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Rhuanito Soranz Ferrarezi and Donald S. Bailey

Basil (Ocimum sp.) is a fast-growing, high-value cash crop for aquaponics. Plant suitability evaluation in tropical conditions is critical to recommend new cultivars, increasing grower portfolio and minimizing the production risks associated with untested selections. Two trials were conducted to identify suitable basil cultivars for tropical outdoor aquaponics production using the University of the Virgin Islands (UVI) Commercial Aquaponics System in the U.S. Virgin islands. We evaluated five basil cultivars in Summer 2015 (Genovese, Lemon, Purple Ruffles, Red Rubin, and Spicy Globe), and seven cultivars in Fall 2015 (Cinnamon, Genovese, Lemon, Purple Ruffles, Red Rubin, Spicy Globe, and Thai). In both trials, 3-week-old seedlings were transplanted in net pots at a density of 1.5 plants/ft2 (16.15 plants/m2). The 6-inch portions and upper portions of the canopy were harvested as a salable product and the resultant material (leaves and stems) considered as total yield per square meter. In the summer, yield was higher in ‘Genovese’ (14.91 kg·m−2) and ‘Spicy Globe’ (13.99 kg·m−2); ‘Purple Ruffles’ resulted in the lowest yield (4.18 kg·m−2). Leaf anthocyanin was greater for the red cultivars Red Rubin [28.35 anthocyanin content index (ACI)] and Purple Ruffles (34.36 ACI) compared with the other cultivars. Chlorophyll content was the highest in ‘Genovese’ [48.59 chlorophyll content index (CCI)]. In the fall, ‘Cinnamon’ (6.60 kg·m−2), ‘Genovese’ (6.70 kg·m−2), and ‘Spicy Globe’ (6.35 kg·m−2) showed the highest yield and ‘Purple Ruffles’ the lowest (1.68 kg·m−2). Leaf anthocyanin differed in all cultivars, with the higher values in Purple Ruffles (80.5 ACI) and Red Rubin (36.5 ACI). Chlorophyll content was a response of plant growth and cultivar, with values increasing over time and ranging from 12.06 (Lemon) to 17.99 CCI (Cinnamon). Plant growth index (PGI) was higher than that of other cultivars in Genovese and Lemon on day 58 (summer), and higher in Cinnamon on day 87 (fall). Yield was greater during the summer, which was calculated from May to August, in comparison with the fall, calculated from September to November. Yield declined for the fourth harvest in the summer, indicating that growers may need to end production after the third harvest and replant the crop. The results of this experiment indicate that basil has potential as a specialty, short-season, and high-value crop in the UVI Commercial Aquaponics System. Of the cultivars tested, Genovese and Spicy Globe were the highest yielding cultivars within the environmental and geographical conditions of this study for two consecutive seasons (summer and fall).

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Rhuanito S. Ferrarezi, Stuart A. Weiss, Thomas C. Geiger and K. Paul Beamer

Snow pea (Pisum sativum var. saccharatum) and sugar snap pea (P. sativum var. macrocarpon) are high-value crops typically grown in temperate regions. Temperature is the main limiting factor to growing edible-pod peas in warmer U.S. states and territories. The objective was to evaluate edible-pod peas performance in tropical climates and to make cultivar recommendations to farmers in the U.S. Virgin Islands based on fruit yield. Trials were performed in two consecutive years (2014 and 2015), testing six cultivars of edible-pod peas: three snow pea (Little Sweetie, Mammoth Melting, and Oregon Giant) and three sugar snap pea (Super Sugar Snap, Cascadia, and Sugar Sprint) in a complete randomized block with four replications. ‘Little Sweetie’ produced the highest total fruit yield for the season (15,442 kg·ha−1) and ‘Mammoth Melting’ (4249 kg·ha−1) and ‘Sugar Sprint’ (3349 kg·ha−1) produced the lowest total fruit yield in Year 1. The same trend happened in Year 2, where ‘Little Sweetie’ (14,322 kg·ha−1) and ‘Super Sugar Snap’ (12,511 kg·ha−1) were higher yielding and ‘Mammoth Melting’ (4582 kg·ha−1) and ‘Sugar Sprint’ (1929 kg·ha−1) were the lowest yielding cultivars. ‘Mammoth Melting’ showed a marketable yield below 80% of total yield in Years 1 and 2. ‘Mammoth Melting’ and ‘Super Sugar Snap’ produced the tallest plants in Year 1, while ‘Mammoth Melting’ was significantly taller than the others in Year 2. As expected, sugar snap pea presented fruit soluble solids concentration (SSC) 2.7% to 6.5% higher than snow pea. The snow pea cultivars had longer mean fruit length (81 to 86 mm) than sugar snap pea (60 to 68 mm). The opposite trend occurred with fruit thickness; sugar snap pea averaged 28.5% thicker than snow pea. The shoot dry weight of ‘Sugar Sprint’ was on average 78.5% smaller than ‘Mammoth Melting’ and ‘Oregon Giant’, resulting in poor performance due to small plant size. ‘Mammoth Melting’ and ‘Super Sugar Snap’ had the lowest chlorophyll content compared with the other cultivars. Results of this experiment indicate that edible-pod peas have potential as a specialty, short-season, high-value crop when grown in the cool–dry winter months of the U.S. Virgin Islands. Of the cultivars tested, Little Sweetie was the highest yielding cultivar evaluated within the environmental and geographical conditions of this study for two consecutive years.

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Marc W. van Iersel, Geoffrey Weaver, Michael T. Martin, Rhuanito S. Ferrarezi, Erico Mattos and Mark Haidekker

Photosynthetic lighting is one of the main costs of running controlled environment agriculture facilities. To optimize photosynthetic lighting, it is important to understand how plants use the provided light. When photosynthetic pigments absorb photons, the energy from those photons is used to drive the light reactions of photosynthesis, thermally dissipated, or re-emitted by chlorophyll as fluorescence. Chlorophyll fluorescence measurements can be used to determine the quantum yield of photosystem II (ΦPSII) and nonphotochemical quenching (NPQ), which is indicative of the amount of absorbed light energy that is dissipated as heat. Our objective was to develop and test a biofeedback system that allows for the control of photosynthetic photon flux density (PPFD) based on the physiological performance of the plants. To do so, we used a chlorophyll fluorometer to measure ΦPSII, and used these data and PPFD to calculate the electron transport rate (ETR) through PSII. A datalogger then adjusted the duty cycle of the light-emitting diodes (LEDs) based on the ratio of the measured ETR to a predefined target ETR (ETRT). The biofeedback system was able to maintain ETRs of 70 or 100 µmol·m−2·s−1 over 16-hour periods in experiments conducted with lettuce (Lactuca sativa). With an ETRT of 70 µmol·m−2·s−1, ΦPSII was stable throughout the 16 hour and no appreciable changes in PPFD were needed. At an ETRT of 100 µmol·m−2·s−1, ΦPSII gradually decreased from 0.612 to 0.582. To maintain ETR at 100 µmol·m−2·s−1, PPFD had to be increased from 389 to 409 µmol·m−2·s−1, resulting in a gradual decrease of ΦPSII and an increase in NPQ. The ability of the biofeedback system to achieve a range of different ETRs within a single day was tested using lettuce, sweetpotato (Ipomoea batatas), and pothos (Epipremnum aureum). As the ETRT was gradually increased, the PPFD required to achieve that ETR also increased, whereas ΦPSII decreased. Surprisingly, a subsequent decrease in ETRT, and in the PPFD required to achieve that ETR, resulted in only a small increase in ΦPSII. This indicates that ΦPSII was reduced because of photoinhibition. Our results show that the biofeedback system is able to maintain a wide range of ETRs, while it also is capable of distinguishing between NPQ and photoinhibition as causes for decreases in ΦPSII.

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Rhuanito S. Ferrarezi, Alan L. Wright, Brian J. Boman, Arnold W. Schumann, Fred G. Gmitter and Jude W. Grosser

Completely enclosed screen houses can physically exclude contact between the asian citrus psyllid [ACP (Diaphorina citri)] and young, healthy citrus (Citrus sp.) trees and prevent huanglongbing (HLB) disease development. The current study investigated the use of antipsyllid screen houses on plant growth and physiological parameters of young ‘Ray Ruby’ grapefruit (Citrus ×paradisi) trees. We tested two coverings [enclosed screen house and open-air (control)] and two planting systems (in-ground and container-grown), with four replications arranged in a split-plot experimental design. Trees grown inside screen houses developed larger canopy surface area, canopy surface area water use efficiency (CWUE), leaf area index (LAI) and LAI water use efficiency (LAIWUE) relative to trees grown in open-air plots (P < 0.01). Leaf water transpiration increased and leaf vapor pressure deficit (VPD) decreased in trees grown inside screen houses compared with trees grown in the open-air plots. CWUE was negatively related to leaf VPD (P < 0.01). Monthly leaf nitrogen concentration was consistently greater in container-grown trees in the open-air compared with trees grown in-ground and inside the screen houses. However, trees grown in-ground and inside the screen houses did not experience any severe leaf N deficiencies and were the largest trees, presenting the highest canopy surface area and LAI at the end of the study. The screen houses described here provided a better growing environment for in-ground grapefruit because the protective structures accelerated young tree growth compared with open-air plantings while protecting trees from HLB infection.

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Rhuanito S. Ferrarezi, Alan L. Wright, Brian J. Boman, Arnold W. Schumann, Fred G. Gmitter and Jude W. Grosser

Huanglongbing (HLB) disease is a threat to most citrus (Citrus sp.) producing areas and is associated with the bacterium Candidatus Liberibacter asiaticus. The disease is transmitted by the vector asian citrus psyllid [ACP (Diaphoria citri)]. Antipsyllid screen houses can potentially reduce and eliminate HLB development in young citrus plantings by excluding the insect vector. These structures are also anticipated to represent a new environmental platform to cultivate high-valued fresh citrus. The purpose of this investigation was to evaluate the effect of screen houses on excluding infective ACP from inoculating grapefruit (Citrus ×paradisi) trees and determine changes on environmental conditions caused by the screen cloth. We tested two coverings [enclosed screen house and open-air (control)] and two planting systems (in-ground and container-grown), with four replications arranged in a split-plot experimental design. Psyllid counting and HLB diagnosis were performed monthly, and the antipsyllid screen excluded the HLB vector from the houses. ACP and HLB-positive trees were found only at the open-air plots. Weather monitoring was performed every 30 minutes from 22 Feb. to 31 July 2014. Solar radiation accumulation averaged 6.7 W·m−2·minute−1 inside the screen houses and 8.6 W·m−2·minute−1 in the open-air. Air temperature was greater inside the screen houses whereas wind gusts were higher in the open-air. Reference evapotranspiration accumulation averaged 3.2 mm·day−1 inside the screen houses and 4.2 mm·day−1 in the open-air. There was no difference in cumulative rainfall between screen houses and open-air. The antipsyllid screen houses reduced solar radiation, maximum wind gust, and reference evapotranspiration (ETo). The environmental conditions inside the protective screen houses are suitable for grapefruit production.