M.S. - Horticulture

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    Evaluation of 13 Rootstocks for 3 Sweet Omage Clones for Tolerance to Tristeza Virus at Malama-ki. Hawaii
    ( 1979) Zee, Francis Tso Ping
    Fifteen-year old 'Washington Navel', 'Valencia', 'Pera', and 'Ortanique' cultivars grafted on thirteen citrus rootstock species and hybrids were evaluated for tristeza tolerance at the University of Hawaii, Malama-Ki Experimental Farm. One hundred percent natural infestation of all experimental trees was detected and confirmed by use of Immunodiffusion test and the viral inclusion staining technique. Cultivars grafted on sour orange, 'Sampson' tangelo and Citrus amblycarpa rootstocks were lost due to tristeza prior to 1972. 'Batangas' and rough lemon were rootstocks that produced the most vigorous growth. 1978 seasonal production was high with trees on rough lemon, 'Batangas', 'Rangpur', 'Kona orange', 'Cleopatra' and Citrus sunki. Upright growth habit was observed with trees on 'Cleopatra' and 'Rangpur' rootstocks. The best quality fruit was harvested from trees grafted on Citrus sunki and 'Cleopatra' rootstocks. 'Heen naran' performed well with 'Washington Navel' but was not a satisfactory rootstock for the other three cultivars. In this experiment, Citrus taiwanica, 'Siamelo' and 'Troyer' were not desirable rootstocks due to poor production. Citrus amblycarpa, 'Sampson' tangelo and sour orange were not suitable rootstocks for oranges and mandarins because of their susceptibility to tristeza virus.
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    Pollination and Fruit Set of Acerola
    ( 1960) Yamane, George M.
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    Ethylene Biosynthesis, Perception, and Sinaling-Related Gene Expression During Papaya Fruit (Carica papaya L.) Ripening
    ( 2012) Wu, Ping-Fang
    A gaseous plant growth regulator, ethylene, plays an important role during plant growth and development and includes ethylene dependent fruit ripening. Fruit ripening is a series of biochemical, physiological and structural events that lead to maturity. Papaya (Carica papaya) is a typical climacteric fruit that which performs dramatic changes in color, texture, and flavor during fruit ripening. Fruit ripening process was considered highly related to the biosynthesis of ethylene which is mainly controlled by the SAM (S-Adenosyl methionine synthetase. Methionine adenosyltransferase), ACS (1- aminocyclopropane-l-carboxylic acid synthase), and ACO (1-aminocyclopropane-lcarboxylic acid oxidase) genes. In addition, the ethylene receptors in Arabidopsis and tomato have been shown to be involved in effecting fruit development and the timing of fruit ripening, respectively. Ethylene signaling transduction gene expressions, such as CTR (Constituted Triple Response), EIN2 (Ethylene Insensitivity 2), EIN3/EILs (Ethylene Insensitivity 3 and Ethylene Insensitivity 3- Like proteins) and ERF (Ethylene Response Factors) are also involved in the ripening processing. The full sequencing of the papaya genome, coupled with microarray technology, provides a chance to determine the expressions of genes at specific fruit developmental stages. Thirty-four genes involved in ethylene biosynthesis (SAM, ACS, ACO, and ETO), perception (ETR) and the signaling transduction pathway (RAN, CTR, EIN2, EIN3/EIL1, and ERF) were selected from 24,421 predicted genes in papaya genome. Four developmental stages: mature green, the 25% color, 80% color and 100 color stage were investigated. The ethylene biosynthesis genes seemed to be expressed before the initiation of fruit ripening, and declined once the System 2 ethylene production was started. The ethylene receptors have been shown to be involved in the regulation of tomato fruit ripening. Our results showed fewer number of ethylene receptors than in tomato and Arabidopsis and also showed a possible role in controlling the initiation of papaya fruit ripening. More genes related to the ethylene signaling transduction pathway did not change in expression level during fruit maturation and ripening, except for CTR and RAN. CTRl and RAN are considered as negative regulator in the signaling pathway and a copper transporter associated with ethylene receptor respectively. In papaya, changes in sugar content, production of flavor constituents and rapid pulp softening during ripening can affect the quality and cause serious postharvest losses during transportation and storage. Knowing the ethylene-related gene expression during papaya fruit development and ripening may be helpful in regulating the timing of ripening, in order to control the fruit quality and reduce the postharvest losses.
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    Atrazine Drift Studies with Horticultural Crops
    ( 1966) Wong, Melvin K.
    The feasibility of diagnosing atrazine drift accurately with physical symptoms and tissue analysis was studied extensively with cucumber plants. Concentrations of atrazine ranging from 0.0005 to 1.0 lb. active/A were sprayed on mature cucumber plants. Although the physical symptoms resembled many other types of damage, the symptoms were sufficiently distinct to be used as secondary evidence along with tissue analyses. Physical symptoms appeared initially 2 or 3 days after the spraying as marginal and/or intervenal chlorosis. These chlorotic symptoms turned briefly to a bleached-white color on the leaves, which became necrotic within 5 days after spraying. The H. S.P.A. Method, an ultraviolet spectrophotometrlc method, was evaluated and found suitable to detect the presence of atrazine in cucumber tissue at levels where physical symptoms were difficult to detect and essentially no damage occurred. Although the addition of alumina columns to the H.S.P.A. Method was not necessary with cucumber leaves under the test conditions, they were beneficial when snap beans were analyzed. Alumina columns decreased interfering background and were not responsible for any loss of atrazine. To determine the best time to sample, cucumber plots were sprayed with 0.1 lb. active/A atrazine and harvested 12 hours, 1, 2, 4 and 7 days after the spraying. The samples were analyzed using the H.S.P.A. Method. The sampling time experiment showed a rapid decrease of atrazine from the time of spraying to 4 days after the spraying and very little decrease of atrazine from 4 to 7 days. For consistency samples should be taken 4 to 7 days after the suspected drift even though an earlier sampling would give higher tissue readings. After 7 days the damaged leaves started to fall from the plant. In all field experiments the sampling of only the most damaged leaves proved to be a very satisfactory procedure.
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    Embryological Study of Reproductive Barriers in InterspecificCrosses Between Carica Papaya L. and C. Cauliflora Jacq.
    ( 1987) Wenslaff, Timothy Frank
    The nature of sexual incompatibility between C. papaya L. and C. cauliflora Jacq. was examined. Pollen tube fluorescent staining studies revealed no inhibition of pollen tube development. Serial sections of developing hybrid-crossed ovules revealed significant postzygotic abnormalities, with reciprocal hybrid differences. On C. papaya females pollinated by C. cauliflora, embryos aborted at a microscopic, undifferentiated stage beginning about the 45th day, normal endosperm was lacking, and intact pollen tubes persisted a shorter time than in intraspecific ovules. On C. cauliflora females pollinated by C. papaya, abortion was evident in some ovules by the 45th day, but in others polyembryony was observed, with differentiation ranging from none to fully differentiated. A minority of mature seeds yielded large, fully-formed multiple embryos; there appeared to be potential for ^ vitro germination. No endosperm was found. All embryos in both reciprocal hybrid crosses appeared to derive from the hybrid zygote, based on their orientation and location in the ovule.
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    Genetic Transformation of Papaya (Carica Papaya, L.) Cultivar Kapoho by Particle Bombardment
    ( 1996) Wang, Xiaohu
    Papaya transformation systems were developed by Fitch et al. (1991) at the University of Hawaii, and transgenic 'Sunset' papayas with papaya ringspot virus (PRV) coat protein (cp) gene showed complete resistance to papaya ringspot virus (PRV) in the field tests (Manshardt et al, 1994). In our studies, we transformed 'Kapoho' papaya, the major crop on the Big Island, Hawaii, based on Fitch’s (1991) papaya transformation systems, and obtained transgenic 'Kapoho' papaya plants. The coat protein (cp) gene of PRV, along with a kanamycin selective marker gene (neomycin phosphotransferase, NPTII) and a Pglucuronidase (GUS) reporter gene, were constructed into the same plasmid vector by our collaborators at Cornell University and transformed into papaya tissue by particle bombardment. Transgenic 'Kapoho' papaya plants were obtained following somatic embryogenesis from hypocotyl callus on kanamycin selective medium and showed GUS positive expression. Immature zygotic embryos were excised and bombarded with gold particles. Following different treatments of indole-3-butyric acid (IBA), chimeric hypocotyls were harvested on germination medium 20 days after bombardment. Somatic embryogenesis from sections of chimeric transgenic hypocotyls occurred on induction medium and the transgenic embryos were cultured on selective induction medium or maturation medium with different concentrations of kanamycin for eight months. Then, the embryos were regenerated on germination medium without kanamycin. GUS was assayed in all experimental steps, and different GUS positive results were observed at different developmental stages. ELISA assays of coat protein and NPTII in chimeric transgenic hypocotyls showed positive expression and a high efficiency of transformation.