production, especially in regions such as the Mediterranean. Sonchus oleraceus L. is a Mediterranean wild leafy green with nutritional and medicinal properties. This study's purpose was to determine whether salinity affects the growth, quality, and nutrient composition of Sonchus oleraceus L. In an unheated plastic greenhouse, seedlings were transplanted in pots filled with perlite and irrigated with a nutrient solution with no NaCl added (the control, C) or with the addition of 40, 60, 80, and 100 mM of NaCl (treatments S4, S6, S8, and S10, respectively). The leaf and root growth, leaf quality, and the nutrient composition of leaves and roots were determined. Regarding the results, growth was mainly affected at high salinity levels (S8 and S10), with no observed effects of salinity on the determined quality parameters. The nutrient composition was variably affected by salinity in leaves but not in roots (except in the case of Na and the K/Na ratio). Sonchus oleraceus L. showed a general relative tolerance in moderate salinity levels (40 and 60 mM of NaCl), suggesting potential commercial exploitation of the species in areas where the quality of irrigation water is low. However, the health effects of consuming this species grown under salinity stress need to be studied in future research.

Modifying the Growing Media and Bio Stimulants Supply for Healthy Gerbera (Gerbera jamesonii) Flowers

AbstractGerbera (Gerbera jamesonii) cv. Jaguar Yellow is an ornamental plant of the Asteraceae family. Ordinarily, farmers use expensive materials such as peat moss as a media substrate in gerbera production, in addition to application high nitrogen fertilizers. Therefore, the current study was designed to assess the yield and quality changes of gerbera flowers owing to utilizing environment-friendly inputs under unheated plastic greenhouse conditions for two seasons of 2017/18 and 2018/19. The experiments were laid out in a randomized complete block design with 3 replicates, each replicate involved 5 pots per treatment. For preparing the soil substrate mixtures, four substances were used which involved peat moss (P), sand (S), vermicompost (V), and compost (C). P + S, P + S + V and P + S + C were assembled whether with or without Azotobacter+Azospirillum as bio stimulant (Bio) addition to obtain six combinations. Results showed that P + S + V + Bio was the effective practice for enhancing gerbera plant height, leaf width, root weight plant plant-1 and leaves weight plant-1. Also, P + S + V + Bio produced the maximum values of leaf chlorophyll, nitrogen, phosphorus, and potassium contents. The differences in flowering initiation between P + S and each of P + S + V, P + S + V + Bio, P + S + C and P + S + C + Bio were not significant. P + S + V + Bio (for flowering duration and flower yield), in addition to P + S + V (for flowering duration) recorded the highest values in both seasons.

Biostimulants as a Means to Alleviate the Transplanting Shock in Lettuce

When transplanting vegetable plants in the field, the transplants undergo a small or large setback in growth, known as transplanting shock. Various practices are commonly applied to reduce the transplanting shock. In the past two decades, several studies have shown that the application of microbial and non-microbial biostimulants can enhance plant tolerance against abiotic stresses. However, there is no information on the effect of applying biostimulants at the time of transplanting in mitigating the transplanting shock of lettuce transplants in the field. Lettuce seedlings transplanted into the soil of an unheated plastic greenhouse were treated with two biostimulants, one microbial (Bactiva®) and one non-microbial (Isabion®), on the day of transplanting and after 14 and 21 days. During production, plant growth, and development, chlorophyll fluorescence and compositional parameters were determined. According to the results, the application of the non-microbial biostimulant had a significant effect on some measured parameters, with the leaves of the treated plants having a higher chlorophyll index (CCI) by 8%, as well as higher fluorescence parameters Fm/Fo, Fv/Fo, and Fv/Fm and area by 7, 10, 3, and 27%, respectively, but fewer total soluble phenols and lower fluorescence parameter ABS/RC by 7 and 26%, respectively, compared to the control untreated ones. The above may constitute some effects on the transplanting shock, without, however, being accompanied by significant effects on the number of leaves/plant, the leaf color parameters (L*, a*, b*, C*, and ho), and the chlorophyll (a, b, a + b), total carotenoid, dry matter, and nitrate content, along with the antioxidant capacity and plant fresh weight at harvest. However, a notable effect was that a greater percentage of plants at harvest had a fresh weight in the 351–400 class, while the greatest percentage of the control plants had a fresh weight in the 301–350 g class. In contrast, the application of the microbial biostimulant had no significant effect on any of the parameters determined compared to the control. Therefore, under the conditions of the present study, the effectiveness of biostimulant application at the time of transplanting on lettuce transplants is questionable.

Mitigation of Chilling Stress by Ozone Pretreatment and Acclimation of Sweet Pepper Grown under Unheated Greenhouse Conditions

Ozone is an important air pollutant that causes many challenges for human health, such as lung diseases. The negative impacts of exogenous ozone on cultivated plants have been discussed in several publications, but the positive impacts are less investigated. The current study is an attempt to answer the following question: is there any positive contribution of ozone pretreatment in growing plants under stress? Plants grown in unheated plastic greenhouses suffer from cold stress during the winter when the temperature drops to 5–10 °C. This stress can also be enhanced under saline soil conditions in arid regions. Treatments involving different ozone application methods (seed priming and seedling foliar application) and cold pretreatment (4 °C for 36 h) were compared with untreated controls of two sweet pepper hybrids (Zidenka and Lirica) in an unheated plastic greenhouse. In general, the Lirica hybrid outperformed the Zidenka hybrid in growth and fruit yield and showed good adaptation to cold stress resulting from ozone treatment through foliar application on seedlings. Moreover, cold treatment was associated with higher values of the studied parameters compared to the control (untreated). A concentration of 20 ppm of ozone in the first season and as 30 ppm of ozone in the second season increased plant leaf area, proline content, and APX activity, all of which improved the plant’s defense mechanisms against cold stress. These benefits contributed to high fruit sets; early, total, and marketable fruit yields; and fruit quality under cold stress. The highest yield (16.52 kg m−2) was attained with 30 ppm ozone applied as a seedling spray, compared with 10.07 kg m−2 in the control. Therefore, the foliar application of ozone up to 30 ppm can be recommended for sweet pepper hybrids of Lirica under unheated plastic greenhouse conditions. Further investigations are needed to study the interaction of combined ozone and cold stress, as well as various levels of soil salinity.

The concept of introduction and breeding of non-traditional vegetable plants in Siberia

The introduction of new vegetable crops in the harsh climate of Siberia presupposes the evaluation of resistance to environmental factors (long day, low temperatures, fungal diseases etc.) limiting the growth of plants, using pre-breeding methods.The studies were carried out in the outdoor and unheated plastic greenhouse conditions of the Central Siberian Botanical Garden (CSBS), Novosibirsk (54 ° N 83 ° E) and in the outdoor and the conditions of phytotron of the N.I.Vavilov All-Russian Institute of Plant Genetic Resources (VIR). We used a large collection of species accessions belonging to families Leguminosae, Cucurbitaceae and Brassicaceae. It is proposed to use the taxonomically important, stable traits and other features that affect the possibility of scaling up the cultivation of crops in Siberia. Sequential assessment, e. g. asparagus bean includes evaluation of resistance to a long day, cold resistance in the phase of mature male gametophyte in vitro, the composition of pathogenic micromycetes, and the resistance of accessions to them. Also, it is offered to use the symbiotic systems, including the effective strains of Bradyrhizobium sp. and high-yield cultivars with a neutral response to day length and low variation in biochemical composition, for example, the cultivar ‘Sibirskiy razmer’ bred in the CSBS.

Effect of Growing medium, Fertilization and Biostimulant treatments on Growth and Flowering of Potted Gerbera (Gerbera jamesonii cv. Jaguar Yellow)

The current study was aimed to investigate the effect of different fertilization and biostimulant treatments on growth and flowering of Gerbera (Gerbera iamesonii cv. Jaguar Yellow) plant under unheated plastic greenhouse conditions. This study was carried out for two successive seasons of 2016/2017 and 2017/2018 at the farm of the Arid lands Agriculture graduated studies and Research Institute (ALARI), Shobra Elkheima area, Qalyobia governorate, Egypt. The experiment were laid out in a completely randomized design (CRD) with 3 replications, and the end results have been subjected to analysis of variance (ANOVA). Freshly extracted gerbera seedling have been planted into pots filled with peatmoss + sand (1:1), peatmoss + sand + vermicompost (1:1:1), peatmoss + sand + compost (1:1:1) with or without 250ml of Azotobacter + Azospirllum mixture, as biostimulant, and slow-release NPK (4.2g) or fast-release NPK (2.5g) fertilizers to each plant, to determine the effect of fertilizer, biostimulant and growing medium types on the production of potted gerbera. Growth and flowering characteristics were measured. Results indicated that medium combination of sand + vermicompost + peatmoss (1:1:1) with biostimulant, regardless of the fertilizer type, gave significantly increased results in all measurements, compared to all other combinations. Plants grown in medium supplemented with biostimulant and fast-release fertilizer, gave flowers with good qualities While the medium combination sand + vermicompost + peatmoss (1:1:1) with biostimulant in combination with either one of NPK mineral fertilizers (fast-release fertilizer and slow release fertilizer) gave significantly increased results in most parameters, shown in higher total vegetarian and quality when combined with slow release fertilizer than fast-release fertilizer. Under this treatment, plant length was (28.2 cm), number of leaves per plant was (24.8), stem diameter was (3.7 mm), fresh weight (47.9 g), seedings dry weight (12.5g), length of the longest tap root was (19.8 cm), diameter of tap root (2.9 mm), number of secondary roots (40.7), root/shoot ratio (2.57), Leaf greenness SPAD 59, and the highest number of daughter plants (5.3/plant). These records were all significantly higher than other treatments

Indicadores para evaluar el desempeño en el uso del agua, energía y mano de obra en un invernadero de baja tecnología

One of the advantages of controlled agriculture is the notable increase in crop yields. However, at high-tech levels, water use productivity has increased, while energy use productivity has decreased. Therefore, the objective of this study was to estimate water, energy and labor use productivity in tomato cultivation, for a low-tech greenhouse. The inputs used in the production process were recorded from April 24 (date of transplant) to October 16, 2016 (date of last harvest). The yields obtained were 19.07 kg∙m-2. Water use productivity was 27.86 kg∙m-3 (35.89 L∙kg-1), which is within the range reported for unheated plastic greenhouses (30-40 L∙kg-1). Energy productivity was 0.331 kg∙MJ-1, and the energy consumed per unit area was 57.61 MJ∙m-2, with Calcium nitrate being the input with the highest energy demand (49.49 %). During the production cycle, 738 working hours were used, 78 % of which were dedicated to cleaning and maintenance, with labor productivity of 3.02 kg∙h-1.

Effects of gravel mulch on surface energy balance and soil thermal regime in an unheated plastic greenhouse

This work analyses how a mulch layer of mostly gravel particles affected the soil thermal dynamics in an unheated plastic greenhouse in a Mediterranean area (South-East Spain), where suboptimal regimes of soil temperature usually prevail in winter crop cycles. Soil temperature and heat flux profiles were measured in two soil types: (i) a 0.1-m thick gravel mulch (GM) placed at the top of a 0.30-m layer of imported loamy soil and (ii) the latter without gravel mulch (NM). These measurements were conducted during a winter period (14–28 January) when the dominant source of energy in the soil root-zone was the heat from deeper soil layers. The higher albedo of the GM and its higher long-wave radiation losses reduced substantially the daily net radiation at the mulch surface by ca. 77% with respect to NM. However, the soil root-zone maintained warmer under the GM than with NM in a period when soil temperatures are usually below the optimum. This was mainly caused by the insulating property of the mulch, which acted as heat barrier and increased the resistance to heat transmission from deep soil horizons towards the surface. This passive heating of the soil root-zone by using a gravel mulch was later confirmed in a summer–winter cycle of sweet pepper grown in an unheated plastic greenhouse. The gravel mulch also reduced the soil evaporation and increased the reflected short-wave radiation towards the plants, but the air temperature above the mulch fluctuated more strongly than in the absence of the mulch.

Influence of Pre-Harvest Factors on Postharvest Quality of Fresh-Cut and Baby Leafy Vegetables

Shelf life of horticultural commodities is dependent on postharvest handling but also on a wide range of pre-harvest factors, which include genetic and environmental parameters. This study was conducted to explore the influence of cultivar, leaf position, and piece position on the leaf on visual quality of fresh-cut butterhead lettuce as well as the effect of a wide range of cultivation seasons on the postharvest quality and shelf life of baby leaves (spinach and ‘wild’ rocket). Six butterhead lettuce cultivars were used (cultivated soilless in an unheated plastic greenhouse) while the effect of leaf position on the plant (outer and inner leaves) and the piece position on the leaf (piece one close to the leaf base and piece four close to the top) were also evaluated. Baby leaves were cultivated under an unheated plastic greenhouse for winter production and under a nethouse for the rest of the growing season, with a total of five and seven sampling dates for spinach and ‘wild’ rocket respectively. The cultivar of butterhead lettuce had a significant effect on postharvest quality of fresh-cut product but more important was the piece position on the leaf. When this was closer to the base of the leaf, there was more browning on cut edges and limited shelf life for the fresh-cut lettuce. The result was associated in one tested cultivar with PAL activity, which was higher by 106% for piece one compared to piece four as an average for the whole storage period. The growing season of baby leaves had a great impact on their shelf life, with the season of mild environmental conditions achieving the highest marketability.

Water use and crop performance of two wild rocket genotypes under salinity conditions

In literature, the parameters of salinity tolerance of the main cultivated species are known, but are missing for many minor species such as wild rocket, whose cultivation in many areas of southern Italy affected by salinity is growing. Therefore, a research has been carried out i) to evaluate the response to salinity in water use, water use efficiency, yield characteristics and morfological features, and ii) identify the salinity tolerance parameters of two genotypes of wild rocket: Diplotaxis tenuifolia (L.) DC and D. muralis (L.) DC. The study was carried out in the spring of 2007 and 2008 in Policoro (MT), southern Italy, under unheated plastic greenhouse conditions. Wild rocket was sown in plastic pots containing 20dm3 of soil. For each genotype, six soil salinity levels were compared, obtained by accurately mixing before sowing the soil with 0.0, 0.5, 1.0, 2.0, 3.5 and 5.5gdm−3 of NaCl+CaCl2 1:1 (on a weight basis). Irrigation was performed with fresh water having electrical conductivity of 0.5dSm−1. In each year, 3 harvests were performed; water use and the main production and plant growth parameters were recorded. D. tenuifolia provided a yield 47.3% higher than D. muralis. By rising salinity, progressive decline in marketable yield and growth of the leaves was recorded, while the dry matter content increased. The increase in salinity has led to the progressive reduction of water use in both genotypes. From moderate salinity values (about 5.5dSm−1), the reduction in yield water use efficiency as a result of increased salinity has been observed. In addition, salinity reduced specific leaf area and increased leaf succulence. Both genotypes rank among moderately salt sensitive species, according to Maas and Hoffman's model (1977). However, D. tenuifolia, with a critical threshold of 1.98dSm−1 and a slope of 6.61%mdS−1, showed a slightly higher tolerance than D. muralis (threshold 1.34dSm−1 and slope 7.25%mdS−1). Reduction in yield due to salinity occurred mainly for the decrease in leaf size and, secondly, number of leaves.

The Use of Chemicals with Specific Mode of Action in an Integrated Control Program on Eggplant for the Greenhouse Whitefly, Triαleurodes vαporαriorum

In the unheated plastic greenhouses of Crete, the control of the greenhouse whitefly Trialeurodes vaporariorum Westwood using chemicals is usually needed during winter time. The systemic insecticide Vydate when applied as soil granules at the highest dose (2g/plant), gave protection for young eggplants against whitefly for a period of 5 weeks. Experiment with different chemicals showed that the new insect growth regulator Nomolt, is fairly effective in controlling the greenhouse whitefly when used in combination with Actellic. It gave equally good results when compared with a mixture of Applaud and Actellic.

Greenhouse cultivation of banana: very favorable crop in Turkey

The present study evaluated plant morphological traits and fruit quality parameters of banana 'Dwarf Cavendish' cultivar and local type 'Azman' grown in subtropical conditions, under unheated plastic greenhouse. The study was conducted between 2014 and 2015 in Alanya, the province of Antalya. The planting density was 1850/ha and drip irrigation system was used. Plant morphological features (plant height, stem circumference and height, leaves retention at flowering and bunch stalk circumference), yield components (number of hands, number of fingers, finger circumference and length, and bunch weight) and fruit quality attributes (peel thickness, the peel and pulp ratio, soluble solid content) after ripening were determined. The plant height, stem height, number of hand, bunch weight and finger features were the most variable traits. 'Dwarf Cavendish' produced shorter plants and pseudostem height. Bunch weight and finger features in 'Azman' were found to be superior to 'Dwarf Cavendish'. As 'Azman' type produced higher yield (69.3 t/ha/year) than 'Dwarf Cavendish' cultivar (52 t/ha/year), this local type is recommended for cultivation under unheated greenhouse.

MODELING UNCERTAINTY OF GREENHOUSE CROP LETTUCE GROWTH MODEL USING KALMAN FILTERING

The NICOLET model was developed to predict biomass growth and nitrate content of a greenhouse lettuce crop. However, several studies have shown that accurate prediction of nitrate concentration is rather difficult, due to cultivar differences and its sensitivity to changes of the environment. The present work explores possibilities of improving the prediction performance of the NICOLET model by incorporating information (data assimilation) coming from samples of destructive measurements of an actual crop. A lettuce crop was grown from March to May 2008 in a hydroponic system inside an unheated plastic greenhouse located at the University of Queretaro, Mexico. Air temperature and humidity, solar radiation and also carbon dioxide inside the greenhouse were measured at the center of greenhouse and recorded in a data logger every 5 min. At regular intervals a variable number of lettuce plants were harvested in order to measure both fresh matter and dry weight per plant, leaves nitrate content and plant leaf area index. The parameters of the NICOLET model were estimated with the mean data coming from the sampled plants. The unscented Kalman filter (UKF) was selected as assimilation method. Simulation results were improved by using the measured data on a different data set that the one used for parameter estimation. The filters estimated properly the state variables, thus significantly improving the model fitting in comparison with the simulation without data assimilation. The results suggest that Kalman filtering is a suitable method to provide the required automatic adaptation to time-varying phenomena in complex crop models.

Application of β-naphthoxyacetic acid ( β-NOA) improves fruit yield and marketable quality in out-of-season cherry tomatoes (Solanum lycopersicum L. var. cerasiforme (Dunal) D. M. Spooner, G. J. Anderson and R. K. Jansen) cultivated in unheated greenhouses in the Mediterranean Basin

SummaryThe effects of truss vibration, and the application of β-naphthoxyacetic acid ( β-NOA) to flowers, on fruit-set, total and marketable yields, and fruit quality were studied in two cherry tomato [Solanum lycopersicum L. var. cerasiforme (Dunal) D. M. Spooner, G. J. Anderson and R. K. Jansen] hybrids ‘Conchita F1’ and ‘Cherelino F1’, grown in an unheated plastic greenhouse during the Winter/Spring and Spring seasons in Southern Greece. Fruit-set was high in the Winter/Spring crop but, due to unfavourable conditions (i.e., night-time temperatures below 10ºC, which impaired microsporogenesis, pollination, and fertilisation), most fruit contained few seeds, were small and unmarketable. Although both truss vibration and β-NOA significantly increased mean fruit weights, and total yields, in both cultivars, the application of β-NOA gave the greatest increase in mean fruit weight and percentage of marketable fruit. In contrast, in the Spring crop, neither treatment affected the number or weight of fruit per plant because the climatic conditions were more favourable for pollination and fertilisation. The application of β-NOA did not adversely affect fruit quality, as previously reported in large-fruiting tomato cultivars. β-NOA did not induce any malformation or puffiness in the fruit and, while these seedless fruit showed higher dry mass percentages, higher total soluble solids contents, and lower titratable acidity levels than seeded tomato fruit, their colour, firmness, sugar, and phenolics contents were not affected. Conditions that are unfavourable for fruit set frequently occur in unheated greenhouses in the Mediterranean Basin during the Winter and early Spring; therefore, we conclude that the application of β-NOA to the flowers of cherry tomato at that time will ensure higher yields, better market quality, and higher market returns.

Effect of grafting on yield and quality of eggplant (Solanum melongena L.)

Environmental conditions and growing techniques may influence the characteristics of eggplant fruits and their content in phenolic compounds. Grafting is a non chemical alternative for overcoming the effects of intensive and continuous cropping that can modify plant and fruit characteristics. The rootstocks preferred for eggplant are hybrids of tomato or tomato KVFN. Also species taxonomically close, as Solanum torvum, have been used and showed good vigour, compatibility and resistance to wilt disease. Information on yield and quality of grafted eggplants onto this rootstock is conflicting. Therefore, the aim of this study was to evaluate yield and quality of eggplant cultivars (Birgah, Black Bell, Black Moon and Longo) grafted or ungrafted onto Solanum torvum. Plants were grown from October 2009 to May 2010 in an unheated plastic greenhouse on solarized soil. Grafted plants had lower mortality, while yield and quality of fruits were mostly influenced by cultivars. The differences recorded for growth and yield of the tested cultivars might be due to different growth characteristics, graft affinity and compatibility. Longo and Black Moon were not influenced by grafting, while grafted plants of Birgah and Black Bell had a higher unmarketable production. Grafting onto Solanum torvum changed the color of fruits that were darker and with a less vivid color. Browning of inner tissue was not influenced by grafting. Total phenolic content was greater in the ungrafted plants.

LEAF AND BUD TEMPERATURES OF SOUTHERN HIGHBUSH BLUEBERRIES (VACCINIUM CORYMBOSUM) INSIDE HIGH TUNNELS

A high tunnel is a passively heated and cooled plastic-covered greenhouse used for season extension and crop protection for a variety of horticultural crops, including southern highbush blueberry (Vaccinium corymbosum L.). Frost protection remains a major challenge for early-season blueberry production, due to poor heat retention by high tunnels. Understanding the energy balance of high tunnels is essential for predicting night-time minimum temperatures and implementing frost protection strategies. We determined the effects of high tunnels on air, leaf, and bud temperatures of southern highbush blueberry. Impacts of frost blankets (one frost protection strategy) on temperatures were also explored. High tunnels quickly warmed during the day but cooled to ambient or below ambient air temperature at night, particularly during clear days and nights. Leaf and bud temperatures in high tunnels were higher than those of outdoor plants during the day but lower during night. The presence of a frost blanket reduced night-time radiative cooling of leaves and buds and allowed their temperatures to stay closer to ambient conditions inside of high tunnels. Lack of night-time heat retention in high tunnels was likely due to the properties of the polyethylene greenhouse cover, lack of ventilation, and large surface area to volume ratio of the high tunnels. INTRODUCTION A high tunnel is an unheated plastic greenhouse that is passively ventilated and can be erected over large areas (Lamont, 2003). They lend themselves well to organic horticultural practices and are becoming indispensable components of many organic farms. Blueberries are an economically significant crop for Georgia and production of out-of-season organic blueberries in high tunnels could be a financially lucrative endeavor for Georgia’s growers. The research reported here was part of a larger project to examine the feasibility of production of early organic southern highbush blueberries inside of high tunnels in Georgia (USA). The main goal of the overall research project was to discover the ideal date of closing high tunnels to achieve both early and high blueberry yield. In the first year of this project, we found that increased daily maximum air temperatures inside high tunnels facilitated early flowering, fruiting, and onset of vegetative growth (Ogden et al., 2007). The major limitation of the high tunnels was their inability to retain heat during cold nights. Night-time minimum air temperatures inside the high tunnels were equal to or lower than outside air temperatures (Ogden and van Iersel, 2008). Likewise, Montero et al. (2005) reported that the air in unheated greenhouses was about 2.5°C cooler than the outside air. The lack of frost protection provided by the high tunnels necessitated the use of propane heaters on nights with minimum temperature below 0°C to protect the developing, freeze sensitive flowers and buds. The research reported here was conducted during the second year of this project. In an effort to reduce fuel costs, we also experimented with frost blankets on nights with predicted lows of 0 to -1°C during the

Desempenho de cultivares de tomateiro em sistema orgânico sob cultivo protegido

A agricultura orgânica no Brasil cresce a taxas superiores a 30% ao ano, devido principalmente à maior conscientização dos consumidores que buscam alimentos saudáveis, livres de resíduos químicos e biológicos. Dentre as hortaliças cultivadas em sistema orgânico, o tomate constitui grande desafio para os produtores devido à inexistência de recomendações de manejo cultural e de cultivares desenvolvidas específicas para esse sistema de cultivo. Diante disso, o presente trabalho teve como objetivo avaliar o desempenho de cultivares de tomate sob sistema orgânico, em ambiente protegido. O experimento foi conduzido de maio a outubro de 2004 em campo, no município de Araraquara-SP. O delineamento experimental adotado foi blocos ao acaso, com quatro repetições e oito tratamentos (cultivares Avalon, Colibri, HTX-5415, HTX-8027, Sahel, San Marzano, San Vito e Jane). As plantas foram conduzidas em fileiras duplas, com duas hastes por planta no espaçamento de 0,8 m entre linhas e 0,6 m entre plantas (cerca de 20.000 plantas ha-1), sem poda apical. O híbrido Sahel destacou-se com o melhor desempenho para rendimento comercial. A traça-do-tomateiro se revelou como fator limitante à produção de tomate em sistema orgânico, sendo responsável, em média, por 17% de danos nos frutos colhidos das oito cultivares que foram avaliadas.

Use of stem diameter variations to detect plant water stress in tomato

The sensitivity of stem diameter variations (SDV) measured with linear variable transducer (LVDT) sensors as indicators of plant water status in tomato was evaluated. Two tomato crops were grown sequentially in a sandy loam soil in an unheated plastic greenhouse. These were an autumn–winter tomato crop (autumn crop) and a spring–summer tomato crop (spring crop). One drying cycle of 61 days was imposed to the autumn crop in winter at 92 days after transplanting (DAT). Two drying cycles, each of 29 days, were applied to the spring crop, to young (58 DAT) and mature plants (121 DAT). For each drying cycle, four replicate plots did not receive irrigation, and four were well watered. During each drying cycle, LVDT sensors continuously measured SDV, and daily measurements were made of leaf (Ψ leaf) and stem water potential (Ψ stem). SDV data was interpreted using the SDV-derived indices, maximum daily shrinkage (MDS) and stem growth rate (SGR). The response of SDV-derived indices to water deficit differed with (1) climatic conditions during stress imposition and (2) crop age. In the winter drying cycle of the autumn crop, the responses of the SDV-derived indices to soil drying were relatively small and slower than Ψ leaf and Ψ stem. Under warmer conditions, the SDV-derived indices were much more responsive to soil drying. In rapidly growing young plants, where SDV was characterized by high SGR and small MDS, SGR was the most sensitive SDV-derived index. In more mature plants with little stem growth, MDS was the most sensitive SDV-derived index. In mature plants grown in warm to hot conditions, MDS (1) responded at a similar time or earlier than Ψ leaf and Ψ stem and (2) had larger “signal” values (ratio of values from unwatered to control plants) than Ψ leaf and Ψ stem. However, there was appreciably more “noise” (coefficient of variation, CV) associated with the SDV-derived indices, giving lower “sensitivity” values, determined from “signal” to “noise” ratios, than for Ψ leaf and Ψ stem. Regression analysis between MDS of well-watered plants and climatic variables gave best results for a linear relationship between MDS and daily maximum vapor pressure deficit. There were strong linear relationships between MDS and Ψ leaf for each drying cycle. The slopes of these relationships differed with crop age indicating that there was no constant relationship between MDS and Ψ leaf for a whole season. Overall these results demonstrated that MDS and SGR can be sensitive indicators of the water status of tomato crops under conditions of moderate to high evaporative demand. However, the variability associated with the SDV-derived indices and the changing MDS–Ψ leaf relationship with crop age represent major issues regarding the development of irrigation scheduling protocols for tomato.

Response of stem diameter variations to water stress in greenhouse-grown vegetable crops

SummaryThe ability of indices derived from stem diameter variations (SDV) to detect water stress in vegetable crops grown under greenhouse conditions was evaluated. Two crops, an Autumn-Winter pepper crop and a Spring-Summer melon crop, were grown in soil, in an unheated plastic greenhouse with drip irrigation, in conditions similar to commercial production. A pot study with pepper was also conducted during Autumn-Winter. In each study, two drying cycles were imposed for 7–21 d during the fruit production stage, and un-watered plants were compared with well-watered plants. During each drying cycle, linear variable displacement transducer (LVDT) sensors were used to measure SDV continuously, and daily measurements were made of leaf ( leaf) and stem water potential ( stem). Several indices derived from SDV measurements, including maximum daily shrinkage (MDS) and daily stem diameter growth rate (SGR) were evaluated. In the drying cycles of soil-grown pepper, conducted during Winter, under climatic conditions of low evaporative demand, SDV-derived indices were unaffected by 20-21 d of soil drying, despite both stem and leaf being moderately affected. Pepper plants grown in pots under very similar climatic conditions had appreciable and rapid responses in SDV-derived indices, with MDS increasing and SGR decreasing. In the drying cycles of soil-grown melon, imposed during the relatively higher evaporative demand conditions of Spring and Summer, MDS responded earlier and had larger “signal” values (ratio of values from un-watered to control plants) than leaf or stem. However, there was more variation associated with MDS. In melon, there were strong linear relationships between MDS and both leaf and stem. The present study suggested that SDV-derived indices can be sensitive indicators of plant water status in melon and pepper when grown (a) in pots with a restricted root volume under any climatic conditions, and (b) in soil during periods that do not include climatic conditions of low evaporative demand.