David L. Ehret

Tomato (Solanum lycopersicum) health components: from the seed to the consumer

It is widely accepted that a healthy diet is an important factor in preventing chronic diseases, and in improving energy balance and weight management. Studies have shown strong inverse correlations between tomato consumption and the risk of certain types of cancer, cardiovascular diseases and age-related macular degeneration. Because tomato is the second-most important vegetable in the world after potato, this horticultural crop constitutes an excellent source of health-promoting compounds due to the balanced mixture of minerals and antioxidants including vitamins C and E, lycopene, β-carotene, lutein and flavonoids such as quercetin. Improvement in phytonutrients in tomatoes can be achieved by cultivar selection, environmental factors, agronomic practices, stage of ripeness at harvest, and appropriate handling and conditioning all the way from the field to the consumer. The purpose of this paper is to review the recent literature of the main factors that can improve the nutritional quality of tomato and consequently their beneficial role in human diet. The importance of genotype selection and the optimization of environmental conditions (light, temperature, humidity, atmospheric CO2 and air pollutants) for high nutritional value is outlined first, followed by the optimization of agricultural practices (soil properties, water quality, mineral nutrition, salinity, grafting, pruning, growing systems, growth promoters, maturity, and mechanical and pest injuries). The review concludes by identifying several prospects for future research such as modelling and genetic engineering of the nutritional value of tomato.

Inoculation with arbuscular mycorrhizal fungi improves the nutritional value of tomatoes

Arbuscular mycorrhizal (AM) fungi can affect many different micronutrients and macronutrients in plants and also influence host volatile compound synthesis. Their effect on the edible portions of plants is less clear. Two separate studies were performed to investigate whether inoculation by AM fungi (Rhizophagus irregularis, Funneliformis mosseae, or both) can affect the food quality of tomato fruits, in particular common minerals, antioxidants, carotenoids, a suite of vitamins, and flavor compounds (sugars, titratable acids, volatile compounds). It was found that AM fungal inoculation increased the nutrient quality of tomato fruits for most nutrients except vitamins. Fruit mineral concentration increased with inoculation (particularly N, P, and Cu). Similarly, inoculated plants had fruit with higher antioxidant capacity and more carotenoids. Furthermore, five volatile compounds were significantly higher in AM plants compared with non-AM controls. Taken together, these results show that AM fungi represent a promising resource for improving both sustainable food production and human nutritional needs.

Foliar applications of fertilizer salts inhibit powdery mildew on tomato

Foliar applications of a number of inorganic fertilizer salts were found to significantly reduce powdery mildew [Erysiphe orontii] on greenhouse tomato (Lycopersicon esculentum, cv. Trust) leaves. In a series of single-application experiments, the foliar applications, each with 0.1% surfactant, were applied to the third and fourth leaves of young tomato plants 24 h before inoculation with an atomized application of mildew conidia. Control treatments consisted of a water application and a water plus surfactant application. Powdery mildew colonies were counted 7–10 days later. Surfactant alone significantly reduced mildew colony numbers. CaCl2, Ca(NO3)2, and K2HPO4 reduced colony counts compared with the surfactant alone. All combinations of Ca salts, or Ca salts plus elemental S, significantly reduced mildew colony counts compared with surfactant alone. In a second set of experiments, the effects of repeated applications on already naturally infected tomato plants were evaluated. Young tomato plants were moved to a greenhouse containing several heavily mildew-infected tomato plants, allowing natural infection. The following day and every 7–10 days thereafter, treatments were applied to all leaves. Colony counts on selected leaves were made weekly or just before spraying. Surfactant alone was not as effective as in the single-application treatments, often having no effect. All the Ca-salt treatments that were effective in the single-application series were effective as multiple applications. Repeated applications of combinations of Ca salts were often just as effective as applications of elemental S. KCl, MgSO4, and K2HPO4 also significantly reduced mildew counts with multiple applications. This study did not attempt to explain the differences or similarities in efficacy of the salts tested; both osmotic (concentration) and specific-ion effects could play a role.Key words: surfactant, Erysiphe orontii, Lycopersicon esculentum, greenhouse, calcium, potassium, sulphur, magnesium, powdery mildew.

Tomato Fruit Antioxidants in Relation to Salinity and Greenhouse Climate

A two-year study of antioxidants in greenhouse tomato was conducted. Plants were treated continuously with nutrient solution electrical conductivities (EC) of 2, 4, or 6 dS m⁻¹. Increasing EC reduced yield per plant and fruit size. Oxygen radical absorbance capacity (ORAC), lutein, β-carotene, lycopene, and vitamin C concentrations were evaluated in harvested fruit. ORAC and all antioxidants with the exception of lutein increased with EC. None of the 10 genes involved in antioxidant metabolism were affected by salinity in ripe fruit, but the expression of three of them (ZDS, CrtR-b1, and NCED1) varied with the stage of fruit development. Antioxidant concentrations were related to greenhouse climatic conditions. β-Carotene, lycopene, lutein, and vitamin C responded negatively to light and positively to temperature, whereas ORAC was unresponsive. Multiple regressions of antioxidants in relation to EC and climatic factors showed that antioxidants responded more strongly to light and temperature than to EC.

Host range of a powdery mildew (Erysiphe orontii) on tomato.

A powdery mildew disease of greenhouse tomato first appeared in the Fraser Valley of British Columbia in 1995. The causal agent was identified as Erysiphe orontii. Host range studies were conducted using uniform levels of inoculum of the pathogen under greenhouse conditions. Of 26 tomato cultivars inoculated, cv. DRW4409F1 had the least powdery mildew infection. Twenty-five of the 26 tomato cultivars tested, as well as eggplant cv. Early Long Purple, nightshade and tomatillo, were susceptible to E. orontii. Tobacco and potato (cv. Epicure) had slight infection. Cultivars of pepper, potato, corn, strawberry, raspberry, bean, feverfew, borage, delphinum, petunia, impatiens, gazania, morning glory, zinnia, african daisy, cosmos, wild buckwheat, curled dock, and knotweed were not susceptible to E. orontii. This study indicates that resistance to powdery mildew of tomato is available and should be explored in breeding programs to develop powdery mildew-resistant cultivars for the greenhouse industry. Key words...

Effects of nitrogen rate and application method on early production and fruit quality in highbush blueberry

Ehret, D. L., Frey, B., Forge, T., Helmer, T., Bryla, D. R. and Zebarth, B. J. 2014. Effects of nitrogen rate and application method on early production and fruit quality in highbush blueberry. Can. J. Plant Sci. 94: 1165–1179. Proper nitrogen (N) fertilizer management of highbush blueberry (Vaccinium corymbosum L.) is of major importance in south-coastal British Columbia, but little information is available. A field study was conducted to examine the effects of N rate and method of application on growth, yield, and fruit quality in highbush blueberry during the first 4 yr after planting in south-coastal BC. Nitrogen was applied at 0–150% of current production guide rates either with three equal applications of broadcast granular ammonium sulphate each spring or by fertigation through the drip irrigation system with 10 equal applications of liquid ammonium sulphate injected every 2 wk from early spring to late summer each year. Yield increased with increasing N rate during the second and third years of fruit production. The yield response as well as flower number and plant size were greater with fertigation than with broadcast fertilizers. Fruit firmness also increased consistently with increased N rates, while fruit size either increased or decreased, depending on year. There were no effects of N on fruit oxygen radical absorbance capacity (ORAC), titratable acidity, or soluble solids. However, the composition of fruit anthocyanins changed, with concentrations of seven anthocyanins decreasing, and three others increasing, with N rate. In 2 of 3 yr, total anthocyanin concentration was greater in fertigated than in broadcast treatments. Soil ammonium and nitrate concentrations increased with N rate, but only soil nitrate differed between the two application methods. Soil nitrate was higher with fertigation than with granular fertilizers, particularly at the end of the season and when greater rates of N were applied. In summary, fertigation produced more shoot growth and greater yields with less N than broadcast applications of fertilizer.

A new wood fibre substrate for hydroponic tomato and pepper crops

The use of red cedar sawdust as a growing substrate for hydroponic tomato and pepper production was tested by comparison with yellow cedar sawdust and coir. In experiments with 14-d-old transplants, growth inhibition was observed in response to red cedar compared with yellow cedar sawdust. However, growth of plants transplanted at 28 d was better in red cedar than in yellow cedar, and those planted at 38 d were unaffected by sawdust type. Additionally, tomato and pepper plants grown to maturity under conditions similar to commercial production systems showed no negative effects of red cedar on fruit yield or quality when compared with plants grown in either yellow cedar or coir. There were also no differences in plants grown in either new or old red cedar sawdust. The data suggest that western red cedar should be considered as a viable substrate for production of greenhouse vegetable crops. Key words: Western red cedar, tomato, pepper, hydroponics, soilless culture, yellow cedar, coir, greenhouse

Humicola fuscoatra infects tomato roots, but is not pathogenic

In 1993, a serious epidemic of a tomato root disease resembling corky root rot occurred in commercial greenhouses throughout Canada. Pyrenochaeta lycopersici could not be isolated from diseased roots, but Humicola fuscoatra was commonly isolated. The objectives of our work were to determine if H. fuscoatra is able to infect roots of tomato and cause corky root rot symptoms. Humicola fuscoatra was found to infect the roots of tomato seedlings and older plants. We concluded that H. fuscoatra is not a pathogen of tomato, however, because infection of tomato roots with the fungus did not necessarily lead to development of corky root rot or any other disease symptoms. Populations of H. fuscoatra increased greatly in sterile water or sterile nutrient solution, which would help to explain why commercial greenhouse growers can find this fungus in recirculating nutrient solutions.

Temporal variations of starch and mass in greenhouse tomato leaves under CO2 enrichment

Edwards, D., Ehret, D. and Jolliffe, P. 2011. Temporal variations of starch and mass in greenhouse tomato leaves under CO2enrichment. Can. J. Plant Sci. 91: 167-177. A plant-based method of guiding CO2 dosing may improve the effectiveness of CO2 enrichment in commercial greenhouse tomato (Lycopersicon esculentum Mill) production. The temporal dynamics of two plant response indicators, leaf starch and leaf mass per unit area (LMA) were investigated in commercial and research greenhouses throughout day/night periods, as well as after the onset of CO2 enrichment. Both leaf starch and LMA tended to follow the diurnal profile of light but with 3 to 4 h of lag. The magnitude of the response, especially for starch, was affected by leaf position, CO2 enrichment and light. The highest starch contents were measured between 1400 and 1600 and the lowest levels occurred in the morning between sunrise and 1100. In many cases plants carried over substantial starch in upper leaves from one day to the next, indicating a carbon-surplus state. In the onset experiment leaf starch and LMA increased with 4 d of exposure to CO2 enrichment for mid and upper canopy leaves and continued to increase to the end of the monitoring period (7 d). Leaf starch contents and LMA are indicators of plant carbon status that show potential for guiding CO2 dosing.

Demonstration of nutrient concentration effects on pineapple sage with the aid of automated crop monitoring

Summary The yield and quality of pineapple sage (Salvia elegans Vahl.) grown in two substrates (sawdust and rockwool) and at two nutrient solution concentrations (electrical conductivities of 1.7 and 4 mS cm–1) were compared in each of two years. No consistent effects of substrate were observed on any of the parameters measured, including plant fresh mass, dry mass, leaf area, chlorophyll content or shelf life. Leaf/stem fresh and dry mass ratios were also largely unaffected by substrate. Electrical conductivity (EC), however, had significant effects on most of these parameters. High EC reduced plant size, with lower plant fresh and dry mass, leaf number and leaf area. However, plant quality was improved as demonstrated by increased leaf/stem fresh mass ratio. In addition, chlorophyll concentrations were higher in high EC-treated plants, and shelf life was improved as shown by a reduction in percent water loss in cold storage. Load cells placed beneath the plants were used to monitor and compare transpiration and 24 h growth of high and low EC-treated plants grown in rockwool over a 90 d period. Daily growth recorded between 2400 and 0200 hours was found to be higher in the low EC-treated plants, supporting the observation of greater harvested fresh mass for those plants. Daily transpiration was found to be higher in the low EC plants, due mostly to their greater leaf area compared with high EC plants. When transpiration was compared on a leaf-area basis, no consistent differences were observed between EC treatments. Adapting the principles of a water-balance lysimeter, load cells were also found to be a useful means to check for relative moisture content of the substrate. Since transpiration and water replenishment (supply minus leachate) could be recorded independently, comparison of the two indicates an increase (replenishment > transpiration), decrease (replenishment < transpiration) or no change (replenishment = transpiration) in water content.