Tipburn Incidence Research Articles

Reduced Daily Light Integral at the End of Production Can Delay Tipburn Incidence with a Yield Penalty in Indoor Lettuce Production

Indoor vertical farms that grow lettuce commonly encounter tipburn, which is an environmental disorder caused by calcium (Ca) deficiency during the late head-forming stages of lettuce. Characterized by marginal leaf necrosis of young expanding leaves, tipburn reduces marketable yield because of the appearance of these necrotic lesions. Lowering the daily light integral (DLI) to slow the plant growth rate has been a widely practiced approach to avoid tipburn in lettuce, but it largely reduces the final yield. We assessed the effect of lowering the DLI only during the end of production, which is a critical time because it is when tipburn is typically observed. Lettuce plants of tipburn-sensitive cultivars Klee and Rex were grown under a tipburn-inducing condition in growth chambers. Sixteen days after transplanting, the DLI was varied to 100% (L100), 85% (L85), 70% (L70), or 55% (L55) of the original 17.4 mol⋅m−2⋅d−1 to grow the final 12 d. At harvest, tipburn severity was reduced by lowering the DLI, but the magnitude of reduction was cultivar-specific. For ‘Klee’, the lowest tipburn severity was found at L55 (8% ± 2.1% of leaves), but the severity was similar for all other DLI levels (33% ± 3.5% of leaves). For ‘Rex’, tipburn severity was highest in the control (L100; 14% ± 2.8% of leaves) but similar for all other DLI levels (2% ± 0.9% of leaves). Reducing the end-of-production DLI to 55% resulted in a linear decrease in yield by up to 22% and 26% for ‘Klee’ and ‘Rex’, respectively. When the increase in marketable yields and decrease in the electricity cost were considered, decreasing the end-of-production DLI yielded a profitable contribution only for ‘Klee’ (L55). For moderately tipburn-sensitive ‘Rex’, revenue losses attributable to the yield decrease were too large to justify this approach of end-of-production reduced DLI.

Effect of Soil and Foliar Application of Plant Nutrients on Purple Blotch and Tip-Burn of Onion

An experiment was conducted in the field of Plant Pathology Division, BARI, Cazipur, during Robi 2015-16, 2016-17 and 2017-18 cropping seasons to evaluate the efficacy of available plant nutrients against purple blotch disease and tip-burn of onion. Eight different plant nutrients viz. Potassium (ZnSO4 fertilizer), Phosphorus (TSP fertilizer), Boron (Boron fertilizer), Zinc (ZnSO4 fertilizer), Calcium (CaSO4 fertilizer), Copper (CuSO4), Silicon (silica gel) and Manganese (MnSO4 fertilizer) were tested against purple blotch disease and tip-burn of onion. Soil and foliar application of plant nutrients viz. Potassium, Phosphorus, Boron, Zinc, Calcium, Copper, Silicon and Manganese in the formed of water solution gave appreciable reduction of purple blotch disease and tip-burn incidence and increased plant growth such as shoot and root growth as well as yield of onion. Among the nutrients solution Potassium, Phosphorus, Silicon, Zinc and Calcium were performed better for reducing purple blotch disease severity (upto 62.78%), tip-burn incidence (upto 72.22%) and increasing plant growth as well as yield of onion. Application of Boron and Manganese also performed better than control. So, soil and foliar application plant nutrients viz. Potassium, Phosphorus, Silicon, Zinc, Boron and Manganese might be recommended for tip-burn and purple blotch disease management and also for onion production in Bangladesh. Bangladesh J. Agril. Res. 46(2): 153-165, June 2021

Exogenous brassinosteroid alleviates calcium deficiency induced tip-burn by regulating calcium transport in Brassica rapa L. ssp. pekinensis

Mini Chinese cabbage (Brassica rapa L. ssp. Pekinensis) plays an important role in the supply of summer vegetables on the plateau in western China. In recent years, tip-burn has seriously affected the yield, quality and commodity value of mini Chinese cabbage. Calcium (Ca2+) deficiency is a key inducer of tip-burn. As a new type plant hormone, brassinolide (BR) is involved in regulating a variety of biotic and abiotic stresses. To explore the alleviation role of BR in tip-burn caused by Ca2+ deficiency, a hydroponic experiment was conducted to study the relationship between BR and Ca2+ absorption and transport. The results showed that foliar spraying with 0.5 µM BR significantly reduced tip-burn incidence rate and disease index of mini Chinese cabbage caused by Ca2+ deficiency. Moreover, the dynamic monitoring results of tip-burn incidence rate showed that the value reached the highest on the ninth day after treatment. BR promoted the Ca2+ transport from roots to shoots and from outer leaves to inner leaves by increasing the activities of Ca2+-ATPase and H+-ATPase as well as the total ATP content, which provided power for Ca2+ transport. In addition, exogenous BR upregulated the relative expression levels of BrACA4, BrACA11, BrECA1, BrECA3, BrECA4, BrCAX1, BrCAS and BrCRT2, whereas Ca2+ deficiency induced down-regulation. In conclusion, exogenous BR can alleviate the Ca2+-deficiency induced tip-burn of mini Chinese cabbage by promoting the transport and distribution of Ca2+.

Influence of Day and Night Temperature and Radiation Intensity on Growth, Quality, and Economics of Indoor Green Butterhead and Red Oakleaf Lettuce Production

Lettuce (Lactuca sativa) is among the most consumed vegetables worldwide and is primarily field-grown; however, indoor agriculture enables year-round, precise production. Through precise manipulation of the mean daily temperature (MDT) and photosynthetic photon flux density (PPFD), crop color, morphology, and yield can be altered. Therefore, we quantified how MDT and PPFD interact and developed models predicting yield and economic viability. Eleven days after sowing, green butterhead lettuce ‘Rex’ and red oakleaf lettuce ‘Rouxaï RZ’ were transplanted into six deep-flow hydroponic tanks with day/night and MDTs of 22/15 °C (20 °C), 25/18 °C (23 °C), or 28/21 °C (26 °C), under light-emitting diodes providing a low or high PPFD of 150 or 300 µmol·m−2·s−1 for 17-h·d−1. As PPFD increased, shoot fresh mass (SFM) of ‘Rex’ increased by 29% (33.4 g). SFM of ‘Rouxaï RZ’ and shoot dry mass (SDM) of both cultivars was influenced by the interaction of MDT and PPFD. The greatest ‘Rouxaï RZ’ SFM (158.8 g) and SDM (6.42 g) were recorded at >20 °C MDT under the high PPFD; the lowest SFM (76.0 g) and SDM (3.17 g) occurred at 20 °C under the low PPFD. Similarly, ‘Rex’ SDM was greatest (7.36 g) and lowest (3.78 g) under the aforementioned MDTs and PPFDs. Increasing from the low to high PPFD increased tipburn incidence on ‘Rouxaï RZ’ from 0 to 25% and ‘Rex’ from 47 to 100%. ‘Rouxaï RZ’ had darker yellow-red foliage at lower MDTs under the high PPFD. A high MDT and low PPFD resulted in a lighter green. Finally, for the greatest SFM, while reducing energy costs as interpreted from the economic analysis, we recommend growing ‘Rex’ and ‘Rouxaï RZ’ under a PPFD of 150 and 300 µmol·m−2·s−1, respectively, at an MDT of 23 to 26 °C depending on the cost of temperature control.

Exogenous brassinosteroids alleviate calcium deficiency-induced tip-burn by maintaining cell wall structural stability and higher photosynthesis in mini Chinese Cabbage.

Tip-burn has seriously affected the yield, quality and commodity value of mini Chinese cabbage. Calcium (Ca2+) deficiency is the main cause of tip-burn. In order to investigate whether exogenous brassinosteroids (BRs) can alleviate tip-burn induced by calcium (Ca2+) deficiency and its mechanism, in this study, Ca2+ deficiency in nutrient solution was used to induced tip-burn, and then distilled water and BRs were sprayed on leaves to observe the tip-burn incidence of mini Chinese cabbage. The tip-burn incidence and disease index, leaf area, fluorescence parameters (Fv/Fm, NPQ, qP andφPSII) and gas exchange parameters (Tr, Pn, Gs and Ci), pigment contents, cell wall components, mesophyll cell ultrastructure and the expression of genes related to chlorophyll degradation were measured. The results showed that exogenous BRs reduced the tip-burn incidence rate and disease index of mini Chinese cabbage, and the tip-burn incidence rate reached the highest on the ninth day after treatment. Exogenous BRs increased the contents of cellulose, hemifiber, water-soluble pectin in Ca2+ deficiency treated leaves, maintaining the stability of cell wall structure. In addition, BRs increased photosynthetic rate by increasing the activities of Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and fructose 1,6-bisphosphatase (FBPase) related to Calvin cycle, maintaining relatively complete chloroplast structure and higher chlorophyll content via down-regulating the expression of BrPPH1 and BrPAO1 genes related to chlorophyll degradation. In conclusion, exogenous BRs alleviated calcium deficiency-induced tip-burn by maintaining cell wall structural stability and higher photosynthesis.

Influence of calcium macronutrient on tip burn occurrence in hydroponically cultivated lettuces

Tip burn in hydroponics lettuce is an undesirable phenomenon identified by necrotic breakdown of marginal tissue of leaves. A deep-water culture hydroponics system was designed to determine the effect of increasing nutritional calcium concentration and varying nutritional calcium sources in alleviating the tip burn development for the hydroponics growth of lettuce (Lactuca sativa). Lettuces was cultivated separately in an untreated fish wastewater (150mg/L) and four treated fish wastewaters with calcium addition by calcium hydroxide and calcium carbonate to concentrations of 250 and 350mg/L respectively. Increasing calcium concentration from 150 to 350mg/L demonstrated not only an increase in tip burn incidence by 33.33% (calcium carbonate) and 50% (calcium hydroxide), but a slower plant growth in comparison with lettuces cultivated at 150mg/L. Besides, lettuces treated by calcium carbonate has greater leaf calcium concentrations by 48.17% at constant calcium concentration, attributed to its high solubility to release more Ca2+ ions in fish wastewater for plant adsorption. Results suggest that the addition of calcium carbonate to fish wastewater for hydroponics cultivation is more suitable for reducing the tip burn occurrence and growth inhibition at concentrations up to 150mg/L.

Effect of Soil and Foliar Application of Plant Nutrients on Purple Blotch and Tip-Burn of Garlic

An experiment was conducted in the field of Plant Pathology Division, BARI, Joydebpur to evaluate the efficacy of available plant nutrient for the development of purple blotch disease and tip-burn of onion. Eight different treatments viz. Potassium (MP fertilizer), Phosphorus (TSP fertilizer), Boron (Boron fertilizer), Zinc (ZnSO4 fertilizer), Calcium (CaSO4 fertilizer), Copper (CuSO4), Silicon (silica gel) and Manganese (MnSO4 fertilizer) were tested against purple blotch disease and tip-burn of garlic. The present study revealed that soil and foliar application of plant nutrients viz. Potassium, Phosphorus, Boron, Zinc, Calcium, Copper, Silicon and Manganese gave appreciable reduction of purple blotch disease and tip-burn incidence and increased plant growth parameters such as shoot and root growth as well as yield of garlic. Among the nutrients Potassium, Phosphorus, Silicon, Zinc and Calcium were performed better for reducing purple blotch disease severity, tip-burn disease incidence and increasing plant growth as well as yield of garlic. Application of Boron and Manganese also performed better than control. So, soil and foliar application plant nutrients Potassium, Phosphorus, Silicon, Zinc, Boron and Manganese may be recommended for tip-burn and purple blotch disease management and for garlic production in Bangladesh.

Effects of Magnesium Application on Tipburn Incidence and Calcium Acquisition in Lisianthus (Eustoma grandiflorum) Cultivars

The occurrence of tipburn is a severe problem in horticulture crop production. A previous study suggested that, in lisianthus, tipburn is caused by imbalanced calcium (Ca) distribution. However, there are few studies on the effects of other cations on tipburn incidence in lisianthus cultivars. In this study, to determine the effect of Magnesium (Mg) concentration in nutrient solution on tipburn incidence and Ca and Mg acquisition, three lisianthus cultivars (‘Celeb Wine’: CW, ‘Reina White’: RW, and ‘Voyage Peach’: VP) were cultivated under different Mg concentrations in nutrient solution (12 ppm, 34.7 ppm, and 75.4 ppm). Under high nutritional Mg concentrations, CW and RW had significantly decreased tipburn severity, while VP showed no significant differences in tipburn severity among the treatments. Total Ca concentrations in all cultivars significantly increased at higher nutritional Mg concentrations, which indicated that Mg application in lisianthus cultivars promoted Ca acquisition. Furthermore, it was suggested that CW and RW had the ability to distribute increased Mg to the tip of the upper leaves, thereby promoting Ca distribution. Thus, a decrease in tipburn severity in CW and RW at higher nutritional Mg concentrations appeared to occur.

Effects of Temperature Variations during Light Period on Growth and Tipburn Incidence of Hydroponic Leaf Lettuce Grown under Artificial Lighting

Effects of Temperature Variations during Light Period on Growth and Tipburn Incidence of Hydroponic Leaf Lettuce Grown under Artificial Lighting

High-resolution genetic dissection of the major QTL for tipburn resistance in lettuce, Lactuca sativa.

Tipburn is an important physiological disorder of lettuce, Lactuca sativa L., related to calcium deficiency that can result in leaf necrosis and unmarketable crops. The major quantitative trait locus (QTL), qTPB5.2, can account for up to 70% of the phenotypic variance for tipburn incidence in the field. This QTL was genetically dissected to identify candidate genes for tipburn by creating lines with recombination events within the QTL and assessing their resistance to tipburn. By comparing lines with contrasting haplotypes, the genetic region was narrowed down to ∼877 Kb that was associated with a reduction of tipburn by ∼60%. Analysis of the lettuce reference genome sequence revealed 12 genes in this region, one of which is a calcium transporter with a single nucleotide polymorphism in an exon between haplotypes with contrasting phenotypes. RNA-seq analysis of recombinants revealed two genes that were differentially expressed between contrasting haplotypes consistent with the tipburn phenotype. One encodes a Teosinte branched1/Cycloidea/Proliferating Cell factor transcription factor; however, differential expression of the calcium transporter was detected. The phenotypic data indicated that there is a second region outside of the ∼877 Kb region but within the QTL, at which a haplotype from the susceptible parent decreased tipburn by 10–20%. A recombinant line was identified with beneficial haplotypes in each region from both parents that showed greater tipburn resistance than the resistant parent; this line could be used as the foundation for breeding cultivars with more resistance than is currently available.

Genotype-Dependent Tipburn Severity during Lettuce Hydroponic Culture Is Associated with Altered Nutrient Leaf Content

Cultivated lettuce (Lactuca sativa L.) is one of the most important leafy vegetables in the world, and most of the production is concentrated in the Mediterranean Basin. Hydroponics has been successfully utilized for lettuce cultivation, which could contribute to the diversification of production methods and the reduction of water consumption and excessive fertilization. We devised a low-cost procedure for closed hydroponic cultivation and easy phenotyping of root and shoot attributes of lettuce. We studied 12 lettuce genotypes of the crisphead and oak-leaf subtypes, which differed on their tipburn resistance, for three growing seasons (Fall, Winter, and Spring). We found interesting genotype × environment (G × E) interactions for some of the studied traits during early growth. By analyzing tipburn incidence and leaf nutrient content, we were able to identify a number of nutrient traits that were highly correlated with cultivar- and genotype-dependent tipburn. Our experimental setup will allow evaluating different lettuce genotypes in defined nutrient solutions to select for tipburn-tolerant and highly productive genotypes that are suitable for hydroponics.

Excessive Calcium Accumulation in the Roots Is a Key Factor in Tipburn Incidence under High Ca Supply in Lisianthus (Eustoma grandiflorum) Cultivars

In lisianthus cultivars, the occurrence of tipburn is known to adversely affect quality and yield. However, information concerning the responses of tipburn incidence to different levels of Ca is limited. In addition, only a few studies have investigated the effect of potassium (K) concentration on Ca acquisition and distribution in lisianthus. To address this knowledge gap, we investigated tipburn incidence in three lisianthus cultivars (Umi honoka (UH), Reina white (RW), and Voyage peach (VP)) and the Ca and K concentrations in them under different concentrations of Ca supply (40, 80, and 120 ppm). These cultivars exhibited different responses to different concentrations of Ca supply. Tipburn was not observed in UH. In RW, tipburn incidence and severity significantly decreased with an increase in nutritional Ca concentration, because the Ca concentration in the tips of the top leaves significantly increased with Ca concentration. By contrast, in VP, tipburn incidence under all treatments was 100%, and there was no significant difference in the Ca concentration in the tips of the top leaves among the treatments, but the total Ca concentration significantly increased. VP was the only cultivar that significantly acquired and accumulated more Ca in the roots with an increase in nutritional Ca concentration. Overall, excessive Ca accumulation in the roots under high-Ca conditions inhibits the distribution of Ca to the tips of the top leaves and eventually manifests as tipburn in the cultivar. In addition, our results suggested that the content ratio of K in the nutrient solutions did not prevent Ca acquisition and distribution in lisianthus cultivars and that the K concentration has a negligible effect on the occurrence of tipburn.

Effect of Cropping System and Humidity Level on Nitrate Content and Tipburn Incidence in Endive

Tipburn is an important disorder caused by a calcium deficiency that affects the marketability of endives. Genotype, air relative humidity, and temperature are directly involved in tipburn occurrence. Our study aimed to investigate the effect of cropping systems and relative humidity on the marketable yield, nitrate accumulation, and incidence of tipburn in endives. Two cultivars were evaluated in pots (‘Cuartana’ and ‘Natacha’), two cropping systems (greenhouse and open-field), and in two different air humidity levels (high level: plants under a plastic tunnel with an extra supply of humidity with micro-sprinklers, and low level: plants without an extra supply of humidity and outside of a plastic tunnel) during two years (2013 and 2014) in different growing seasons. Nitrate content was determined by reflectometry, and tipburn was evaluated using a qualitative scale. Results showed that tipburn was favored under greenhouse with low humidity levels, with 40–60% plants affected. ‘Natacha’ was more susceptible to tipburn (>20% plants affected) than ‘Cuartana’ (<20% plants affected). Leaf nitrate accumulation was favored by the highest temperatures (greenhouse). It is concluded that in our conditions, tipburn incidence in endives depends on the interaction of genotype and the environmental conditions. Nitrate content was more influenced by the temperature than by the cultivars used.

Tipburn Incidence and Ca Acquisition and Distribution in Lisianthus (Eustoma grandiflorum (Raf.) Shinn.) Cultivars under Different Ca Concentrations in Nutrient Solution

Tipburn (calcium (Ca) deficiency disorder) is a major problem in the production of lisianthus cultivars. However, few studies have investigated the influence of different Ca concentrations in nutrient solution on tipburn incidence and Ca acquisition and distribution. Thus, it remains unclear why some cultivars exhibit tipburn under high Ca concentrations. To address this, we used three lisianthus cultivars ‘Azuma-no-Kaori’ (AK), ‘Celeb Wine’ (CW), and ‘Voyage Yellow’ (VY) and compared tipburn incidence and Ca acquisition and distribution under different Ca concentrations in a nutrient solution (low (40 ppm), moderate (80 ppm), and high (120 ppm) Ca). Tipburn severity and incidence in AK and VY significantly decreased with increasing nutritional Ca concentrations; the Ca concentrations in each organ and Ca acquisition competence (RGRCa) increased at higher nutritional Ca concentrations. In contrast, tipburn incidence in CW was 100% for all treatments. In CW, Ca acquisition competence and Ca concentrations in most organs increased with increasing nutritional Ca concentrations, but the Ca concentrations in the tips of the upper leaves did not differ significantly between treatments. Thus, our results suggest that the cause of tipburn under sufficient Ca conditions is an inability of the plant to distribute Ca to the tips of its upper leaves.

Quality, Yield, and Biomass Efficacy of Several Hydroponic Lettuce (Lactuca sativa L.) Cultivars in Response to High Pressure Sodium Lights or Light Emitting Diodes for Greenhouse Supplemental Lighting

Lettuce is an economically important crop that can be grown either in the field or greenhouse. Different challenges are present in either environment; therefore, cultivar selection is important. For hydroponic greenhouse lettuce there is relatively little published information on cultivar selection under different lighting sources. The objective of phase 1 was to determine the influence of lighting using high pressure sodium (HPS) or light emitting diodes (LED) on plant fresh weight, height, tip burn index, bolting, and Brix. Phase 2 was similar to phase 1 but with fewer cultivars (1) to allow for greater number of replicates per treatment per crop cycle. Each experiment consisted of three crop cycles over time per phase. Light sources were controlled using an algorithm, Light and Shade System Implementation (LASSI), to achieve a constant average daily light integral under each treatment and crop cycle. Electrical consumption and efficacy (fresh weight per kWh) from each treatment was estimated using data collected on power consumption from representative lamps multiplied by the number of fixtures and the hours fixtures were on per crop cycle. In phase 1, the fresh weight of 2 to 3 cultivars was greater under HPS and 1 to 2 cultivars under LED, depending on production cycle. The HPS-grown lettuce tended to have more tip burn and bolting in crop cycles 1 and 2, with cycle 3 showing similar tip burn incidence. Bolting was only consistently observed in one cultivar, ‘Teodore’. The LED array used less than half as much electricity as the HPS array, while producing relatively similar size lettuce, therefore, leading to electrical efficacies two- to three-times higher in LED than in HPS treatments. In phase 2, significant differences in height were found in ‘Greenstar’ and ‘Xandra’, with HPS producing larger plants than LED. Significant differences were also found in diameter in ‘Greenstar’, ‘Xandra’, ‘Locarno’, and ‘Crunchita’, with HPS again being larger than LED.

Genetic architecture of tipburn resistance in lettuce.

Two major QTLs for tipburn were identified in LGs 1 and 5 contributing to resistance in cv. Salinas. The findings suggest pleiotropic effects between leaf crinkliness/savoy and tipburn. Tipburn is a physiological disorder in lettuce that is thought to be caused by a localized deficiency of calcium in leaf tissues. To elucidate the genetic architecture of resistance to tipburn in lettuce, seven recombinant inbred line populations were analyzed in multiple environments and years to identify quantitative trait loci (QTLs) for tipburn. Core height, head firmness, head closure, leaf crinkliness, plant fresh weight, and leaf savoy were also analyzed to investigate whether QTLs for these morphological traits collocated with QTLs for tipburn, which would be indicative of pleiotropic effects. Twenty-three major, intermediate, and minor unique QTLs for tipburn were identified in one or more populations scattered throughout the genome. Two major QTLs for tipburn incidence were identified in linkage groups (LGs) 1 and 5, which determined up to 45 and 66% of the phenotypic variance. The major QTL in LG 1 collocated with the head firmness QTL. The major QTL in LG 5 collocated with the QTL for core height, leaf crinkliness, and head firmness. Further research is needed to determine whether these associations are due to pleiotropic effects of the same gene or if the genes determining these traits are tightly linked. The beneficial alleles at the QTLs in LGs 1 and 5 are present in Lactuca sativa cv. Salinas, the genotype sequenced for the reference genome assembly. Therefore, these QTLs are good targets to identify genes causing tipburn as well as regions for marker-assisted selection to improve resistance to tipburn in lettuce.

EFFECT OF DIFFERENT K+/CA2+ RATIOS ON YIELD, QUALITY AND PHYSIOLOGICAL DISORDER IN SOILLESS STRAWBERRY CULTIVATION

The balance of mineral nutrients in plant nutrient solutions has an influence on yield, fruit quality and physiological disorder of strawberries grown in soilless conditions. Nutrient solutions that enhance the yield and quality of plants grown in soilless conditions are optimized through anion-cation equilibrium, optimum K++Ca2+/Mg2+ and K+/Ca2+ ratios. In this study, the effect of three different K+/Ca2+ ratios (5.5/7.0; 5.0/7.0; 6.0/6.0) on some morpho-physiological features (crown diameter, chlorophyll index, leaf temperature), fruit yield, fruit quality (fruit weight, total soluble solids, titratable acidity, ascorbic acid, firmness) and physiological disorder (tip burn) of ‘Albion’ and ‘Festival’ strawberries, were investigated. Results show that increasing K+/Ca2+ ratios significantly accelerated the tip burn incidence. On the other hand, the highest yield, firmness and the lowest tip burn were achieved at 5.5/7.0 ratio of K+/Ca2+ treatment.

Optimization of temperature and light, and cultivar selection for the production of high-quality head lettuce in a closed-type plant factory

Two separate experiments were conducted to identify suitable cultivars, to optimize light and temperature, and to understand the heading process in order to produce high-quality crisphead lettuce (Lactuca sativa L.) in a closed production environment. Three commercial crisphead lettuce cultivars (‘Adam’, ‘Manchu’, and ‘Sensation’) were grown on deep flow technique beds in a closed-type plant factory under three different fluorescent light intensities [150, 200, and 250 µmol m−2 s−1 photosynthetic photon flux (PPF)] and two temperature conditions. The plants were grown until 60 days after transplantation (DAT) under the high [22/18 °C (0–30 DAT) → 18/16 °C (30–60 DAT)] and low [18/16 °C (0–30 DAT) → 18/14 °C (30–60 DAT)] temperature conditions, with 50 ± 10% relative humidity and a 12-h day length. Growth parameters, including head formation rate and tip burn incidence, were measured in all experiments. All cultivars exhibited significantly higher growth rates in the 250 µmol m−2 s−1 light intensity compared to lower light intensities under both temperature conditions, and showed a cultivar-specific difference in the growth pattern at different light intensities. Our cultivation trials suggest that ‘Sensation’ is ideal for production in closed-type plant factory systems at 250 µmol m−2 s−1 PPF due to its stable head formation and superior head quality. Under the high temperature condition, head formation was only observed in two cultivars, ‘Sensation’ and ‘Adam’, while all cultivars showed head formation in the low temperature condition. The initiation of head formation began at the 8–10 true-leaf stage around 20 DAT, and then apparent head formation was observed around 30 DAT, followed by an increase of head density until harvest (60 DAT). Tip burn symptoms were observed throughout the experiment, with higher values in the high temperature condition. The results of our study suggest that good head formation can be achieved under high light intensities ( ≥ 200 µmol m−2 s−1 PPF) and low temperature [18/16 °C (0–30 DAT) → 18/14 °C (30–60 DAT)] in crisphead lettuce grown in a closed-type plant factory.

Shade cloths and polyethylene covers have opposite effects on tipburn development in greenhouse grown lettuce

Spring-summer production of lettuce under greenhouses is highly affected by Tipburn development, a physiological disorder attributed to localized calcium (Ca) deficiency. As Ca is distributed along the plant tissues together with the water flux, Tipburn development is related to environmental conditions. Until now, no growing condition that avoids this disorder, without an associated yield penalty, has been clearly identified. In this work we used shade cloth (SC) or polyethylene (PE) covers in a greenhouse to modify the growing environment of pot-grown lettuce and to examine the effect of these conditions on growth and Tipburn severity. Two levels of Ca in the soil were evaluated. PE generated a good environment for lettuce growth reflected in high dry mass. However, high Tipburn development occurred despite Ca concentration being higher than in leaves of control lettuces. SC generated a similar environment to control conditions but with a lower light intensity. Under this environment dry mass production was lower than in control plants and plants produced thin and elongated leaves. Under SC no Tipburn symptoms were registered irrespective of soil Ca level and leaf Ca content was higher than in control plants. Ca fertilization had no effect on Tipburn development in either of these treatments. These results reinforce the idea that Tipburn is a physiological disorder related to environmental conditions rather than Ca deficiencies. Results highlight that 1- the use of Polyethylene as SC increased Ca content in lettuce leaves in respect to control plants but both treatments had opposite Tipburn incidence; 2- SC significantly reduced dry weight of plants and improved Ca distribution towards leaf margins; and, 3- Ca fertilization had no effect on Tipburn development in any of the treatments. Overall these results reinforce the idea that Tipburn is a physiological disorder related to environmental conditions.

Relevance of tipburn incidence to the competence for Ca acquirement and Ca distributivity in lisianthus [Eustoma grandiflorum (Raf.) Shinn.] cultivars

Tipburn is a severe problem that can occur during the propagation of several lisianthus [Eustoma grandiflorum (Raf.) Shinn.] cultivars. However, its incidence has not yet been established. Moreover, few studies have addressed the association between calcium (Ca) acquirement competence and the occurrence tipburn. The present study compared tipburn incidence and severity, plant growth rate, Ca acquirement competence (RGRCa), and Ca distributivity in 14 lisianthus cultivars. The influence of these traits on the occurrence of tipburn has also been discussed. To quantify Ca acquirement competence for each cultivar, plant growth and Ca content were analyzed together. It was determined that there were significant differences among lisianthus cultivars in terms of tipburn severity and incidence. However, these differences were not significantly correlated with either plant growth rate or Ca acquirement competence. In contrast, the parameters related to Ca distributivity to the upper leaf tips were significantly correlated with tipburn severity and incidence. Therefore, it became clear that the occurrence of tipburn in lisianthus cultivars is caused mainly by the inability of the plant to translocate adequate amounts of Ca to the tips of the upper leaves. Ca acquirement competence (RGRCa) were not significantly associated with tipburn severity and incidence in lisianthus cultivars. Nevertheless, growth analysis based on plant Ca content quantified Ca acquirement competence (RGRCa) and established the relevance of physiological (SARCa) and morphological traits (RMR and lCa−1) and RGRCa. This analytical method is a new approach towards understanding the nutrient economy of a plant at risk of deficiency.