Tom Helmer

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.

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

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.

Fruit cuticular and agronomic characteristics of a lecer6 mutant of tomato

Summary The agronomic and physiological characteristics of fruit were compared between two lines of ‘Micro Tom’ tomato which differed in their fruit cuticle chemistry. A wild-type (WT) and a mutant line (lecer6) deficient in β-ketoacyl-CoenzymeA synthase (LeCER6), an enzyme involved in cuticular wax synthesis, were studied. The lecer6 line showed significantly lower levels of wax aliphatics and higher levels of terpenoids. Lecer6 fruit also had lower levels of cutin monomers than WT fruit. The agronomic characteristics of fruit from the mutant line were generally different from WT fruit. Osmotic values and dry weight percentages (% DW) were higher than in WT fruit. These findings can be explained by the higher water permeance of the lecer6 fruit cuticle, resulting in a higher rate of cuticular transpiration. Fruit from lecer6 plants were not as firm as WT fruit, which may also have resulted from excessive water loss through the cuticle. Higher rates of water loss in lecer6 fruit did not seem to be related to changes in cuticle thickness. The biomechanical properties of the cuticle also differed between the two tomato lines. Transient creep tests of isolated cuticles were used to generate stress-strain curves for the fruit cuticles of each line. At the immature (green) stage of development, cuticles of WT fruit were more elastic than those of lecer6 fruit, as shown by a lower elastic modulus. However, at the mature (red) stage of development, WT fruit cuticles had become more rigid, and no differences were apparent between the two lines. These data show that a single gene mutation for fruit cuticular wax synthesis has a pleiotropic effect on many important agronomic and physiological attributes.