Unheated Glasshouse Research Articles

Amino acid‐based biostimulants and microbial biostimulants promote the growth, yield and resilience of strawberries in soilless glasshouse cultivation

AbstractIntroductionThe increasing demand for strawberries in the United Kingdom, valued for their flavour, nutrition and economic significance, presents challenges in maintaining consistent production, especially under various biotic and abiotic stress conditions. Traditional reliance on conventional agrochemicals to meet these demands is tempered by concerns about their health and environmental impacts, paving the way for eco‐friendly alternatives, such as biostimulants. However, their efficiency in commercial table‐top systems for June‐bearing and ever‐bearing strawberries under glasshouse conditions remains underexplored.Materials and methodsThis study investigated the efficiency of two commercial biostimulants in enhancing the growth, productivity and resilience of two strawberry varieties: ‘Malling Centenary’ (June‐bearer) and ‘Malling Ace’ (ever‐bearer) strawberry cultivars in a soilless hydroponic system within an unheated glasshouse. ‘Vitalnova Prime’ (VP), an amino acid and peptide‐based biostimulant derived from yeast, was applied every 2 weeks as a foliar spray (1 mL/L), whereas ‘Vitalnova Triboost’ (VT), a microbial inoculant with live cultures, was incorporated into the medium post‐transplanting (500 g/m3).ResultsVP significantly enhanced vegetative growth in both cultivars, resulting in substantial increases in number of leaves, crowns, crown diameter and shoot biomass accumulation compared to the control. VT also effectively improved multiple growth parameters compared to the control. Both biostimulants similarly improved crown formation and shoot dry weight in ‘Malling Centenary’. In terms of yield, both VP and VT increased yield in ‘Malling Ace’; notably, VP significantly enhanced the number of marketable fruits by 55% and average fruit weight by 56% compared to the control. Additionally, both biostimulants significantly reduced the occurrence of diseased fruits in both cultivars.ConclusionThis study demonstrates that biostimulants significantly enhance the growth, yield, and resilience of strawberries in soilless cultivation systems within unheated glasshouses. These findings suggest that biostimulants offer a sustainable and promising approach to addressing the increasing global demand for high‐quality strawberries.

Evaluation of capia pepper (C. annuum L.) inbred lines and selection of hybrid pepper varieties for protected cultivation

Pepper (Capsicum annuum L.) is one of the most produced vegetables in Turkey, both in open fields and under protected cultivation. There is a need for new hybrid varieties with various fruit types because of changing market demands. This study was carried out to determine both specific combining performances of capia pepper inbred lines and promising hybrids during two long-term production seasons in 2013 and 2014 at the Vegetable Department of Bati Akdeniz Agricultural Research Institute (BATEM). A total of 16 capia pure lines within 25 were selected by considering heterotic patterns and were crossed as 8 males and 8 females to obtain specific hybrid combinations in spring season of 2012. Sixty-four hybrids and four commercial hybrids were tested in randomized complete block design (RCBD) with two replications in 2013 in unheated glasshouse. Total fruit yield changed from 815 to 2006 g per plant. The selected 30 hybrids and 4 commercial hybrids were tested again in long-term growing season in 2014 in greenhouse and morphological characterizations of hybrids were done. Total fruit yield ranged from 1007 to 1896 g plant(-1). As a result of this study, two sweet and one hot superior capia pepper hybrids were determined as candidate for commercial market. The hybrids were also presented to private sector during growing season. The candidate capia pepper hybrid cultivars and 5 inbred lines were introduced to the private and public sector by “Products Catalogue” and some inbred lines were sold to private sector.

Cover crops and compost prevent weed seed bank buildup in herbicide-free wheat-potato rotations under conservation tillage.

Weeds are a major constraint affecting crop yields in organic farming and weed seed bank analysis can be an important tool for predicting weed infestation and assessing farming system sustainability.We compared the weed seed banks two and four years after transition from conventional to reduced tillage in organically managed winter wheat–potato cropping sequences in two replicated field trials. Experimental factors were either conventional (CT) with moldboard (25 cm) or reduced tillage (RT) with chisel ploughing (5–15 cm). Dead mulch (8–10 cm), consisting of rye–pea or triticale–vetch mixtures, was additionally applied to potatoes in the RT system. In both systems, one‐half of the plots received 5 t (ha/year) dry matter of a commercially sold yard waste compost as an organic amendment. Furthermore, subsidiary crops were grown in both systems, either as legume living mulches undersown in wheat or as cover crops sown after wheat. Prior to sowing the wheat and after potatoes, the soil seed bank from 0 to 12.5 and from 12.5 to 25 cm was sampled and assessed in an unheated glasshouse over nine months.The initial weed seed bank size in the topsoil was uniform (4,420 seedlings m−2). Two years later, wheat‐associated weeds, such as Galium aparine, Lamium spp., and Myosotis arvensis, were 61% higher on average in RT than in CT. This was independent of subsidiary crops used. In contrast, Chenopodium album, a potato‐associated weed that depends on intensive tillage, was reduced by 15% in the mulched RT system compared to CT. When RT was combined with cover crops and compost application, the seed bank did not differ significantly from the CT system.We conclude that subsidiary crops, mulches, and potentially compost are important management tools that contribute to the success of RT in herbicide‐free cereal‐based systems in temperate climates.

Conditioning the entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis megidis by pre-application storage improves efficacy against black vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) at low and moderate temperatures

Entomopathogenic nematodes (Heterorhabditis spp. and Steinernema spp.) are effective biocontrol agents for several insect pests, but their use is restricted by environmental constraints such as temperature and by their high cost. Use of nematodes against vine weevil (Otiorhynchus sulcatus) is restricted by low temperatures prevailing at the time when control is required. Here we investigate the potential for “conditioning” – storing nematode infective juveniles at 9°C for at least three weeks prior to application – to improve efficacy, both at low and moderate temperatures. Conditioned Heterorhabditis megidis were previously shown to give improved control of vine weevil when applied to potted plants at constant 9°C. Here we show similar results for Steinernema carpocapsae conditioned for 3–6weeks at 9°C. We also show that conditioning (3weeks pre-application storage at 9°C) improved efficacy of both species against vine weevil in strawberries grown in bags in an unheated glasshouse at 0–12°C. In a final experiment, we also test whether improved performance of 9°C-stored H. megidis compensates for a reduced application rate at a more permissive temperature, 15°C. Conditioned H. megidis gave control equal to that of unstored H. megidis applied at double the rate. Commercial product based on the cold-active species Steinernema kraussei was used as a reference treatment in all experiments. At constant 9°C, S. kraussei gave control superior to that of both unstored and conditioned H. megidis and S. carpocapsae, while at constant 15°C, both conditioned and unstored H. megidis applied at half the recommended rate gave superior control to S. kraussei applied at full rate. Repetition of experiments with vine weevil larvae of increasing age indicated that success of S. kraussei is more influenced by larval age than that of the other two species, and that this species is more effective against younger (2nd–3rd) than older (4th–7th) instars.

The realised and potential soil seed bank in the Potentillo albae-Quercetum community in the Białowieża Primeval Forest

Seedling emergence from soil seed bank was studied during 3 growing seasons 1997-1999 in: 1) 60 plots in 3 parts of the <em>Potentillo albae-Quercetum</em> patch: A - with <em>Carpinus betulus</em> (hornbeam) present only in the herb layer (canopy cover ca. 50-60%), B - after tree felling, at present with hornbeam dominating the shrub layer (cover > 90%), C - invaded by hornbeam 30-40 years ago (cover ca. 90%), and in 2) 60 soil samples from objects A, B, C kept in an unheated glasshouse. The results suggest that the seed bank realised in natural conditions is poorer in species with high light requirements (the Ellenberg indicator values for light (L ≥ 6) and their seedlings in comparison with the potential seed bank estimated in glasshouse conditions (field: A- 24; B - 17; C- 7, glasshouse : 44; 38; 32 species / 2 m<sup>2</sup>, field: 321; 108; 14, glasshouse: 785; 1205; 177 seedlings / m<sup>2</sup>, respectively). Contrarily, more species and seedlings with moderate light demand (L = 3-5) appeared in the field plots (field: A- 26; B- 25, glasshouse: 20; 14 species / 2 m<sup>2</sup>, field: 1014; 310, glasshouse: 328; 71 seedlings / m<sup>2</sup>). The shading by hornbeam negatively influences the size of the seed bank (field: A - 1743; B - 1226; C - 680, glasshouse: 1547; 3274; 459 seedlings / m<sup>2</sup>) and its species richness (field: A- 55; B - 48; C - 19, glasshouse: 76; 59; 56 taxa / 2 m<sup>2</sup>). Nomenclature: syntaxa - Matuszkiewicz (1981), taxa - Mirek et al. (1995).

ASSESSMENT OF GENETIC VARIABILITY OF BAMBARA GROUNDNUT (VIGNA SUBTERRANEAN (L.) VERDC.) ACCESSIONS USING MORPHOLOGICAL TRAITS AND MOLECULAR MARKERS

The efficiency of breeding can be improved by employing a number of genetic diversity measures of the crop germplasm. Genetic diversity and relatedness of 24 Bambara groundnut accessions (Vigna subterranean L. Verdc.) were estimated using 36 morphological characters, 201 Diversity Array Technology (DArT) and 65 simple sequence repeat (SSR) markers to assess the relationships between the material and also between the three marker types. These accessions were selected to represent the diversity within cultivated Bambara groundnut germplasm. A broader group of 119 Bambara groundnut accessions (87 from International Institute of Tropical Agriculture and 37 from University of Nottingham stocks; three seeds per accession) were planted in an unheated glasshouse at University of Nottingham in May, 2008. Data on the variation for morphological and agronomic traits were recorded following the IPGRI descriptors (IITA, BAMNET (2000). Samples were also analysed with microsatellite markers which have been characterised in this project. In addition, DNA extracted from the 119 accessions was sent for DArT analysis. This study has demonstrated the utility of the three marker types for genetic diversity and relatedness analysis. The genetic distance (GD) among the landraces and the first two axes for the principal component analysis (PCA) were obtained. The highest average genetic distance (GD) was obtained using morphological marker (0.55) followed by DArT (0.43) and SSR marker (0.25). The estimated values of the genetic relationship between all the markers were significantly correlated at (P<0.01). The markers provided consistent information as they produced relatively similar patterns of clustering, but DArT markers produced a cluster which grouped landraces based on their areas of origin. SSR markers have the advantage of being co-dominant and were employed to investigate pure line selection of Bambara groundnut. The results revealed significant reduction in the levels of heterogeneity from the 1st season of selection to the 3rd season, with no signs of residual heterozygosity suggesting that these lines (81-Acc-385TZA, 84-Acc 696ZMB, 88-AHM 753NAM, S19-3NAM and Bots1-BWA) have been effectively selected as pure lines. The application of SSR markers in this study further demonstrates their effectiveness as an approach suitable for Marker Assisted Selection in Bambara groundnut breeding.

Experimental study of the energy balance of unheated greenhouse under hot and arid climates: Study for the night period of winter season

In regions with warm and hot climates as is the case of several countries of the Mediterranean basin, it is interesting to study the energy balance inside a greenhouse and to quantify the heat transfers along the building components (roof, walls and ground) in winter and during night time. The present experimental work was conducted in an unheated glasshouse without crop in the region of Batna, Algeria. Three types of measurements were done from January to March: the first one is at a cloudy night; the second one at a windy night and the third one at a cloudless night. The results indicate that the greenhouse ground is considered as a significant heat source which can compensate the energy losses through the walls especially during a night preceded by a significant diurnal insulation. In addition, the convection heat transfer coefficients inside and outside the greenhouse were estimated and analysed. A good agreement with the models reported in the literature was found.

Correlation between selected parameters of planting material and strawberry yield

Abstract The aim of this study was to determine the effect of fresh and dry weight, as well as the number and length of roots and number of crowns of different types of plants, on the yield of strawberry grown for the spring and autumn harvests. Three different types of frigo strawberry plants (waiting bed plants, plug plants, A+ plants) and two strawberry cultivars (‘Honeoye’ and ‘Elsanta’) were compared in the experiment. The plants were grown in polypropylene bags in an unheated glasshouse in the years 2002-2005. The correlation coefficients were calculated to estimate the relationship of the strawberry plants’ parameters to the yield quantity. An analysis of regression for the plant parameters that most significantly correlated to the strawberry yield was carried out, which determined that the fresh and dry weight of the strawberry plants, crown number, as well as length of roots were positively correlated to the quantity of the strawberry yield. The highest positive correlation coefficient was found for the fresh weight of a whole plant and the lowest one for the number of roots.

Effect of different macrophytes in abating nitrogen from a synthetic wastewater

An experiment conducted in an unheated glasshouse from October 2006 to March 2008 studied the efficiency of different macrophytes in reducing NO 3-N and NH 4-N concentrations and loads in synthetic wastewaters. The experimental setup consisted of plastic tanks, filled with gravel and vegetated with Carex elata All., Juncus effusus L., Phragmites australis (Cav.) Trin., Typhoides arundinacea L. Moench (syn Phalaris arundinacea L.) var. picta and Typha latifolia L. There was also a control without vegetation. From January to July, a solution of 50–60 ppm of NH 4-N and NO 3-N was applied monthly; then the input concentration was doubled. The total load at the end of the experimental period was 70.4 g/m 2 of NO 3-N and 67.3 of NH 4-N. At the end of each month, water was discharged from the tanks and analysed to determine the two nitrogen forms. At the end of the experiment, 33 g/m 2 of total N (almost 24% of applied N) had disappeared in the control. Among species, the highest abatement was detected in T. latifolia (72 g/m 2, almost 52% of applied N) and the lowest in J. effusus (35%). A weekly chemical analysis in July showed that a large amount of NH 4-N quickly disappeared in all treatments, while NO 3-N only decreased in the vegetated tanks. In December, NH 4-N had similar dynamics, while NO 3-N increased. All water volumes entering and exiting the tanks were measured in order to evaluate evapotranspiration. T. latifolia showed the highest water consumption, reaching a cumulative value of above 1000 mm. At the end of the experiment, J. effusus presented the highest amount of nitrogen stored in the aerial parts (5.63 g/m 2) and T. latifolia the lowest (1.92 g/m 2).

Effect of Growth Season and Slow-Release Fertilizers on Quality Characteristics of Tomatoes

This study discusses the effect of growth season and fertilization on quality characteristics of tomatoes. In a pot experiment, established in an unheated glasshouse, tomatoes were grown in two widely differing soils during two different seasons (winter and summer). Conventional fertilizers, applied in two doses, and corresponding slow-release fertilizers, applied in a single dose, were used. Summer fruits contained greater lycopene content and had a more reddish coloration than those harvested by the end of winter. Slow-release fertilizers further increased lycopene content compared to the conventional fertilizers. The widely different electrical conductivities between the two soils had no effect on the lycopene content. Fertilization contributed to an increase of soluble solid content (Brix) in fruits, but there was no difference among fertilizers used. Similarly, there was no significant response of pulp pH to growth season or fertilizer treatments.

Effective strategy of the overwintering of semiaquatic bugs: overwintering of Velia caprai (Heteroptera: Gerromorpha: Veliidae)

Overwintering of Velia caprai was studied during the winter months 2006–2007 in the area of South Bohemia (Czech Republic) by (1) field phenological observations and samples, (2) study of artificially established experimental cohorts in an unheated glasshouse, and (3) auxiliary experiments in a laboratory. Velia caprai has a unique way of overwintering within the gerromorphan bugs that is rare among insects generally; it can overwinter in both an adult and an egg stage. Most females reach sexual maturity before overwintering, mate with mature males, overwinter actively on the water surface and lay eggs during the winter. The dormant eggs can be induced to hatch by increasing temperatures. Winter oviposition can be interpreted as a sign of a risk‐spreading reproductive strategy. The overwintering of both adults and eggs provides a chance to adapt to changes in the local environmental conditions and could be an important determinant in broad variability of life‐history traits.

Impacts of the substrate medium on tomato yield and fruit quality in soilless cultivation

The performance and suitability of different substrates for the soilless culture of tomato plants (&lt;I&gt;Lycopersicum esculentum&lt;/I&gt; Mill., cv. Belladona) were studied over a 5-month period in a closed soilless culture system employing five different substrates (perlite, pumice or maize and their mixtures with 50% shredded maize stems in an unheated glasshouse). Plants grown in a maize stem-containing medium produced earlier fruits, followed by pumice. Plants grown in pumice and perlite substrates obtained lower total yield; a higher yield was associated with the addition of maize shredded stems. Pumice + 50% maize and 100% maize produced higher total number of fruits per plant. Fruit quality parameters such as mean fruit weight, fruit firmness, total soluble solids, titratable acidity, ascorbic acid and carotenoids were influenced by the treatment, while EC, pH and dry matter content were not. The results suggest that the addition of maize in perlite and pumice could improve inorganic substrates properties for tomato soilless culture, leading to higher yields and better fruit quality.

EFFECTS OF TRICHODERMA HARZIANUM ON LETTUCE IN PROTECTEDCULTIVATION

Effects of Trichoderma harzianum on lettuce seedling development, plant quality characteristics at harvest and yield were investigated. Experiments were carried out in an unheated glasshouse where composted straw bales were used as the growing medium. A part of the experiment was carried out in a high tunnel where soil was the growing medium. Seeds were sown in peat and seedlings were grown in the presence of T. harzianum at dosages of 5, 10 and 15 g m-2 applied at sowing. Among the seedling characteristics studied only seedling fresh weight of cv. Yedikule was increased significantly. Effect of T. harzianum on lettuce yield was not statistically significant. In the glasshouse, the straw bales were composted with two different methods. In the method I, 134g N, 13g P, 25g K, and 76 g Ca, and in the method II, 54.3g N, 26g P, and 22.6g Ca were provided to the straw bales. The marketable yield of cv. Yedikule from the straw bales of method I was 503 g plant-1 from 15 g m-2 whereas the control remained the lowest with 425 g plant-1. For the same cultivar grown on the method II the highest marketable yield was obtained from 10 g m-2 with 303 g plant-1 compared to the control (150 g plant-1). The cv. Coolguard grown in the straw bales was tested only with the method I and the highest yield was from 15 g m-2 with 570 g plant-1 compared to 551 g plant-1 from the control. Dosage main effect regarding marketable yield in soil in the tunnel was not significant.

Shredded Maize Stems as an Alternative Substrate Medium

There is increased interest in the use of mixes of inorganic and organic materials as substrates in soilless culture in greenhouses, especially in parts of the world where the mixtures have not been commonly used. The potential of different ratios of shredded maize (Zea mays L.) stems as organic media on nutrient uptake, and the performance of tomato (Lycopersicon esculentum Mill.), in soilless culture, were studied. Tomato plants, cv. Belladona, were grown over a five-month period in a closed soilless culture system on four different substrates (pumice alone, shredded maize stems alone, pumice mixed with 25% or 50% maize shredded stems) and in Nutrient Film Technique, in an un-heated glasshouse. The amount of nutrient solution absorbed increased in proportion to days following transplanting, and was in part dependent on the strength of radiation and night temperature after the middle stage of growth. Plants grown on pumice + 50% maize and maize alone had similar distributions of elemental nutrient uptake. Elemental content in fruit was different only for Mn, Cu, B and Na among substrates. The ratio of number of leaves/fruit produced, favored plants grown in pumice + 50% maize, but plants grown in maize produced the greater number of fruit and the least number of leaves. No regression was observed between numbers of fruit and mean fruit weight. As nutrient uptake increased so did water uptake, with plants grown on pumice having the greater water use efficiency. The addition of maize in different ratios (25-50%) in pumice may improve its properties as a substrate for tomato soilless culture. The ratio of 50% shredded maize stems mixed with pumice could be the optimum mix for protected tomato production under the prevailing local conditions.

The effect of salt priming on the performance of differentially matured cucumber (Cucumis sativus) seeds.

The influence of salt priming (3% KNO 3 for 3 days and 1% NaCl for 2 days at 20 degree) on germination, seedling emergence and seedling dry weight of two Iranian cucumber cultivars of Basmenj and Varamin harvested at 25, 35 and 45 days after anthesis (DAA) was investigated in an unheated glasshouse. Seed germination and seedling emergence and growth were significantly affected by seed maturity and priming. Maximum advantage of priming seedling vigour was observed in seeds harvested at 25 DAA. Smaller effects of priming were also seen in the decreased mean germination and emergence times and increased seedling dry weight of seeds harvested at 35 and 45 DAA. Priming reduced percentage of seeds that germinated, but failed to emerge. In all cases, KNO 3 priming was more effective than NaCl priming. Therefore, KNO 3 priming can be used to improve cucumber seedling emergence and establishment, particularly in early spring sowings at low temperatures.

The effects of winter waterlogging and summer drought on the growth and yield of winter wheat ( Triticum aestivum L.)

Winter waterlogging and summer drought may become more prevalent as a result of climate change. Their effects on the growth and yield of winter wheat were investigated. Wheat was grown in lysimeters in an unheated glasshouse, over two seasons. Seed rate was included as an additional factor in the first season, and cultivar in the second. Root growth was investigated in both seasons using mini-rhizotrons. Waterlogging for 44 days at 93 days after sowing in 2002, and 58 days at 64 days after sowing in 2003, decreased grain yield by 20% and 24%, respectively. Drought during grain filling further decreased yields but there was no evidence that winter waterlogged plants were more susceptible to damage from drought the following summer, the effects of the two stresses being additive. Waterlogging decreased the total length, but not the final depth of the root system. Plots with a lower plant density demonstrated a smaller decrease in yield due to waterlogging. There was a significant positive linear relationship between the number of shoots per plant and nodal root axes per plant. There appeared to be a difference between cultivars in root system architecture, and in their response to waterlogging, but these differences were not reflected in grain yield.

Phytotoxicity assessment

Phytotoxicity assessment

Effect of Priming on Germination of Lagenaria siceraria Genotypes at Low Temperatures

This work was carried out to test whether germination of fifteen Lagenaria siceraria genotypes which were collected from western and southern parts of Turkey were improved by KNO3 and NaCl treatments. The experiment was conducted in two consecutive years, 2004 and 2005. Germination tests were performed at 15 0 C and 18 0 C. Results indicated that the effect of the treatments varied between the genotypes, temperatures and solutions that were used. KNO3 treatment was better and effective in larger number of lots than NaCl in both years. NaCl promoted germination in a few but inhibitive in large number of lots at both temperatures. As germination temperature was reduced, the positive effect of the KNO3 became greater. As a conclusion, priming treatments, specifically KNO3, appears to be promising in enhancing germination percentages of Lagenaria siceraria particularly at 15 0 C that is the prevailing temperature in rootstock production for grafted watermelon seedling in unheated glasshouse conditions in early spring.

Shredded Maize Stems as an Alternative Substrate Medium

Abstract The interest in the use of mixtures of inorganic and organic materials as substrate media in soilless culture in greenhouses is increasing in parts of the world where the mixtures have not been used in common practice. In this study, tomato (Lycopersicum esculentum Mill.), cv. Belladona, plants were grown over a five-month period in a closed soilless culture system on seven different substrates (perlite or pumice and their mixtures with 25% or 50% shredded maize stems) and in Nutrient Film Technique (NFT), in an unheated glasshouse. Substrate affected some characteristics of plant development and fruit yield. Plants grown on NFT were taller and had more leaves than did plants grown in perlite. Stem thickness differed according to substrate and time of measurement at 0.15, 1 and 2 m above the substrate surface. The total number of flowers and fruit produced varied with time and substrate, but there were no differences at the end of the experiment. Increased electri cal conductivity (EC) of the nutrient solution resulted in reduced numbers of flowers. The addition of shredded maize stems to mixes resulted in a higher yield, indicating there are beneficial effects of adding organic substances to inorganic substrates. Treatments did not affect occurrence of gray mold (Botrytis cinerea Pers. ex Fr.) or blossom-end rot on fruit. The results indicate that addition of shredded maize stems in perlite and pumice could improve their properties over inorganic substrates alone, and lead to improved plant development and yield for greenhouse cultured tomato.

Effect of Temperature on Expression of Gynomonoecy in Selfed-seed Populations of Spinacia oleracea L.

For an efficient harvest of self-fertilized seeds in spinach, the effect of temperature on the expression of gynomonoecy was studied by employing selfed-seed populations from three gynomonoecious plants that produced 525, 359 and 186 seeds/plant. These selfed-seed populations were named P-1, P-2, and P-3, respectively. Seeds, sown monthly from December to March in an unheated glasshouse, revealed that the frequency of gynomonoecious plants was highest in P-1 and lowest in P-3 at any sowing time. In December-sown seeds of P-1, the frequency of gynomonoecious plants was 33%; as the sowing time was delayed, the frequency of gynomonoecious plants increased until it reached 100% in the March-sown seeds. Similar results were obtained in a growth chamber kept at 15, 20 and 25°C, and under 16 h photoperiod with 120 μmol · m−2 · s−1 PPFD. However, the frequency of hermaphroditic flowers on gynomonoecious plants was affected by temperature in all three populations; it was lowest at 15°C and highest at 20°C. At 25°C, hermaphroditic flowers occurred near the shoot apex, but the number of nodes with hermaphroditic flowers was equal or less than at 20°C due to the delay in bolting and/or reduced plant height. When seedlings were transferred to 25°C after bolting was induced at 20°C for 18 days, the mean plant height was reduced but the number of nodes with hermaphroditic flowers was unaffected. This cultural manipulation seems to be advantageous for seed production because it suggests that a line with a strong expression of gynomonoecy can be selected to maximize the production of self-fertilized spinach seeds.