Effects of calcium and magnesium on growth, fruit yield and quality in a fall greenhouse tomato crop grown on rockwool

Transcription

1 Effects of calcium and magnesium on growth, fruit yield and quality in a fall greenhouse tomato crop grown on rockwool Xiuming Hao and Athanasios P. Papadopoulos Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Research Centre, Harrow, Ontario, Canada N0R 1G0 ( haox@agr.gc.ca) Received 24 September 2002, accepted 22 May Hao, X. and Papadopoulos, A.P Effects of calcium and magnesium on growth, fruit yield and quality in a fall greenhouse tomato crop grown on rockwool. Can. J. Plant Sci. 83: Tomato (Lycopersicon esculentum Mill.) Trust was grown on rockwool with two concentrations of calcium (150 and 300 mg L 1 ) in combination with four concentrations of magnesium (20, 50, 80 and 110 mg L 1 ) in fall, 1999, to investigate their effects on plant growth, leaf photosynthesis, and fruit yield and quality (fruit firmness, dry matter, soluble solids and russeting). High Ca (300 mg L 1 ) concentration increased fruit yield and reduced the incidence of blossom-end rot (BER) and fruit russeting, compared with the low Ca concentration (150 mg L 1 ). High Ca concentration reduced fruit firmness but did not affect fruit size and leaf photosynthesis. Plants grown at 20 mg L 1 Mg started to show leaf chlorosis on both the middle and bottom leaves 8 wk after planting. Leaves with moderate chlorosis lost about 50% of their photosynthetic capacity. Fruit yield in the late growth stage decreased at 20 mg L 1 Mg. Blossom-end rot incidence increased linearly with increasing Mg concentration in the early growth stage at low Ca, but BER incidence at high Ca was not affected by Mg concentration. Fruit firmness increased with increasing Mg concentration at low Ca. At high Ca, Mg concentration affected fruit firmness only late in the season; fruit firmness at 80 mg L 1 Mg was higher than at 50 mg L 1 Mg concentration. Fruit russeting in mid-season was affected by nutrient treatments, being the least at 300/50 mg L 1 Ca/Mg. Therefore, for a fall greenhouse tomato crop, the optimum Ca/Mg concentration for tomato production is estimated to be 300/50-80 mg L 1. The Mg concentration may be started at 50 mg L 1 and gradually increased to 80 mg L 1 towards the end of the season, to improve plant growth and fruit firmness. Key words: Greenhouse, tomato, Lycopersicon esculentum, yield, quality, photosynthesis, calcium, magnesium Hao, X. et Papadopoulos, A. P Effets du calcium et du magnésium sur la croissance, le rendement et la qualité des fruits de tomate d automne cultivée en serre dans de la laine minérale. Can. J. Plant Sci. 83: À l automne 1999, les auteurs ont cultivé la tomate (Lycopersicon esculentum Mill.) Trust dans de la laine minérale à deux concentrations de calcium (150 et 300 mg par L) et quatre de magnésium (20, 50, 80 et 110 mg par L) afin de vérifier l effet de ces deux éléments sur la croissance, la photosynthèse dans les feuilles ainsi que le rendement fruitier et la qualité des fruits (fermeté, matière sèche, solides hydrosolubles et roussissement). Une forte concentration de Ca (300 mg par litre) améliore le rendement fruitier et diminue l incidence de la nécrose apicale et du roussissement, comparativement à une concentration plus faible (150 mg par litre). Une plus grande concentration de Ca attendrit les fruits, mais n en change pas le calibre et n agit pas sur la photosynthèse. Les feuilles des plantes recevant 20 mg de Mg par litre commencent à présenter des signes de chlorose au bas et au milieu du plant huit semaines après la mise en terre. Les feuilles modérément attaquées par la chlorose perdent environ la moitié de leur pouvoir de photosynthèse. À 20 mg de Mg par litre, le rendement fruitier diminue à la fin de la période de croissance. L incidence de la nécrose apicale progresse de façon linéaire avec la concentration de Mg au début de la croissance, à faible concentration de Ca, mais elle n est pas affectée si l apport de Ca est plus grand. Le fruit devient plus ferme quand la concentration de Mg augmente, à faible dose de Ca. Quand la concentration de Ca est élevée, la concentration de Mg n affecte la fermeté des fruits qu en fin de saison; les fruits sont plus fermes avec 80 mg qu avec 50 mg de Mg par litre. Les éléments nutritifs affectent le roussissement en milieu de saison, cette condition étant la plus bénigne avec la combinaison 300/50 mg Ca/Mg par litre. Pour cultiver des tomates en serre à l automne, la concentration optimale de Ca/Mg devrait donc être de 300/50 à 80 mg par litre. On pourrait commencer avec 50 mg de Mg par litre et augmenter graduellement la dose à 80 mg en fin de la saison pour améliorer la croissance des plants et la fermeté des fruits. Mots clés: Serre, tomate, Lycopersicon esculentum, rendement, qualité, photosynthèse, calcium, magnésium Greenhouse tomato is the most important vegetable crop in Canada; its production has substantially increased in the past few years. The farm gate value in Ontario alone reached $217 million in 2002 (S. Khosla, OMAF, personal communication). Almost all the greenhouse tomatoes in Canada are produced with soilless culture systems, mostly on rockwool. Rockwool releases little or no plant nutrients and therefore almost all the nutrients required by the plants need to be supplied continuously by the grower. 903 Calcium is one of the most important mineral nutrients in greenhouse tomato production. Calcium deficiency in tomato reduces leaf size, and causes necrosis of young leaves and yield loss in extreme cases (Adams and el-gizawy 1988; Holder and Cockshull 1990; Adams and Holder 1992). A Abbreviations: BER, blossom-end rot; CF, catfaced; EC, electrical conductivity; MF, maximum force for fruit pericarp tissue failure; SLOPE, slope of the force vs. displacement curve in the linear phase of fruit firmness test

2 904 CANADIAN JOURNAL OF PLANT SCIENCE low supply of calcium to fruit leads to increased tomato fruit cracking (Simon 1978) and blossom-end rot (BER; Ho et al. 1999). Excessive supply of calcium to fruit causes goldspecks/goldspots, cells containing calcium oxalate crystals (Den Outer and van Veenendaal 1988; De Kreij et al. 1992; Ho et al. 1999), which not only affects the appearance of the fruit, but also reduces its shelf life (Janse 1988). Calcium foliar spray increased the firmness of tomato fruit measured with and without the skin present (Garcia et al. 1995). Although Ca salts have widely been used in the tomato processing industry to improve tomato tissue integrity and firmness, very few studies have been conducted on the effects of Ca concentration in the nutrient solution on fresh market tomato texture, and the results are far from conclusive (Barrett et al. 1998). There is limited information available on the effects of Ca on fruit russeting, fine hair-like cuticle cracks, which has become a major quality problem in summer greenhouse tomato production in Canada and elsewhere (Dorais et al. 2001). Magnesium deficiency often occurs in greenhouse tomatoes. However, it hardly ever attracts any attention because the deficiency symptoms usually occur on the oldest leaves, which are generally thought to have little or minor impact on productivity. In a fall tomato crop grown on rockwool, the deficiency occurs on the middle leaves, which indicates that Mg deficiency could have significant influence on fall greenhouse tomato productivity (Sonneveld and Voogt 1991). The antagonism between Ca and Mg is well known; the rate of Mg uptake can be depressed by Ca and vice versa (Sonneveld 1987; Ho and Adams 1995; Paiva et al. 1998). Despite its antagonistic relationship with Ca, and despite the many studies on the effects of Ca on fruit quality, little has been done to investigate the effects of Mg on greenhouse tomato fruit quality. The uptake and optimum levels of Ca and Mg for greenhouse tomatoes are strongly affected by climatic conditions such as solar irradiance, humidity and temperature (Sonneveld 1987; Sonneveld and Voogt 1991; Adams 1994; Ho et al. 1999; Papadopoulos and Hao 2002). Ontario, especially the Leamington area (41 N, continental climatic type; largest greenhouse tomato production area in North America), has quite different climatic conditions from the major greenhouse vegetable production areas in northern Europe (close to 50 N; maritime climatic type). To date, most of the information available on the effects of Ca and Mg was generated from research conducted in northern Europe. This study was undertaken to investigate the effects of Ca, Mg, and their interactions on plant growth, photosynthesis, fruit yield and quality for optimizing the mineral nutrition of greenhouse tomato under continental climatic conditions. MATERIALS AND METHODS A fall experiment was conducted in a large glasshouse (200 m 2 ) from August to December 1999, at the Greenhouse and Processing Crops Research Centre (GPCRC), Agriculture and Agri-Food Canada, Harrow (41 N), Ontario, Canada. Tomato (cv. Trust) seed was sown in small rockwool cubes ( cm 3, Fibrex Insulation Inc., Sarnia, ON, Canada) in seedling packs on 28 June. After seedlings emerged and cotyledons became fully unfolded, the seedlings were transplanted into large rockwool blocks ( cm 3, Fibrex Insulation Inc., Sarnia, ON, Canada). The transplants were raised on benches and flood irrigated using a Harrow Fertigation Manager (Papadopoulos and Liburdi 1989) according to standard nutrient recommendations (Papadopoulos 1991). On 30 July 1999, at the four- to five-leaf stage, transplants were transferred onto sleeved rockwool slabs ( cm 3, Fibrex Insulation Inc., Sarnia, ON, Canada) in the glasshouse, at 2.7 plants m -2 density. Day/night heating temperature was set at 19/18 C while ventilation temperature was set at 23 C. Relative humidity (RH) was maintained between 65 and 85%. Plants were trained to a single stem according to commercial practices. An electrical vibrator was used to assist flower pollination daily. The plants were drip-irrigated with appropriate nutrient solutions in an open rockwool production system; to avoid nutrient imbalances in the rockwool slabs, 20 30% extra nutrient solution was applied (Papadopoulos 1991). The glasshouse was equipped with a thermal curtain which was closed during the nighttime in November and December. The light transmission of the glasshouse was, on the average, at about 70%. Nutrient Treatments Eight nutrient treatments were applied: factorial combinations of two Ca concentrations (150 and 300 mg L 1 ) and four Mg concentrations (20, 50, 80 and 110 mg L 1 ). The treatments were arranged in four randomized complete blocks, each plot made up of 12 plants. There was a total of 48 plants in each treatment. Data were collected on the middle 10 plants in each plot. Appropriate nutrient solutions were applied to each plot with an independent drip-irrigation system. There was a guard row of plants at each side of the experiment. Nitrogen (185 mg L 1 NO3-N and 15 mg L 1 NH4-N), phosphorus (50 mg L 1 ), potassium (390 mg L 1 ), iron (7 mg L 1 ), manganese (0.8 mg L 1 ), zinc (0.16 mg L 1 ), copper (0.05 mg L 1 ) and boron (0.52 mg L 1 ) were included in all nutrient solutions. To equalize the electrical conductivity (EC) of nutrient solutions across treatments (to avoid confounding the effects of EC with treatments), the concentrations of chloride (Cl), sulphur (S) and sodium (Na) were allowed to vary in the range of , and mg L 1, respectively. The variations of Cl, S and Na in these ranges of concentration would not have any significant effect on greenhouse tomatoes (Lopez et al. 1996; Voogt and Sonneveld 1997; Nukaya and Hashimoto 2000). The final EC of all nutrient solutions was 3 ± 0.2 ds m 1. The ph of the nutrient solutions was adjusted to 5.8 by adding diluted nitric acid. Plant Growth, Leaf Chlorosis and Photosynthesis Leaf area and dry weight and gas exchange parameters of the fifth youngest fully expanded leaf were measured on three plants in each plot. Gas exchange parameters of representative leaves (healthy or with an average severity of chlorosis) in the mid-canopy were also measured. The leaf area was measured with a LI-COR 3100 leaf area meter

3 HAO AND PAPADOPOULOS CALCIUM AND MAGNESIUM ON GREENHOUSE TOMATO 905 Table 1. Leaf chlorosis and root-health rating of tomato plants grown at different Ca/Mg concentrations in 1999 z Leaf area and dry weight Leaf chlorosis (%) y Root rating (13 Dec. ) w Ca/Mg (mg L 1 ) 27 Oct. 29 Nov. 13 Dec. (%) x cm 2 leaf 1 g leaf 1 150/ a 22.8b 17.9b 9.1b 2376b 7.0b 150/50 9.3b 2.9c 0.0c 8.4b 2088b 6.5b 150/80 3.8bc 1.9c 2.5c 18.8b 2245b 6.7b 150/ bc 0.8c 0.0c 17.8b 2291b 6.7b 300/ a 40.6a 46.4a 14.3b 1884b 5.4b 300/50 7.1bc 2.1c 1.6c 20.1b 2493b 7.5ab 300/80 1.0c 1.8c 1.0c 50.3a 3317a 10.1a 300/ bc 0.3c 0.0c 20.3b 2474b 7.5ab Factors and their interaction w Ca NS NS * * NS NS Mg ** ** ** * * NS Ca Mg NS NS ** NS ** NS Regression on Mg (mg L 1 ) Ca (mg L 1 ) R 2 (%) Leaf chlorosis 27 Oct. 150/ X X ** 29 Nov. 150/ X X ** 13 Dec X 33.3* 13 Dec X X ** Leaf area (cm 2 leaf 1 ) 13 Dec X X ** Leaf dry weight (cm 2 leaf 1 ) 13 Dec X X * z Means within each column followed by different letters are significantly different (P < 0.05) according to Duncan s multiple range test. y Percentage of foliage showing leaf chlorosis. x Percentage of under-surface area of rockwool slabs covered by healthy (white) roots at the end of the experiment. Means presented are averages of four slabs. w There was no significant difference in the leaf area and weight of fifth youngest fully expanded leaf measured on 22 September and 30 November *, **Significant (0.01< P < 0.05) or highly significant (P < 0.01), respectively; NS, not significant (P > 0.05) (LI-COR Inc., Lincoln, NE 68504, USA) and leaf dry weight was determined after drying at 65 C for 2 3 wk. Gas exchange parameters were measured with a LI-COR 6400 portable photosynthesis system (LI-COR Inc., Lincoln, NE 68504, USA) equipped with the LI-COR LED light source in mid to late October. To reduce the influence of diurnal change on leaf photosynthesis, the measurements were conducted between 1000 and Leaf Mg and Ca deficiency was monitored monthly on 10 plants per treatment plot. Fruit Harvest and Quality Analysis Fruits, at the breaker stage, were harvested two to three times a week, from 13 September to 14 December, The harvested fruits were graded as grade #1: extra large, large, and small; commercial; grade#2; and unmarketable: blossom-end rot (BER) and catfaced (CF) and other unmarketables, according to commercial grading standards (Ontario Ministry of Agriculture and Food, Regulation 378/90, 1987). The fruits were also graded biweekly for russeting (cuticle cracking). Russeting was recorded according to a 10-grade scale [modified from Emmons and Scott (1997)]: [Grade 0: glossy, no russeting at all; Grades1 4: no lesions visible (lesions are the fine cracks large enough to form a scar on the crack), hair-like cracks covered not over half of fruit shoulder (1), beyond half but not over fruit shoulder (2), extending beyond fruit shoulder but not over the middle of the fruit (3), over the middle of the fruit (4); Grades 5 9: 0 2.5%, 12.5 to 25%, 25 to 37.5%, 37.5 to 50%, >50% area of fruit shoulder with lesions or 0 25%, 25 50%, 50 75%, % of fruit shoulder with discolouration (gray colour tissue under the epidermis), respectively]. Levels 1 3 russeting usually do not cause the fruit to be downgraded while level 4 and above do cause the fruit to be downgraded from grade #1 to #2. An overall russeting index was calculated by summing up the product of percent fruit weight in each grade times the rating grade number. Fruit quality parameters (fruit dry matter content and soluble solids) were measured monthly. For quality analysis, four large or extra-large fruit of grade #1 in breaker stage were randomly selected from each plot, then stored at 20 C and 70% relative humidity until the table-red stage. Fruit dry matter content was measured by drying sliced fruits at 65 C for 3 wk. Soluble solids were measured with a portable digital refractometer (model PR-101, Atago Co., Tokyo, Japan) in homogenized fruit samples. Mechanical Properties of Fruit Fruit firmness was tested by constant area compression and puncture tests. The fruits used for firmness tests were kept at 20 C for 1 d to allow them to ripen to the pink stage (US Department of Agriculture 1973). It was easy to select fruit from breaker to pink stages in order to get uniformity in ripening. For the constant area compression test, three pericarp specimens from each tomato were taken around the fruit equator and over the locule using a 12-mm core borer (Jackman et al. 1990). The specimens were uniformly light pink with no green colour visible. Each specimen, with intact epidermal tissue,

4 906 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 1. Leaf photosynthesis and stomatal conductance of healthy and Mg-deficient (average severity of leaf chlorosis) leaves in mid-canopy. Mean of 10 leaflets, measured with LI-COR 6400 portable photosynthesis system (Lincoln, Nebraska, USA) with a LI-COR LED light source at 300 µmol m 2 s 1 PPFD, 65% relative humidity, 25 C temperature and ambient concentration of carbon dioxide on 28 October. Different letters above the bars indicate a significant difference (P < 0.05). was put on a flat metal platform and compressed at a speed of 10 mm min 1 with a 57-mm flat-ended cylindrical mandrel mounted on an Instron Model 4411 Testing machine (Instron Canada, Burlington, ON, Canada) equipped with a 50- N load cell. Force-displacement data acquisition was at 10 points per second. The raw data were used as inputs for the Instron Series IX software, which produced a force vs. displacement curve for the specimen and other outputs, including maximum force for tissue collapse /failure (MF), slope of the curve in the linear stage (SLOPE) and the total energy required for tissue collapse, i.e., the area under the force-displacement curve up to tissue failure point. For the measurement of firmness by the puncture test, each fruit was placed on a flat plate and punched around the equator in three places using a cylindrical probe (1 mm in diameter) (Holt 1970). Data Analysis Data were analysed with the SAS General Linear Models procedure (GLM). Analysis of variance was first conducted. If the treatment effects were significant, then their means were separated with Duncan s multiple-range test. A polynomial model was used for regression analysis of selected parameters on Mg concentrations when the P value for the Mg effect in the analysis of variance was < Separate regression analysis was conducted for each level of Ca if the Ca Mg interaction was significant in the analysis of variance. The regression model was fitted with a backward elimination method and a P value of 0.15 was used to decide whether a model term should be dropped from the model during the fitting process. The partial R 2 (R 2 Mg ), which measured the strength of the relationship between the response variable and Mg concentration after adjusted for calcium and replicate(block) effects, was calculated for the final regression. Significance of the R 2 Mg was determined by an F -test (Hao 1995): F = (R 2 Mg ) (error-df))/((1 R2 Mg ) Mg df) with Mg df, error-df.

5 HAO AND PAPADOPOULOS CALCIUM AND MAGNESIUM ON GREENHOUSE TOMATO 907 Table 2. Fruit yield, grades and size of tomato grown at different Ca/Mg concentrations in 1999 z Ca/Mg Total fruit weight (kg plant -1 ) Marketable yield (kg plant -1 ) Marketable fruit Marketable y BER fruit weight (%) y (mg L 1 ) Before 1 Nov. After 1 Dec. Total Before 1 Nov. After 1 Dec. size (g fruit -1 ) fruit weight (%) Before 1 Nov. After 1 Dec. 150/ ab 1.54 cd 4.58 cd 1.84bc 1.49bc c 92.5ab 10.1b 2.3abc 150/ b 1.34d 4.22d 1.73bc 1.25c 140.8bc 88.7bc 13.0ab 6.7a 150/ ab 1.49d 4.47cd 1.62c 1.40c 141.2bc 84.6cd 21.1a 6.3ab 150/ ab 1.57bcd 4.70abc 1.62c 1.47bc 142.2ab 83.4d 22.5a 6.3ab 300/ ab 1.58abcd 5.04abc 2.11ab 1.53abc 146.4ab 93.7a 7.1b 1.7bc 300/ a 1.83abc 5.60a 2.30a 1.80ab 149.8a 96.8a 3.1b 0.3c 300/ ab 1.90a 5.40ab 1.97abc 1.87a 147.7ab 93.2ab 10.6b 0.3c 300/ ab 1.87ab 5.46a 2.05ab 1.86a 140.3bc 93.7a 10.0b 0.5c Factors and their interaction y Ca ** ** ** ** ** ** ** ** ** Mg NS NS NS NS NS NS * * NS Ca Mg NS NS NS NS NS NS * NS NS Regression on Mg (mg L 1 ) Ca (mg L 1 ) R 2 (%) Marketable fruit (%) X 53.4** BER fruit (%), before 1 Nov X 53.2** Total fruit weight (g plant 1 ), after 1 Dec X X * Marketable yield (g plant 1 ), after 1 Dec X X * z The data presented are means of 40 plants per treatment (four replicates)). Means in the same column followed by different letters are significantly different (P < 0.05) according to Duncan s multiple range test. y Percentage over total fruit weight. *, ** Significant (0.01< P < 0.05) or highly significant (P < 0.01), respectively; NS, not significant (P > 0.05).

6 908 CANADIAN JOURNAL OF PLANT SCIENCE Table 3. Fruit soluble solids (SS) and dry matter content (DW) of tomato grown at different Ca/Mg concentrations in 1999 z Ca/Mg 28 Sept. 10 Nov. 16 Dec. (mg L 1 ) SS (Brix, %) DW (%) SS (Brix, %) DW (%) SS (Brix, %) DW (%) 150/ a 5.14ab 4.41a 5.55a 5.53ab 5.00abc 150/ a 5.46a 4.57a 5.51a 5.79a 5.26a 150/ a 4.78bc 4.74a 5.47a 5.21bc 5.21ab 150/ a 4.88bc 4.48a 5.26ab 5.20bc 5.10ab 300/ b 4.73bc 4.14a 4.88b 5.18bc 4.61c 300/ ab 4.47c 4.31a 5.07ab 5.18bc 4.96abc 300/ ab 4.6bc 4.18a 5.01ab 4.90c 4.78bc 300/ a 4.38c 4.27a 5.09ab 5.00c 4.87abc Factors and their interaction z Ca * ** ** ** ** ** Mg NS NS NS NS ** NS Ca Mg NS NS NS NS NS NS Regression on Mg (mg L 1 ) Ca (mg L 1 ) R 2 (%) 28 Sept. SS (Brix, %) 150/ X 14.4* DW(%) 150/ X 21.0* 16 Dec. SS (Brix, %) X 41.6* z Means in the same column followed by different letters are significantly different (P < 0.05) according to Duncan s multiple range test. *, **Significant (0.01< P < 0.05) or highly significant (P < 0.01), respectively; NS, not significant (P > 0.05). Where Mg-df was the degrees of freedom for all Mg terms, and error-df was the degrees of freedom for error. Only the final regression functions that were significant (P < 0.05) are reported. RESULTS AND DISCUSSION Mg Deficiency and Photosynthesis Plants started to show symptoms of Mg deficiency 8 wk after planting when about 1.5 m high. Treatment 300/20 (Ca/Mg, mg L 1 ) was the first to show the symptoms of Mg deficiency (leaf chlorosis), and had the most severe symptoms (Table 1). Beginning on 27 October, the lowest Mg treatments were consistently the most chlorotic. On the two later sampling dates, the plants at 300/20 treatment were significantly more chlorotic than at the 150/20 treatment, with a significant interaction of Ca and Mg at the last sampling date (13 December). Treatments with higher than 50 mg L 1 Mg showed little or no Mg deficiency symptoms. No visible leaf Ca-deficiency symptoms were observed in the experiment. The Mg-deficiency symptoms appeared not only on bottom leaves, but also on the top and middle leaves. In contrast to conventional thought, the most severe Mg-deficient symptoms occurred on the middle leaves instead of the bottom leaves. The occurrence of Mg deficiency on the middle leaves was also found by Sonneveld and Voogt (1991) in a fall greenhouse tomato crop. The occurrence of Mg deficiency on the middle leaves could significantly affect the photoassimilate production and supply to other parts of the plants. The photosynthesis and stomatal conductance of leaves with moderate Mg deficiency (average severity of leaf chlorosis) in the middle canopy were about 50 70% lower than those of normal leaves (without leaf chlorosis, Fig. 1). There were no significant differences among treatments in gas exchange of the fifth youngest fully expand leaf (no leaf chlorosis) regardless of nutrient treatment. The leaf photosynthesis of the fifth youngest fully expanded leaf, measured on a sunny day [15 October 1999; at 1000 µmol m 2 s 1 photosynthestic photon flux density (PPFD), 65% RH, 25 C and ambient CO 2 concentration], or on a fully cloudy day (21 October 1999; at 300 µmol m 2 s 1 PPFD, 65% RH, 25 C and ambient CO 2 concentration), did not reveal any significant differences among nutrient treatments (P > 0.05, data not shown). In the late growth stage, leaf size and dry weight were affected by the Mg concentration at 300 mg L 1 Ca; the 300/80 mg L 1 Ca/Mg treatment had the largest and heaviest leaves (Table 1). At the end of the experiment, the root systems at 300/80 mg L 1 Ca/Mg were also rated the best (Table 1). The growth of tomato roots depends strongly on their supply of carbohydrates (Ho and Adams 1995). With the largest leaves and no leaf chlorosis at 300/80 mg L 1 Ca/Mg, it could be expected that the carbohydrate supply to the root systems would be higher than in the other nutrient treatments late in the experiment. High Ca (300 mg L 1 ) increased leaf chlorosis on the last sampling date (13 December) but only at the lowest Mg concentration, and improved root rating at the end of the experiment (Table 1). There was a significant Ca Mg interaction on leaf chlorosis and leaf size on the last sampling date; leaf size was not affected by Mg concentration at 150 mg L 1 Ca but it was at 300 mg L 1 Ca. Fruit Yield and Grades High Ca (300 mg L 1 ) resulted in higher total and marketable fruit yield, larger fruit size, higher percentage of marketable fruit, and lower incidence of BER, in comparison to low Ca (150 mg L 1 ) (Table 2). Mg concentration did not affect total and marketable fruit yield or fruit size at 150 mg L 1 Ca. Incidence of BER fruit increased linearly with increasing Mg concentration at 150 mg L 1 Ca, but had little such effect at 300 mg L 1 of Ca. The high BER inci-

7 HAO AND PAPADOPOULOS CALCIUM AND MAGNESIUM ON GREENHOUSE TOMATO 909 Fig. 2. Maximum force (MF, Newton) for pericarp tissue failure at different Ca/Mg treatments in A. Regression at 150 mg L 1 Ca: Y = Mg Mg X (pericarp thickness, mm), n = 16, R 2 = 74.3%*. B. Regression at 150 mg L 1 Ca: Y = Mg Mg X Z (fruit weight, g fruit 1 ), n = 16, R 2 = 9 3.6%**. The regression lines were plotted at the average pericarp thickness or fruit weight for each nutrient treatment. dence resulted in linear decline in the percentage of marketable fruit with increasing Mg concentration. At 300 mg L 1 Ca, Mg concentration affected fruit production in late fruit production (after 1 December). The marketable yield at 20 mg L 1 Mg after 1 December tended to be lower. Magnesium is a critical component of chlorophyll, which is essential for the light reaction of photosynthesis (Taiz and Zeiger 1998). In a previous study on winter tomato crops, low Mg concentration significantly reduced fruit yield in winter time (Hao and Papadopoulos, data not published). However, in a fall tomato crop (this study), the yield reduction was much smaller. The average solar radiation in the last 2 mo of the winter crops ( 5 MJ m 2 d 1, Hao and Papadopoulos, data not published) was only half of the radi-

8 910 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 3. Slope of force vs. deformation curve (Newton mm 1 ) of the pericarp tissue at different Ca/Mg treatments in A. Regression at 150 mg L 1 Ca: Y = Mg Mg X (pericarp thickness, mm) Z (fruit weight, g fruit 1 ), n = 16, R 2 = 91.6%*. B. Regression at 150 mg L 1 Ca: Y = Mg Mg X Z, n = 16, R 2 = 93.3%**. The regression lines were plotted at the average pericarp thickness and fruit weight for each nutrient treatment. ation in this study (10 MJ m 2 d 1 ). Under the limited light conditions, reductions in light reaction efficiency with low chlorophyll caused by low Mg concentration were likely more harmful, and thus resulted in larger yield loss in the winter crops. Under high light conditions, as in this study, the interception of light was less critical for photosynthesis, and thus had less impact on plant growth and fruit yield. There was a high incidence of BER in early fruit production. BER is a fruit Ca-deficiency and stress-related disorder (Saure 2001). Any factors that increase fruit Ca demand and reduce Ca transport to fruit would increase the incidence of BER (Ho et al. 1999). This fall experiment was characterized by strong solar radiation, high air temperature, and strong air movement in the early growth stage, i.e., a stress-

9 HAO AND PAPADOPOULOS CALCIUM AND MAGNESIUM ON GREENHOUSE TOMATO 911 ful environment. The strong solar radiation and high air temperature would likely increase fruit growth and thus increase the demand for Ca while strong air movement would increase leaf transpiration and thus the competition between fruit and leaves for Ca. High concentrations of Ca have been known to increase the tolerance of plants to stress (Fletcher et al. 2000), and it is conceivable that this may have led to the higher yields in our study. Fruit Quality and Mechanical Properties High Ca (300 mg L 1 ) reduced fruit soluble solids and fruit dry matter content in comparison to low Ca (150 mg L 1 ) (Table 3). Magnesium concentration had a minor effect on fruit soluble solids. High Mg increased fruit soluble solids in the early fruit production period while it reduced it in the last month of fruit harvest. The response of firmness parameters such as toughness, total energy, maximum force for breaking pericarp (MF) and the slope of the force-deformation curve (SLOPE) to Ca and Mg treatments was similar. Therefore, only the data on MF and SLOPE are presented (Figs. 2 and 3). High Ca reduced both MF and the SLOPE in both early and late fruit production periods. The Mg effects on MF and SLOPE varied with Ca concentration and fruit production period. In the early and middle fruit production periods, the MF first increased with increasing Mg concentration and then levelled off at 80 mg L 1 Mg at 150 mg L 1 Ca, while there was no response to Mg concentration at 300 mg L 1 Ca. Similarly, at 150 mg L 1 Ca, SLOPE increased with Mg concentration in the early and middle fruit production periods, but there was no response at 300 mg L 1 Ca. The MF and SLOPE were higher at 80 mg L 1 Mg than at 50 mg L 1 Mg at both 150 and 300 mg L 1 Ca in the late production period. The puncture test did not reveal any treatment effects except for an increase in MF by the high Ca at the last measurement (9 December 1999, data not shown). High Ca (300 mg L 1 ) reduced fruit russeting in middle and late fruit production (Table 4). Magnesium concentration affected fruit russeting only in November. There was a significant interaction between Ca and Mg on fruit russeting in November; at 150 mg L 1 Ca, russeting was the most severe at 50 mg L 1 Mg, but at 300 mg L 1 Ca, it was the least severe at 50 mg L 1 Mg. Calcium is well known for its role in maintaining the cell wall, particularly the middle lamella structure, through its binding to pectic substances. This property has long been used in maintaining tissue integrity of processed tomato products (Barrett et al. 1998). However, the effects of Ca concentration during cultivation on tomato fruit texture are far from conclusive and most studies have not demonstrated an improvement in textural properties (Barrett et al. 1998). The application of Ca at 250 kg ha 1 every week or every 2 weeks increased fruit firmness of tomato grown on Courval sandy loam soil (Dodds et al. 1997). Calcium foliar spray increased firmness of tomatoes stored at different temperatures (Garcia et al. 1995). However, the presence of high levels of Ca in the fruit negatively affects the organoleptic quality, firmness and shelf life of greenhouse tomato (De Kreij 1995; Ho et al. 1999). Therefore, it may Table 4. Fruit russeting index of tomato grown at different Ca/Mg concentrations in 1999 z Ca/Mg(mg L 1 ) Nov. Dec. 150/ b 0.57ab 150/ a 0.82a 150/ bc 0.49ab 150/ bc 0.68ab 300/ bc 0.22b 300/ c 0.51ab 300/ bc 0.30b 300/ c 0.25b Factors and their interaction z Ca ** ** Mg * NS Ca Mg ** NS z Index was calculated by summing up the product of percent fruit weight in each grade times the rating grade number. Means in the same column followed by different letters are significantly different (P < 0.05) according to Duncan s multiple range test. There was no significant difference on russeting among treatments in September and October. *, **Significant (0.01< P < 0.05) or highly significant (P < 0.01), respectively; NS not significant (P > 0.05). be safe to say that additional Ca improves fruit firmness under low Ca conditions, such as in the field (Dodds et al. 1997), but additional Ca reduces fruit firmness under high Ca reduced conditions, as found in some greenhouse tomato production systems. Additional supply of Ca has been found to prevent tomato fruit cracking (Simon 1978). In this study, the higher level of Ca reduced MF for breaking pericarp and the slope of the force-deformation curve (SLOPE) for breaking pericarp, but increased the MF for puncturing the fruit epidermis, and reduced russeting incidence and severity. Therefore, increased calcium seems to be maintaining tissue integrity and increasing tissue elasticity, rather than increasing tissue rigidity. CONCLUSIONS High Ca (300 mg L 1 ) improved tomato fruit yield, and reduced incidence of BER and fruit russeting in a fall tomato crop, while it reduced firmness of pericarp tissue. The positive effects of yield improvement and reduction in BER and russeting should outweigh the negative impact on fruit soluble solids and firmness, because the latter two are not major quality concerns in fall production. Therefore, higher Ca concentrations are recommended, at least for fall tomato production. Low Mg (20 ppm) caused leaf chlorosis in middle leaves and tended to reduce fruit yield in late fruit production. High Mg increased fruit BER incidence and russeting severity, mainly at 150 mg L 1 Ca, but it did not offer any yield advantage in the early production period. However, 80 mg L 1 Mg improved root growth, leaf size and fruit firmness in late production at 300 mg L 1 Ca. Fruit yield was the highest at 300/50 80 mg L 1 Ca/Mg. Fruit russeting was the lowest at 300/50 mg L 1 Ca/Mg in the middle fruit production. Therefore, for a fall greenhouse tomato crop, the optimum Ca/Mg management strategy seems to be starting at 300/50 mg L 1 Ca/Mg and gradually increasing Mg to 80 mg L 1 towards the end of the season to improve plant growth and fruit firmness.

10 912 CANADIAN JOURNAL OF PLANT SCIENCE ACKNOWLEDGEMENTS This research was supported in part by the Ontario Greenhouse Vegetable Growers. We thank R. Paine and J. Blackburn for invaluable technical support. Adams, P Some effects of the environment on the nutrition of greenhouse tomatoes. Acta Hortic. 366: Adams, P. and el-gizawy, A. M Effect of calcium stress on the calcium status of tomatoes grown in NFT. Acta Hortic. 222: Adams, P. and Holder, R Effects of humidity, Ca and salinity on the accumulation of dry matter and Ca by the leaves and fruit of tomato (Lycopersicon esculentum). J. Hortic. Sci. 67: Barrett, D. M., Garcia, E. and Wayne, J. E Textural modification of processing tomatoes. Crit. Rev. Food Sci. Nutr. 38: De Kreij, C Latest insights into water and nutrient control in soilless cultivation. Acta Hortic. 408: De Kreij, C., Janse, J., van Goor, B. J. and van Doesburg, J. D. J The incidence of calcium oxalate crystals in fruit walls of tomato (Lycopersicon esculentum Mill) as affected by humidity, phosphate and calcium supply. J. Hortic. Sci. 67: Den Outer, R. W. and van Veenendaal, W. H. L Gold speckles in tomato fruits (Lycopersicon esculentum Mill). J. Hortic. Sci. 63: Dodds, G. T., Trenholm, L. Rajabipour, A. Madramootoo, C. A. and Norris, E. R Yield and quality of tomato under water-table management. J. Am. Soc. Hortic. Sci. 122: Dorais, M., Papadopoulos, A. P. and Gosselin, A Greenhouse tomato fruit quality. Hortic. Rev. 26: Emmons, C. L. and Scott, J. W Environmental and physiological effects on cuticle cracking in tomato. J. Am. Soc. Hortic. Sci. 122: Fletcher, R. A., Gilley, A., Sankhla, N. and Davis, T. D Triazoles as plant growth regulators and stress protectants. Hortic. Rev. 24: Garcia, J. L., Ruiz-Altisent, M. and Barriero, P Effect of foliar applications of CaCl 2 on tomato stored at different temperatures. J. Agr. Food Chem. 43: Hao, X The effects of UV-B radiation and its interactions with carbon dioxide and ozone on tomato (Lycopersicon esculentum Mill cv. New Yorker). Ph.D. dissertation, University of Guelph, Guelph, ON. 244 pp. Ho, L. C. and Adams, P Nutrient uptake and distribution in relation to crop quality. Acta Hortic. 396: Ho, L. C., Hand, D. J. and Fussell, M Improvement of tomato fruit quality by calcium nutrition. Acta Hortic. 481: Holder, R. and Cockshull, K. E Effect of humidity on the growth and yield of glasshouse tomatoes. J. Hortic. Sci. 65: Holt, C. B Measurement of tomato firmness with a universal testing machine. J. Text. Stud. 1: Jackman, R. L., Marangoni, A. G. and Stanley, D. W Measurement of tomato fruit firmness. HortScience 25: Janse, J Goudspikkels bij tomaat; een oplosbaar probleem. Groenten en Fruit 43: Lopez, J., Tremblay, N. Voogt, W., Dube, S. and Gosselin, A Effects of varying sulphate concentrations on growth, physiology and yield of the greenhouse tomato. Sci. Hortic. 67: Nukaya A. and Hashimoto, H Effects of nitrate, chloride and sulfate ratios and concentration in the nutrient solution on yield, growth and mineral uptake characteristics of tomato plants grown in closed rockwool system. Acta Hortic. 512: Ontario Ministry of Agriculture, Food and Rural Affairs, Fruit and Vegetable Inspection Branch Greenhouse tomato grading and packing manual, from Regulation 378/90, the Farm Products Grades and Sales Act. OMAFRA, Toronto, ON. 8 pp. Paiva, E. A. S., Sampaio, R. A. and Martinez, H. E. P Composition and quality of tomato fruit cultivated in nutrient solutions containing different calcium concentrations. J. Plant Nutr. 21: Papadopoulos, A. P Growing greenhouse tomatoes in soil and in soilless media. Agriculture and Agri-Food Canada, Ottawa, ON. Publ. 1865/E, 79 pp. Papadopoulos. A. P. and Hao, X Interactions between nutrition and environmental conditions in hydroponics. Pages in D. Savas and H. Passam, eds. Hydroponic production of vegetables and ornamentals. Embryo Publications, Athens, Greece. Papadopoulos, A. P. and Liburdi, N The Harrow Fertigation Manager, a computerized multifertilizer injector. Acta Hortic. 260: Saure, M. C Blossom-end rot of tomato (Lycopersicon esculentum Mill) a calcium- or stress related disorder? Sci. Hortic. 90: Simon, E. W The symptoms of calcium deficiency in plants. New Phytol. 80: Sonneveld, C Magnesium deficiency in rockwool-grown tomatoes as affected by climatic conditions and plant nutrition. J. Plant Nutr. 10: Sonneveld, S. and Voogt, W Effects of Ca-stress on blossom-end rot and Mg-deficiency in rockwool grown tomato. Acta Hortic. 294: Taiz, L. and Zeiger, E Plant physiology. 2nd ed., Sinauer Associates, Inc., Publishers, Sunderland, MA. 792 pp. US Department of Agriculture United States standards for grades of fresh tomatoes. Effective 1 Dec (38 F.R ) as amended 29 Nov (38 F.R ) and 1 Feb (40 F.R. 2791). USDA, Agricultural Marketing Service, Washington, DC. Voogt, W. and Sonneveld, C Nutrient management in closed growing systems for greenhouse production. Pages in E. Goto, K. Kurate, M. Hayashi, and S. Sase, eds. Plant production in closed ecosystems. Kluwer Academic Publishers, Dordrecht, The Netherlands.

11 This article has been cited by: 1. Dania Israr, Ghulam Mustafa, Khalid Saifullah Khan, Muhammad Shahzad, Niaz Ahmad, Sajid Masood Interactive effects of phosphorus and Pseudomonas putida on chickpea ( Cicer arietinum L.) growth, nutrient uptake, antioxidant enzymes and organic acids exudation. Plant Physiology and Biochemistry 108, [Crossref] 2. Rita Leogrande, Ornella Lopedota, Carolina Vitti, Domenico Ventrella, Francesco Montemurro Saline water and municipal solid waste compost application on tomato crop: Effects on plant and soil. Journal of Plant Nutrition 39:4, [Crossref] 3. T. Casey Barickman, Dean A. Kopsell, Carl E. Sams Foliar applications of abscisic acid decrease the incidence of blossomend rot in tomato fruit. Scientia Horticulturae 179, [Crossref] 4. Jóska Gerendás, Hendrik Führs The significance of magnesium for crop quality. Plant and Soil 368:1-2, [Crossref] 5. Francisco M. del Amor, Jose S. Rubio Effects of Antitranspirant Spray and Potassium: Calcium: Magnesium Ratio on Photosynthesis, Nutrient and Water Uptake, Growth, and Yield of Sweet Pepper. Journal of Plant Nutrition 32:1, [Crossref]