Martine Dorais

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.

Annual greenhouse tomato production under a sequential intercropping system using supplemental light

Abstract Greenhouse tomato plants ( Lycopersicon esculentum Mill. cultivar ‘Caruso’) were grown in a sequential cropping system, intercropping the young plants between the mature plants. The four trans-planting dates were 24 July, 2 November, 5 February and 19 April. The plants were cultivated on rockwool slabs and trained in a V-shaped system. The treatments were two levels of photosynthetic photon flux density (PPFD), 100 and 150 μmol m −2 s −1 , supplied by 400-W high-pressure sodium (HPS) lamps during a 16-h photoperiod from September to May, and three plant densities: (a) low density, 2.3 plants m −2 for all four successions; (b) variable density, 3.5/2.3/3.5/3.5 plants m −2 ; (c) high density, 3.5 plants m −2 for all four successions. The highest cumulative yields for the four successions (39 weeks picking) were 56 and 72 kg m −2 at 100 and 150 μmol m −2 s −1 , respectively, for the variable planting density. Yields were respectively 14 and 34% greater at the high and variable densities than at the low density for the two light treatments. The higher PPFD treatment raised the total number of fruits picked by 10, 16 and 14% for the low, variable and high planting densities, respectively. With well-synchronized crops, at high-density plantings with supplemental lighting of 100 and 150 μmol m −2 s −1 , annual yields of 70 and 84 kg m −2 , respectively, are predicted.

UPTAKE AND TRANSLOCATION OF SULPHATE IN TOMATO SEEDLINGS IN RELATION TO SULPHATE SUPPLY

ABSTRACT Uptake and translocation of 35SO4 2− sulfate in intact tomato seedlings (Lycopersicon esculentum cv. Solairo) incubated in nutrient solutions containing four concentrations of sulfate were investigated. The 35S fractions were measured in roots, stem, old leaves, and young leaves over a 24-hour period. At deficient and excessive sulfate levels, the instantaneous sulfate uptake (Φoc) in tomato seedlings was strongly influenced by the sulfate concentration in the rhizosphere. Increasing the sulfate concentration in the rhizosphere from 0.1 to 10.4 mM resulted in a proportional increase in net uptake into the whole seedling. The transport of sulfate from root to shoot (Φcx) was almost the same in seedlings incubated at both 20.8 mM sulfate and 10.4 mM sulfate. Young tomato plants can regulate sulfate influx from the cytoplasm to the xylem and the net uptake. The highest influx of SO4 2− from the external solution to the cytoplasm (Φoc) and the highest efflux (Φco) was observed at the highest sulfate concentrations (20.8 mM), indicating extensive recycling at the plasma membrane. Our results suggest for the greenhouse tomato a sulfate concentration of 10.4 mM in the nutrient solution, which allowed an optimum uptake. The data provided further information on the events associated with sulfur redistribution.

Vulnerability of low temperature induced needle retention in balsam fir (Abies balsamea L.) to vapor pressure deficits

Low temperature (LT) exposure has been shown to delay postharvest needle abscission and senescence (NAS) in balsam fir and changes in vapor pressure deficit (VPD) are expected to alter these processes. Two and half year-old seedlings were exposed to a LT of 5°C for 15 days while the control (CT) group was maintained at 22°C. Seedlings were then exposed to four different VPD (0.22, 0.87, 1.3 and 1.86 kPa) and observed for relative water content (RWC), xylem pressure potential (XPP), membrane injury index (MII), stem capacitance (SC) and NAS. An interactive effect of LT and VPD was observed in RWC, XPP, MII and NAS. Low VPD (0.22 and 0.87 kPa) resulted in less negative XPP, lower electrolyte leakage, higher SC and ultimately higher NAS than those at high VPD. Maximum NAS was recorded at 0.22 kPa. At 1.86 kPa, LT had 5× lower RWC (13%), 3× more negative XPP (−1.1 MPa), 1.8× higher membrane damage and 35% lower NAS (47 days) than CT. The SC declined with an increase in VPD with no effect of LT. The XPP and RWC of LT seedlings showed a positive relationship with NAS with R2 values of 0.54 and 0.59, respectively. LT offered no benefits to NAS at high VPD environments.

Silicon Transporters and Effects of Silicon Amendments in Strawberry under High Tunnel and Field Conditions

Together with longer production periods, the commercial transition to day-neutral strawberry (Fragaria × ananassa) varieties has favored the development of diseases such as powdery mildew (Podosphaera aphanis) that thrives in late summer-early fall. In an attempt to find alternative solutions to fungicides currently employed to curb the disease, we wanted to investigate the potential of silicon (Si) amendments that have been associated with prophylactic properties against powdery mildews. To this end, our first objective was to determine if strawberry was a Si-competent species following the recent characterization of the properties of Si transporters that plants must carry to uptake silicic acid. Based on genomic data, we were able to conclude that strawberry contained both functional influx (Lsi1) and efflux (Lsi2) transporters for Si uptake. Subsequently commercial experiments under high tunnel and field conditions were conducted with different Si fertilization regimes: constant soluble Si feeding in high tunnel, and bi-weekly soluble Si feeding or three concentrations of calcium silicate fertilization in the field. Results from high tunnel experiments showed that strawberry could accumulate as much as 3% Si on a dry-weight basis, the highest concentration ever reported for this species. All six tested cultivars contained roughly the same concentration, thereby confirming the limited genetic variability, also observed in other species, associated with the trait. Silicon fertilization under high tunnel led to a significant reduction of powdery mildew severity in both years and on all cultivars, and a significant increase in yield of marketable fruits reaching as much as 300% with cv. Monterey. By contrast, Si fertilization under field conditions in soils deficient in plant available Si, either in soluble or solid form, did not result in significant accumulation of Si in plants, regardless of the cultivars, year or concentrations. Our results have thus provided both genotypic and phenotypic proof that strawberry can greatly benefit from Si fertilization, but have also highlighted the importance of validating the fertilization regime to ensure that Si is properly absorbed and/or available to the plant.