Citrus and Horticultural Science

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This collection includes scholarly output from both faculty and students in Horticultural Science.


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Now showing 1 - 6 of 6
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    Controlled release fertilizer and soilless medium temperatures significantly interact during greenhouse production of Philodendron ‘Imperial Green’
    (International Society for Horticulture Science, 2022) Griffis Jr., J. L.; Manners, Malcom M.; Barnes, Q.
    Philodendron ‘Imperial Green’ is a commonly produced foliage plant in central Florida, but only general fertilizer recommendations for philodendrons are available to growers. Tissue-culture plugs of Philodendron ‘Imperial Green’ were potted up in green 15.24 cm pots using a standard peat/perlite soilless mix amended with dolomite and three rates of Diamond R 19-6-9 fertilizer blend also containing micronutrients and SureTRX, a proprietary amino acid additive. This controlled-release fertilizer (CRF) is formulated to release evenly over 180 days with soil temperatures of about 30°C. Soilless medium temperatures were measured continuously using Onset HOBO MX2202 Bluetooth Temperature/Light Data loggers buried in several pots. Plants were produced in the greenhouses under either full sun or 30% shade environments. Soilless medium temperatures were generally 1-2°C cooler in the shade during the day, but the temperatures dropped slowly after sunset such that there were no temperature differences between treatments at sunrise. The electrical conductivity (EC) for all pots was measured on a weekly basis using the standard pour-through method to evaluate the overall fertilizer levels available. The fertilizer was exhausted before 150 days in the plants growing in the full sun whereas the CRF lasted about the expected 180 days in the plants growing in 30% shade. Fertilizer stirred into the soilless medium was not affected by greenhouse light levels and all pots received the same automated irrigation treatments. Fertilizer release rates were closely related to the soilless medium temperatures. A small diurnal variation in soilless medium temperature had a considerable impact on fertilizer release rates over the full time of the experiment. Plants grown in full sun grew larger more quickly than plants produced in 30% shade for all fertilizer rates, but plants grown in 30% shade were a darker green color (as measured using a Nix Pro color sensor) for all fertilizer rates.
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    (International Society for Horticulure Science, 2015) Griffis Jr.,; McDonald, T. G.; Manners, Malcom M.; Bingham, J. P.
    Pitanga (Eugenia uniflora L.) has been produced on a small commercial scale in Hawai’i and Brazil for some years and the plants themselves are popular as ornamental hedges in both Southern Florida and many other places. Until recently, purple-fruited selections of pitanga have not been widely known or grown. It has been determined that purple pitanga fruits have substantially higher levels of certain desirable antioxidants than the common red-fruited types and that they generally have superior flavor as well. Unfortunately, the non-climacteric pitanga fruits should only be harvested at their visual and organoleptic optimum. They are highly perishable and have a short shelf life that limits marketability and potential expansion of demand. Because the pitanga has a long folk history in Brazil as a medicinal plant, considerable analysis has been performed on the effects of refrigeration on the organic constituents of the foliage. However, very little is known about the effects of postharvest refrigeration and storage on the physical or chemical qualities of the purple fruits. Our initial experiments with refrigerated storage of ripe, purple pitanga fruits in both Hawai’i and Florida lead us to believe that pitanga fruits may tolerate standard cold storage environment longer than expected and still retain market acceptability. Visual appearance, taste, moisture content and chemical constituents of purple fruits after varying periods of cold storage are all being evaluated. Changes in volatile chemical components during storage can substantially change the taste of the fresh fruits. Our selection and characterization of purple-fruited pitanga cultivars with high levels of desirable antioxidant, pleasing flavor profile and postharvest storability is in progress.
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    Advances in the purple-fruited pitanga (Eugenia uniflora) long-term breeding program in Hawai’I, USA
    (International Society for Horticulture Science, 2018) Griffis Jr., J. L.; McDonald, T. G.; Manners, Malcom M.; Tuncay, Ö.
    Pitanga is not a newly discovered fruit, although its commercial potential has not been widely developed. European explorers discovered the pitanga in South America several centuries ago and spread red-fruited seedlings throughout the tropics worldwide. However, only in Brazil has this crop seen significant commercialization of the fruits. In Hawai'i, fruits have long been popular in farmers' markets and they are in demand by processors and chefs. Interest in the crop has expanded rather recently because of the availability of purple-fruited, high-antioxidant, better-tasting fruits. Several purple-fruited selections were introduced to growers in Brazil in 2011. In Florida, the tasty 'Zill Dark' purple-fruited cultivar has been available for many years and one plant is the parent plant of the large seedling field of pitanga planted at the Kona Experiment Station in December 2006. Factors that have limited further development of pitanga include considerable variation among seedlings and their fruits, difficulty in clonal propagation, difficulty in harvesting the fruits and lack of recognizably superior cultivars. The planting at Kona, 137 seedlings from a 'Zill Dark' self-pollination and 20 grafted plants of 'Zill Dark' was utilized initially to develop fertilizer recommendations for interested local growers who might replace coffee with another crop. As the planting matured, it was evaluated for pest and disease problems and fruits from individual plants were evaluated for antioxidant content, flavor and postharvest quality. From September 2013 to September 2015, all individual plants were evaluated weekly for presence of flowers and/or fruits in various stages of development. Unlike Florida or Brazil, where both flowering and fruiting in pitanga are highly synchronized, the Kona field has fruits almost continuously year-round (although individual plants do go in and out of production). Analysis of the flower and fruit data collected has allowed comparison of the seedlings with the 'Zill Dark' grafted plants such that selections of early- and late-bearing seedling plants that extend the crop season substantially can be made. Some preliminary fruit yield data will allow us to select seedlings that may have higher yields than the 'Zill Dark' grafted plants. Fruit characteristics of promising seedlings will be evaluated for other important characteristics such as antioxidant content, fruit size and taste.
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    Unexpected variations in flowering and fruiting occur in clonally propagated, purple-fruited pitanga (Eugenia uniflora ‘Zill Dark’) grown in Kona, Hawai’i USA
    (International Society for Horticultural Science, 2018) Griffis Jr., J. L.; McDonald, T. G.; Tuncay, Ö.; Manners, Malcom M.
    Many tropical fruits such as the Brazilian purple-fruited pitanga (Eugenia uniflora) are not well known or widely produced outside of their countries of origin. The reasons many of these minor fruit crops do not become more widely available are complex. However, many of the reasons revolve around a lack of research into appropriate horticultural practices such as propagation, nutrition, pest and disease management, and proper harvesting, handling and processing. Another major missing component is cultivar improvement. The purple-fruited pitanga has several named selections available in Brazil, Israel and the USA, but difficulties with clonal propagation have severely limited their availability. Breeding trials using the purple-fruited pitanga ‘Zill Dark’ were initiated in Florida and seedling fields were planted out for further evaluation in both Florida and Hawai’i where the crop is already known. Additionally, twenty veneer-grafted ‘Zill Dark’ pitanga were also planted in the Hawaiian field to provide production data and to serve as comparisons to the seedlings. Scionwood was all obtained from the same ‘Zill Dark’ plant and seedling rootstocks were all grown from seed produced by the same plant that provided the scionwood, as there are no clonal rootstocks available for pitanga. In 2013, five years after the planting of the veneer-grafted ‘Zill Dark’ pitanga, collection of flowering and fruit production data from both the grafted trees of ‘Zill Dark’ and the seedlings was initiated. As a rule, clonally propagated fruit trees of the same cultivar that are the same age, planted in the same field and fertilized, irrigated and pruned in the same manner are expected to produce similar fruiting and flowering results. However, in the Hawaiian field there were statistically significant differences in both times of flowering and ripening of fruit among the ‘Zill Dark’ clones. Why these clonally propagated fruit trees do not have well-synchronized production schedules is unclear; possible causes for this dissimilarity are examined.
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    Breeding, research and development of purple-fruited pitanga (Eugenia uniflora L.) as a commercial crop in Hawai'i, USA - 2007 to 2017
    (International Society of Horticultural Science (ISHS), 2020) Griffis Jr., J. L.; Manners, Malcom M. ; McDonald, T. G.
    In 2003, purple-fruited pitanga was one of only 12 tropical fruit crops selected from more than 200 prospective crops for development in Hawai’i by tropical fruit growers, processors and chefs. The most desirable seedlings were selected for further research, plants of these were propagated by grafting and one established, named cultivar, ‘Zill Dark’, was selected as the parent for a breeding project to look for variation within the crop. A planting of 137 seedlings from a self-cross of ‘Zill Dark’ was installed in a field at the Kona Experiment Station in Holualoa, Hawai’i in February 2007. While evaluating the seedling plants for various traits, they were also used in a trial to evaluate the effects of fertilizer rates on growth and development of the crop. In summer 2008, 20 grafted plants of ‘Zill Dark’ were added to the field for comparison with the seedlings. Seedling plants may begin to produce fruits only two years after planting in the field, but full production takes several years of growth and maintenance. Grafted plants often produce some fruit within a year of grafting. The fertilizer trial continued for several years and fruits were harvested and evaluated for traits such as color, size and taste. Fruits were successfully marketed at local farmers’ markets and to local chefs. After six years in the field, fruit production data was collected for all of the purple-fruited seedlings and the ‘Zill Dark’ grafted plants from 2013 to 2015. Surprisingly, plants were not all synchronized to produce fruits at the same time, so the potential to find new varieties from among the seedlings that could alter the growing season for producers in Hawai’i was noted. Substantial variations in fruit yield and length of fruiting period were also discovered. In 2017, during further evaluation of fruits in the field, three seedlings in the plot were discovered bearing large numbers of ripe, seedless fruits, something not previously reported for this crop. These plants have been propagated by veneer graft for further evaluation. Experiments to measure brix in relation to exact fruit color of ripening fruits (measured with a Nix Pro Color Sensor) have also been initiated to determine if fruits might be harvested and marketable sooner in the crop cycle so that fewer fruits are lost when very soft, fully ripe fruits abscise and drop from the plants.
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    Purple-fruited pitanga - Antioxidant levels and flavors of mature fruits vary considerably among closely related cultivars
    (International Society for Horticultural Science (ISHS), 2012) Griffis Jr., J. L.; Sams, S. E.; Manners, Malcom M.; McDonald, T. G.; Radovich, T. J.
    Pitanga (Eugenia uniflora L.) has been produced on a small scale in Brazil for many years, and several food items such as juices, jellies, candies and drinks as well as cosmetic products such as shampoos, soaps and perfumes are available in the Brazilian marketplace. Some frozen fruit pulp has been exported to Europe. Seeds of red-fruited pitanga have been widely distributed throughout the tropics, and the seedling plants can be found in many countries, although the fruit is scarcely cultivated as a commercial fruit crop outside of Brazil. There is a small fruit production industry in Hawai’i, and the plants are popular ornamental hedge plants in southern Florida and many other places. Until recently, purple-fruited selections of pitanga have not been widely known or grown. It has been determined that purple-fruited pitanga has substantially higher levels of certain antioxidants than the common red-fruited types. Our chemical analysis by HPLC of freeze-dried purple pitanga pulp for anthocyanin pigments and carotenoids as well as analysis of mineral nutrients by ICP-MS show that concentrations of these materials are quite variable and highly dependent upon cultivar and fruit maturity. For example, lycopene concentrations varied by a factor of 10, as did lutein; quercetin varied by a factor of 4 among purple fruits harvested at the same times from sibling plants grown side-by-side in Hawai’i. Purple fruits harvested from selected mature pitanga siblings planted in both Hawai’i and Florida had rather widely divergent flavor profiles, and both fruit size and actual fruit color at maturity were also quite variable. Chemical analysis of purple fruits of unknown heritage may not be representative of levels of antioxidants found in purple fruits harvested from specific cultivars. Our selection and characterization of purple-fruited pitanga cultivars with both high levels of desirable antioxidants and pleasing flavor profiles is in progress.