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A. Rodríguez-Burruezo, J. Prohens, and F. Nuez

Twenty-six clones of pepino (Solanum muricatum Aiton) were evaluated for yield, fruit weight, fruit shape (length to width ratio), soluble solids concentration (SSC), titratable acidity (TA), and ascorbic acid concentration (AAC) over two growing seasons: autumn-winter (AW) and spring-summer (SS). Significant differences were found for the effects of clone, season, and clon× season interaction for all traits, except in the case of season for fruit shape. Mean values for yield, SSC, and AAC were higher in the AW than in the SS season, while mean fruit weight and TA were lower. Many clones (13 in AW and six in SS) had a yield higher than 30 t·ha-1. Substantial genotypic variation was found for all traits studied except for SSC. Clones stable for all traits were detected over both seasons, except for SSC, where the differences between seasons were very high. The significant clone × season interaction for all traits indicates that selection of genotypes adapted specifically to either AW or SS seasons would maximize the response to selection. Broad sense heritabilities were highest for fruit shape and yield (>0.70), while SSC had the lowest values (0.39 in AW, 0.17 in SS, and almost 0 when considering both seasons combined). For the AW season, significant fruit weight-SSC and fruit weight-AAC genotypic correlations were detected; for the SS season the significant genotypic correlations were yield-SSC, fruit weight-TA, fruit shape-TA, and SSC-TA. Results suggest there are ample opportunities for improving several traits in this crop using intraspecific variation for adaptation to specific environments.

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Hardeep Singh, Bruce Dunn, Niels Maness, Lynn Brandenberger, Lynda Carrier, and Bizhen Hu

Tomato (Solanum lycopersicum L.) is one of the most extensively cultivated horticultural crops in the world. Factors such as yield, size, taste, and lycopene content are important criteria that may impact the selection of tomato cultivars for different production systems. The aim of the current study was to evaluate different slicer and cherry tomato cultivars for production under greenhouse and open field conditions. Three cultivars of slicer (BHN 964, Trust, and Geronimo) and cherry (BHN 268, Favorita, and Sakura) tomatoes were tested using randomized complete block design in 2019 and 2020. Results showed that the performance of tested cultivars differed under greenhouse verses open field conditions. Among cherry tomato cultivars in 2020, BHN 268 and Sakura produced significantly greater yield under open field conditions, while under greenhouse conditions yield of BHN 268 was the lowest. Similarly, cherry tomato fruit size from ‘BHN 268’ and ‘Sakura’ was also significantly greater than ‘Favorita’ under field conditions, whereas under greenhouse conditions, the fruit size of ‘Sakura’ was significantly greater than both ‘BHN 268’ and ‘Favorita’. Among slicer tomato cultivars, BHN 964 produced significantly greater yield and had a greater average fruit size than the other two cultivars under greenhouse conditions in 2020 while, Geronimo produced significantly similar or larger yield and had a similar average fruit size compared with BHN 964 under open field conditions. Tomatoes produced under open field conditions were rated significantly greater for taste compared with those produced under greenhouse conditions. Lycopene content in both slicer and cherry tomato cultivars was influenced by the interaction of production type, cultivars, and harvest time. Therefore, it can be concluded that BHN 964 and Geronimo were the highest in lycopene among slicer tomato cultivars for greenhouse and open field production, respectively. Among cherry tomato cultivars, BHN 268 was the highest in lycopene for open field production and Sakura for greenhouse production. Additionally, open field–produced tomatoes taste better than greenhouse-produced tomatoes, but lycopene content may be constrained for mid- and late-season fruits due to high temperature conditions under open field conditions.

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Kent E. Cushman and Theodore W. Tibbitts

Chlorosis and necrotic spotting develop on the foliage of particular cultivars of potato (Solanum tuberosum L.) when grown under constant light. `Kennebec', a cultivar severely injured by constant light when propagated from tissue-cultured plantlets, also was injured when plants were propagated from small tuber pieces (≈1 g). However, plants did not develop injury when propagated from large tuber pieces (≈100 g). Plants from large tuber pieces grew more rapidly than plants from small tuber pieces. The role of plant vigor and carbohydrate translocation in controlling injury development is discussed.

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Brent Tisserat and Paul D. Galletta

Flowering and fruit production were obtained from cultured shoot tips of `California Wonder', `Super Cayenne', and `Zippy' peppers grown in a liquid Murashige and Skoog (MS) medium without growth regulators. Thirty-day-old pepper shoot tips, derived from seedlings germinated sterilely, were cultured in a 6-liter polycarbonate container coupled to an automated plant culture system (APCS). Plants were given ten daily, 30-minute, compressed-air applications at 300 ml/minute. These shoots began flowering after an additional 60 to 90 days in culture and flowered continuously thereafter. About 5% to 10% of the flowers set fruit. Maximum fruit size obtained was ≈25% to 75% of the size of fruit produced on plants grown in vivo. In contrast, no flowering occurred from shoot tips grown in 25 × 150-mm culture tubes containing agar medium and subcultured every 8 weeks to fresh medium. Immature fruit excised from plantlets grown in the APCS were cultured separately on agar medium containing 0.0, 0.1, 0.3, or 1.0 mg BA/liter with and without 0.1 mg NAA/liter. Isolated fruit grew best on MS medium with BA only and poorest on medium without growth regulators. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine (BA); 1-naphthaleneacetic acid (NAA).

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Regina R. Melton and Robert J. Dufault

`Sunny' tomato (Lycopersicon esculentum Mill.) seedlings were pretransplant nutritionally conditioned (PNC) in 1988 and 1989 with factorial combinations of N from 100 to 300 mg·liter-1 and P from 10 to 70 mg·liter-1. In 1988, all conditioned seedlings were exposed to 12 hours of 2C for eight consecutive nights before transplanting. In 1989, half of the conditioned plants were exposed to a low-temperature treatment of 8 days with 12-hour nights at 2C and 12-hour days in a warm greenhouse (19C/26C, night/day). In both years, as N PNC increased to 200 mg·liter-1, seedling growth increased. Increasing P PNC from 10 to 40 mg·liter-1 increased seedling growth, but only in 1988. In both years, P PNC did not affect yields. Low-temperature exposure in 1989 decreased seedling growth in comparison to those held in a warm greenhouse (19C/26C, day/night). In 1988, first harvest yields were not affected by N PNC; however, in 1989, as N increased to 200 mg·liter-1, early yields increased. In 1988, total yields increased wit h N PNC from 100 to 200 mg·liter-1 and in 1989 with N at 50 to 100 mg·liter-1 with no further increases from 100 to 200 mg·liter-1. Low-temperature exposure had no effect on earliness, yield, or quality. A PNC regime combining at least 200 mg N/liter and up to 10 mg P/liter should be used to nutritionally condition `Sunny' tomato seedlings to enhance yield.

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Robert J. Dufault and Jonathan R. Schultheis

To reduce transplant shock of bell peppers (Capsicum annuum L.), we tested the effectiveness of pretransplant nutritional conditioning (PNC) as a promoter of earliness and yield. In Expt. 1, `Gatorbelle' bell pepper seedlings were fertilized with N from Ca(NO3)2 at 25, 75, or 225 mg·liter-1 and P from Ca(H2PO4)2 at 5, 15, or 45 mg·liter-1. Nitrogen interacted with P, affecting shoot fresh and dry weight, leaf area, root dry weight, seedling height, and leaf count. In Expt. 2, transplants conditioned with N from 50, 100, and 200 mg·liter-1 and P at 15, 30, and 60 mg·liter-1 were field-planted in Charleston, S.C., and Clinton, N.C. Nitrogen- and P-PNC did not greatly affect recovery from transplant shock. Although N- and P-PNC affected seedling growth in the greenhouse, earliness, total yield, and quality were similar in field studies among all PNC treatments at both locations. PNC with 50 mg N and 15 mg P/liter can be used with this variety and not have any long-term detrimental effects on yield and quality.

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Kent E. Chushman and Theodore W. Tibbitts

The role of tehylene in the development of constant-light injury of potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.) was investigated. In one study, silver thiosulfate (STS) was applied to the foliage of four potato cultivars growing under constant light. Leaf area and shoot dry mass of `Kennebec' and `Superior', cultivars normally injured by constant light, were greater (P<0.05) than those of control plantsgiven foliar applications of distilled water. Examination of STS-treated `Kennebec' leaflets revealed significantly less injury (necrotic spotting and reduced starch content) than the water-treated controls. `Norland' and `Denali', cultivars tolerant of constant light, exhibited no differences in growth between treatments. In a second study, injury (necrotic spotting and reduced starch content) was induced in leaflets of `Denali' when exposed to spray applications of 0.5 mmol·L-1 ethephon or air containing 0.5 to 0.8 μL·L-1 ethylene. In a third study, three genotypes of `Ailsa Craig' tomato were grown under constant light. Leaves of the normal `Ailsa Craig' exhibited epinasty, reduced chlorophyll concentration, and reduced starch content. Leaves of a mutant `Ailsa Craig', containing the Never ripe mutation, did not exhibit epinasty but exhibited the same amount of reduced chlorophyll concentration and starch content as normal plants. Leaves of a transgenic `Ailsa Craig', containing an antisense gene of 1-aminocyclopropane 1-carboxylate (ACC) oxidase, were epinastic, but chlorophyll concentration and starch content were greater than in leaves of normal and mutant plants. These results suggest that transgenic plants were more tolerant of constant light than the other genotypes. Evidence from these studies indicates that ethylene, combined with constant light, has an important role in the development of constant-light injury.

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Kent E. Cushman, Theodore W. Tibbitts, Thomas D. Sharkey, and Robert R. Wise

Expanding leaflets of young `Kennebec' potato plants (Solanum tuberosum L.) develop visible necrotic spotting after 8 to 9 days of constant light and constant temperature, but little is known about this disorder before the appearance of injury. Whole-leaf autoradiography and iodine staining of terminal leaflets (5 to 10 mm long at the beginning of the constant-light period) showed a normal pattern of CO2 assimilation and starch content over the entire leaflet surface after 5 days of constant light. However, small areas of tissue devoid of CO2 assimilation and starch content became apparent on day 6, and these areas expanded to encompass much of the leaflet's medial and basal regions by day 7. At this stage of leaf development, on day 7, leaflets had attained 50% of their final leaflet length and ceased importing photosynthates from other leaves. Electron micrographs of chloroplasts from the medial and basal regions of leaflets on day 7 revealed a loss of membrane integrity and a senescence-like appearance. At this time, and within these affected regions, scattered groups of necrotic palisade cells began to appear. These scattered groups soon expanded in size and distribution and became apparent as visible necrotic spots on the upper leaflet surface by day 8 or 9. Leaflets on plants grown under constant light hut alternating temperatures, an environment known to be noninjurious, did not exhibit visible spotting or tissue devoid of starch content. In addition, none of these injury symptoms developed in `Denali', a potato cultivar tolerant of constant light. Despite its occurrence in expanding leaf tissue, constant-light injury appears to be a senescence-like event that leads to the catastrophic loss of photosynthetic competence, starch content, and chloroplast membrane integrity, producing chlorosis and necrosis of leaves and eventually stunting the plant.

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Alan W. Meerow, Rick J. Schoellhorn, and Michael Kartuz

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Félix H. França and Ward M. Tingey

The influence of light level on the expression of resistance in Solanum berthaultii Hawkes (accessions PI 473331 and PI 473334) to the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), was studied by exposing plants to two levels of photosynthetically active radiation: 272 ± 37 μE/m2 per sec and 1025 ± 150 μE/m2 per sec. Over 26 days, shading generally reduced densities of type A and B glandular trichomes, volume of trichome exudate, and phenolic oxidation activity of type A trichomes. In both light regimes, larvae reared on S. tuberosum L. were heavier, developed more rapidly, and had greater survival than those reared on S. berthaultii. Similarly, females reared on S. tuberosum were heavier and produced 10- to 20-fold more egg masses and 68 to 472 times more eggs than those reared on S. berthaultii grown at the same light level. Light level did not affect larval weight, developmental time, survival, adult weight, or fecundity of CPB on either host plant species.