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G. Préstamo and P. Manzano

The various isozymes of peroxidase of a range of vegetables and kiwifruit were compared using sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by specific activity staining. Peroxidase isozymes were determined in potato (Solanum tuberosum L.), carrot (Daucus carota L.), tomato (Lycopersicon esculentum Mill.), kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson], cauliflower [Brassica oleracea (Botrytis group)], green beans (Phaseolus vulgaris L.), and horseradish (Armoracia rusticana Gaertn, Mey Scherb.). There was only one isozyme in cauliflower (70 kDa), two in kiwifruit (45-43 kDa), and a range of isozymes (120-36 kDa) in horseradish. Ascorbic acid inhibited peroxidase activity in the extracts.

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Georges T. Dodds and Pamela M. Ludford

Chilling-injury symptoms on the surface of eight cultivars or lines of tomato (Lycopersicon esculentum Mill.) fruit were mapped with respect to subtending locules. Mature-green (MG) fruit were chilled at SC for 10 to 25 days and then ripened to red ripe at 20C. Mature-green fruit showed a major portion of injury over subtending locules and on the stem end. The location of injury corresponded with the regions that were the last to ripen. The injuries of immature-green (IG) fruit treated in a similar manner were different from those of MG fruit both in appearance and in distribution.

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Bernard A. L. Nicoulaud and Arnold J. Bloom

Concentrations of up to 1.0 μm NiCl2 in a nutrient solution improved growth of tomato (Lycopersicon esculentum Mill. `T-5') seedlings that received foliar urea as their sole nitrogen source. Nickel in the nutrient solution decreased the amount of urea present in the shoots and increased the amount in the roots, although it had no significant effect upon leaf urease activity. These results indicate that a) the presence of nickel in the nutrient solution improves growth of plants receiving foliar urea and b) the effect of nickel was related more to increased urea translocation from shoot to root than to enhanced leaf urease activity.

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Mervyn C. D'Souza, Suman Singha, and Morris Ingle

Chromaticity values (L*, a*, b*) of tomato (Lycopersicon esculentum Mill. `Celebrity', `Early Pick', and `Mountain Delight') were measured using a Minolta CR-200b tristimulus colorimeter. Lycopene concentrations in acetone extracts of skin disks or pericarp plugs were measured spectrophometrically at 503 nm. The L* or a* value was related to lycopene concentration in all the cultivars; however, the ratio of (a*/b*) provided the best R for all cultivars (0.75). These relationships allow the use of a portable colorimeter for rapid, nondestructive estimation of tomato fruit lycopene concentrations in laboratory or in situ studies.

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Elizabeth A. Baldwin and Russell Pressey

Exopolygalacturonase (exo-PG) (EC 3.2.1.67) was investigated for ability to induce ethylene production in green cherry tomatoes (Lycopersicon esculentum Mill.). The fruit were vacuum-infiltrated with various levels of exo-PG from green tomato fruit, squash flower, or oak pollen and compared to boiled enzyme or salt controls for ethylene production. In all cases, fruit treated with active enzymes produced significantly higher levels of ethylene than did control fruit. The ethylene response was evident 2 hours after treatment and was transient in nature, returning to basal levels by 22 hours. The amount of ethylene produced did not appear to be influenced by the source of exo-PG.

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Alejandro Fierro, André Gosselin, and Nicolas Tremblay

The experiment was conducted to determine the effects of CO, enrichment (900 μl·liter-1, 8 hours/day) in combination with supplementary lighting of 100 μmol·s-1·m-2(16-h photoperiod) on tomato (Lycopersicon esculentum Mill.) and sweet pepper (Capsicum annuum L.) seedling growth in the greenhouse and subsequent yield in the field. Enrichment with CO2 and supplementary lighting for ≈ 3 weeks before transplanting increased accumulation of dry matter in shoots by ≈ 50% compared with the control, while root dry weight increased 49% for tomato and 6270 for pepper. Early yields increased by =1570 and 11% for tomato and pepper, respectively.

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Martin P.N. Gent and Vincent Malerba

The soil within a greenhouse was heated by blowing hot air from a forced-air heater through drainage pipes buried beneath raised beds. This warmed the soil from 50F (10C) to 68F (20C) after 1 week of heating in mid-March. Soil in unheated beds did not warm to this temperature until May. The yield of tomato (Lycopersicon esculentum Mill.) planted in heated beds was higher than in unheated beds by 16% over the season in 1992, and by 14% as of early July 1993. The weight fraction of highest-quality fruit also were 11% greater in 1993. This simple method of soil heating involved negligible additional expense

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T.J. Swiecki and J.D. MacDonald

Exposure of tomato plants (Lycopersicon esculentum Mill.) to salinity stress either before or after inoculation with Phytophthora parasitica increased root and crown rot severity relative to nonstressed controls. The synergy between salinity and P. parasitic was most pronounced on young (prebloom) plants and least pronounced on older (postbloom) plants. Salt stressed, inoculated plants had significantly reduced top weight, significantly more root necrosis, greater incidence of crown necrosis, and significantly greater mortality. Increased disease severity occurred even though experiments showed salinity reduced zoospore release arid motility of P. parasitic, suggesting that even low inoculum levels can result in severe root rot on young tomato plants in saline soils.

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Wade H. Elmer and Francis J. Ferrandino

Paper mulch and black plastic mulch were compared with no mulch on tomatoes (Lycopersicon esculentum Mill. `Better Boy' and `San Marzano') for incidence of blossom-end rot (BER) in the field during 1988–90. Early season (late July to late August) harvest had more BER than in later pickings. Black plastic mulch significantly increased early season BER in `Better Boy' relative to paper or no mulch. Late-season BER in `San Marzano' was decreased with paper or black plastic mulch relative to no mulch.

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Kim E. Tripp, William K. Kroen, Mary M. Peet, and Daniel H. Willits

Eight tomato (Lycopersicon esculentum) cultivars were grown for 16 weeks in greenhouses enriched for an average of 8.1 hours daily to 1000 μl CO /liter of air or in greenhouses maintained at ambient CO. Carbon dioxide enrichment significantly decreased the mean number of greenhouse whiteflies [Trialeurodes vaporariorum (Westward), Homoptera: Aleyrodidae] as measured by counts from commercial yellow sticky traps. The number of whiteflies present was negatively correlated with both seasonal foliar C: N ratio and percent C but positively correlated with percent N in the foliage. Thus, CO enrichment apparently alters plant composition in such a way as to reduce significantly the population growth of greenhouse whiteflies.