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Smiljana Goreta, Lovre Bucan, Gvozden Dumicic, and Daniel I. Leskovar

Globe artichoke is a native crop of the Mediterranean region with about 80% worldwide production. It is estimated that about 3,000 ha are grown in the U.S., mostly in California. Artichoke crop can be grown as a perennial, by vegetative cuttings, or as annual by seeds. Crop production can be limited by freezing winter temperatures leading to irreversible plant damage or by high summer temperatures causing poor head quality. Successful artichokes production, particularly in areas with constraining climatic conditions, requires proper selection of cultivars and planting dates. Cultivars with low vernalization requirements are more prone to a short growing season. The application of GA3 to overcome the lack of low temperatures and fulfill the vernalization requirements of early cultivars is well known. The goal of this multi-year project is to select production strategies contributing to earliness, extension of harvesting period, and improved yield and head quality under a variety of environmental conditions in Croatia and Texas. Selecting cultivars with different maturity groups and planting dates enabled harvesting period from autumn to late spring depending on locations. When GA3 was applied (12.5 to 125 ppm) on a naturally vernalized crop from autumn planting, early yield was substantially increased without affecting earliness. Conversely, application of GA3 (30 or 45 ppm) on nonvernalized plants established during late spring or summer was necessary for fall harvest in the Croatian locations. Head quality evaluated as head weight and size, or crude protein and total fiber concentration, progressively decreased during late spring harvest in Texas. Shifting the harvesting period towards early spring may be essential for improving head quality and for increasing the market share. To achieve adequate yields, longer harvesting period, and superior head quality, it is necessary to develop and adjust cultural practices for the specific growing area.

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Smiljana Goreta, Daniel I. Leskovar, and John L. Jifon

Successful field establishment of vegetable transplants often depends on the ability of young seedlings to tolerate various biotic and abiotic stresses after transplanting. Treatments that limit transpirational water loss could improve plant survival and stand establishment. In this study we evaluated growth and physiological responses of pepper (Capsicum annuum L.) seedlings to foliar application of chemical plant regulators [abscisic acid (ABA) and aminoethoxyvinylglycine (AVG)] or physical film-forming barriers [AntiStress (AS), Transfilm (TF), and Vapor Gard (VG)] during transient 4-day water deficit cycles. During two 4-day water deficit cycles, stomatal conductance (g s) and net CO2 assimilation rate (ACO2) were unaffected by the application of physical materials, but differed for ABA and AVG. Compared with untreated control plants, ABA reduced g s (47% to 69%) and ACO2 (37% to 57%) by the end of the second water deficit cycle, whereas AVG increased gs (27% to 60%) during the first desiccation cycle. Leaf (ψlf) and stem (ψst) xylem water potential of plants treated with film-forming materials generally decreased at the same rate as those of untreated plants, whereas application of AVG caused earlier and more pronounced decline of ψlf. Application of ABA enabled the maintenance of ψlf and ψst during two desiccation cycles, and thus prevented an increase of electrolyte leakage and leaf abscission. Growth rates of all plant components were reduced after ABA applications. However, allometric relationships showed similar patterns of dry matter allocation in leaves and shoots among ABA, TF, VG, and untreated control plants. Application of AS reduced allocation of dry matter to leaves, whereas AVG enhanced it at the expense of roots. These data indicate that water deficit tolerance of pepper seedlings only occurred with foliar application of ABA. This effect was associated with improved plant water relations, increased cell membrane stability, reduced leaf abscission, and a transient reduction in plant growth rates.

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Daniel I. Leskovar, Virgil Esensee, and Helen Belefant-Miller

Spinach (Spinacia oleracea L.) seed germination can be inhibited by high temperatures. An understanding of thermoinhibition in spinach is critical in predicting germination and emergence events. The purpose of this study was 3-fold: 1) to determine seed germination percentage and rate of spinach genotypes—`Cascade', `ACX 5044', `Fall Green', and `ARK 88-354'—exposed to constant and alternating temperatures; 2) to determine the nature and extent of inhibition imposed by the pericarp; and 3) to investigate leachate and oligosaccharide involvement in thermoinhibition. Germination inhibition began at >20 °C constant temperature and was totally suppressed at 35 °C. Alternating temperatures at 30/15 °C (12-hour day/12-hour night) resulted in greater germination than a constant 30 °C. The genotype sensitivity to supraoptimal temperatures was in the order of `ARK 88-354' ≤ `Fall Green' < `ACX 5044' < `Cascade', but the highly thermoinhibited `Cascade' seeds retained the ability to germinate when shifted to lower incubation temperatures. The pericarp inhibited germination, since seeds deprived of the pericarp had ≈90% germination at 30 °C. `ACX 5044' and `Cascade' had higher ABA content in the pericarp than `ARK 88-354' and `Fall Green'. Before imbibition at 30 °C, raffinose levels in each genotype were in the order of `ARK 88-354' > `Fall Green' > `Cascade'. After 48 hours of imbibition, sucrose and glucose levels were highest and raffinose levels were lowest in `ARK 88-354' and `Fall Green' seeds, while `Cascade' seeds remained less active metabolically. These data suggest that the pericarp apparently acts as a physical barrier as well as a source of inhibitors during thermoinhibition.

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Daniel I. Leskovar, Smiljana Goreta, and Jose A. Franco

The aim of this study was to determine whether aminoethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, would affect earliness, increase yield, and improve overall at harvest and postharvest quality of melon (Cucumis melo L. group Cantalupensis, `Sol Real'). Field experiments were conducted during two seasons with AVG (124 g·ha–1 a.i.) applied as spray or soil injected into the root zone with a single or double application between 7 d and 21 d before harvest. The AVG soil injection method increased earliness compared with AVG spray in one season. Total marketable yield increased with AVG injection but not with the AVG spray method compared with the control. Regardless of method of application, AVG did not affect fruit firmness, rind thickness, netting, or soluble solids content when measured at harvest. However, AVG spray decreased fruit size and seed cavity in one season. Similarly, AVG spray did not affect fruit quality after storage, whereas AVG soil injection increased fruit firmness. Overall, melon yield and fruit quality responses to preharvest AVG applications were superior for the soil injection than the spray method.

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Daniel I. Leskovar, Shinsuke Agehara, Kilsun Yoo, and Nuria Pascual-Seva

Agricultural communities in the semiarid regions of the world are constantly being affected by water scarcity, increased regulations restricting water use, strong competition for irrigation water with the urban sector, and severe drought periods. Conversely, the consumer demand for high-quality and nutritious foods is increasing rapidly. A 2-year field study evaluated growth, yield, and bulb quality in response to precision planting density and deficit irrigation of onion (Allium cepa L.) in southwest Texas. Seeds of short-day sweet onion cv. Texas Grano 1015Y were planted in the field on 11 Nov. 2007 and 30 Oct. 2008 at two planting densities (PDs), 397,000 (standard) and 484,000 (high) seeds/ha. Three irrigation rates using growth stage-specific crop coefficients and subsurface drip were imposed after plants were fully established, 100%, 75%, and 50% crop evapotranspiration rates (ETc). Total rainfall plus irrigation received for each irrigation rate were 594, 501, and 413 mm in 2008 and 662, 574, and 486 mm in 2009. In both seasons, there were consistent trends in growth, yield, and quality parameters. Leaf fresh weight was unaffected by PD but was reduced by deficit irrigation at 50% ETc. Although increasing planting density reduced the average bulb size by 12%, it increased the number of marketable bulbs by 21% to 33% and marketable yield by 7% to 14%. In contrast, deficit irrigation showed a trend to reduce both the number of bulbs and bulb size with yield reductions of 8% to 13% at 75% ETc and 19% to 27% at 50% ETc. Neither planting density nor deficit irrigation rate had a significant effect on soluble solids content, pungency, or quercetin contents. These results suggest that growers of short-day onions in semiarid regions could adjust PDs to target high-value bulb sizes. Implementing water-conserving practices (deficit irrigation at 75% ETc rate) would result in a decrease of high-value bulb grades and modest losses in yield but not flavor or nutritional components.

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Kevin M. Crosby, Daniel I. Leskovar, and Kil Sun Yoo

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Kevin M. Crosby, Daniel I. Leskovar, and Kil Sun Yoo

At the Vegetable and Fruit Improvement Center, plant breeding has produced pepper lines with enhanced beneficial phytochemical levels. TAM `Dulcito' is a new jalapeño cultivar with no detectable levels of capsaicin, but increased levels of lutein. In greenhouse cultivation, it contained 122 ppm of this important human health-related compound, which aids in prevention of macular degeneration. This is a significant improvement over popular cultivars, such as `Grande', which contained 25 ppm or less. In addition to improved lutein levels, `Dulcito' also possesses resistance to three important potyviruses: TEV, PepMoV, and PVY. In field trials at Weslaco, Texas, `Dulcito' outyielded both TAM `Mild Jalapeño 2', and `Mitla'. This new cultivar produces a concentrated set of large, thick-fleshed fruit with few cuticular cracks. Because of its lack of pungency, it should be useful for the processing industry. TAM `Tropic Bell' is a medium-sized, blocky bell with enhanced levels of both ascorbic acid and lutein compared to other cultivars. Grown under greenhouse conditions, it contained 100 ppm lutein compared to 6 ppm in `Jupiter'. It also contained 660 ppm ascorbic acid at the green stage, compared to less than 100 ppm for three commercial bell cultivars tested. `Tropic Bell' produced yields equal to both `Valiant' and `Summer Sweet' commercial hybrids at Weslaco. Fruit of `Tropic Bell' were slightly smaller than the hybrid cultivars. TAM `Tropic Bell' possesses resistance to the same three potyviruses as `Dulcito' and demonstrated excellent tolerance to Phytophthora capsici in a controlled inoculation. These two new cultivars will be useful for production in locations with high potyvirus pressure or as specialty market items for health-conscious consumers.

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Daniel I. Leskovar, Larry A. Stein, and Frank J. Dainello

The objective of this work was to determine the effect of within-row plant spacing and mulching on growth, quality, and yield of an experimental semi-savoy spinach (Spinacea oleracea L.) genotype `Ark-310' to produce a high quality fresh market product. Within-row spacings were 15 and 25 cm, and mulching treatments were bare-soil and black polyethylene mulch. Plants were destructively sampled weekly (1995-96) or bi-weekly (1997-98) for leaf area (LA), leaf number, leaf dry weight (LDW) and root dry weight (RDW) measurements. Plants grown on plastic mulch at 25-cm spacing had greater LA, LDW, and RDW than when grown at 15-cm spacing on mulch or bare-soil. Leaf number and specific leaf area (LA/LDW) were less affected by either spacing or mulching. The amount of soil on harvested leaves was lower on plants grown on plastic mulch in both years. In one year, total yields (MT/ha-1) were 42% higher at 15-cm than at 25-cm plant spacing, while mulch increased yields by 20%, independently of plant spacing. These effects were not evident in the year with higher rainfall (1997-98).

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Haejeen Bang, Sunggil Kim, Daniel I. Leskovar, and Stephen King

Fruit color and carotenoid composition are important traits in watermelon. Watermelon fruit color inheritance has revealed that several genes are involved in color determination. Carotenoids are known to have various functions in plants and animals, such as providing antioxidant activity and other health benefits for humans, and UV protection and pigmentation for plants. Differential gene activity in the carotenoid biosynthetic pathway may result in different color determination of mature fruit. Eight genes encoding enzymes involved in the pathway were isolated and their structures were characterized. While obtaining full-length cDNA of these enzymes, two single-nucleotide polymorphisms were detected in a coding region of lycopene β-cyclase (LCYB). These SNP markers showed cosegregation with red and canary yellow fruit color based on the genotyping of two segregating populations. This will lead to development of a codominant molecular marker for the selection of LCYB allele, which may allow breeders to distinguish between red and canary yellow watermelon fruit colors at the seedling stage.

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Giovanni Piccinni, Jonghan Ko, Thomas Marek, and Daniel I. Leskovar

Weighing lysimeters are used to measure crop water use during the growing season. By relating the water use of a specific crop to a well-watered reference crop such as grass, crop coefficients (KC) can be developed to assist in predicting crop needs using meteorological data available from weather stations. This research was conducted to determine growth stage-specific KC and crop water use for onions (Allium cepa L.) and spinach (Spinacia oleracea L.) grown under south Texas conditions. Seven lysimeters, consisting of undisturbed 1.5 × 2.0 × 2.2-m deep soil monoliths, comprise the Texas AgriLife Research–Uvalde lysimeter facility. Six lysimeters, weighing ≈14 Mg, have been placed each in the middle of a 1-ha field beneath a linear low-energy precision application irrigation system. A seventh lysimeter was established to measure reference grass reference evapotranspiration. Daily water use for onion and spinach was measured at 5-min intervals. Crop water requirements, KC determination, and comparison with existing Food and Agricultural Organization (FAO) KC values were determined over a 2-year period for each crop. The KC values determined over the growing seasons varied from 0.2 to 1.3 for onion and 0.2 to 1.5 for spinach with some of the values in agreement with those from FAO. It is assumed that the application of growth stage-specific KC will assist in irrigation management and provide precise water applications for a region of interest.