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Robert E. Paull

There is a need to develop effective, non-damaging, non-polluting, non-carcinogenic procedures for insect disinfestation and disease control in fresh horticultural products. The loss of ethylene dibromide as a fumigant and the uncertainties of other fumigants, has meant that alternatives are needed. The most likely possibilities include irradiation, heat, cold and controlled atmospheres. Irradiation doses required for sterilization of insects cause only minor physiological changes, while controlled atmospheres appear to require longer periods of exposure than the postharvest life of most tropical fruit. The sensitivity of tropical commodities to temperatures less than 10°C makes cold treatments inappropriate for most tropical commodities. Heat treatments seem to be most promising. For papaya, the requirement is that the fruit core temperature reach 47.2°C, this can occasionally disrupt fruit ripening. The sensitivity to heat is modified by seasonal, variety and rate of heating factors. The sensitivity can be related to the heat shock response and the presence of heat shock proteins.

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Jingwei Dai and Robert E. Paull

The growth and development of Anthurium andraeanum Andre cv. Kaumana flower before and after emergence from the subtending leaf base was studied. Eighty days before emergence, the anthurium flower was =0.3 cm long, enclosed by two tightly rolled stipules at the base of the subtending leaf petiole. During the rapid elongation stage of the leaf petiole, the flower (0.8 to 1.0 cm long) entered a period of slow growth 40 to 60 days before flower emergence. After the subtending leaf blade unfurled and had a positive photosynthetic rate, flower growth resumed. Spathe color development started =28 days before emergence when the flower was =50% of the emergence flower length (4.5 cm). At flower emergence, the spathe, excluding the lobes, was =75% red. The lobes did not develop full redness until 7 to 10 days after emergence. Peduncle growth was sigmoidal with the maximum growth rate 21 days after emergence. Spathe growth is characterized by a double sigmoid curve. The young, growing, subtending leaf blade had a negative net photosynthetic rate. Removal of this leaf blade advanced flower emergence by 18 days. The soft green leaf (25 to 30 days after leaf emergence) had a slightly positive measured net photosynthetic rate, and the removal of this leaf resulted in flower emergence 11 days earlier. A mature subtending leaf had the highest measured net photosynthetic rate, and its removal had little effect on flower emergence. The subtending leaf acted as a source of nutrients required for the developing flower. Altering the source-sink relationship by leaf removal accelerated flower emergence, probably by reducing the slow growth phase of the flower.

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Teeranuch Jaroenkit and Robert E. Paull

Heliconia (Heliconia spp.), red ginger (Alpinia purpurata), and bird-of-paradise (Strelitzia reginae) inflorescences have similar stem structures and postharvest handling regimes. Inflorescences, especially heliconia, should be harvested in the morning while still turgid, and at the most suitable stage of development which varies with the species, its proposed use, and market requirements. Treatments that extend postharvest vase life, either or both enhance water uptake or prevent water loss and provide an exogenous energy source. Use of the most suitable temperature for shipping and storage prolongs vase life. Heliconia should be shipped and stored at >10 °C (50.0 °F), red ginger >12 °C (53.6 °F), and bird-of-paradise at >8 °C (46.4 °F). Sucrose (10% w/v), citric acid [150 mg·L-1 (ppm)] and 8-hydroxyquinoline citrate (250 mg·L-1) are major chemicals used in pulsing and holding solution for bird-of-paradise. Holding solutions for red ginger are similar except 2% (w/v) sucrose is recommended. The response of heliconia inflorescences to different pulsing and holding solutions has been shown to be negligible. A 200-mg·L-1 benzyladenine spray extends the vase life of red ginger and heliconia. Hot water treatment of red ginger at 49 °C (120.2 °F) and 50 °C (122.0 °F) for 12 to 15 min extends postharvest vase life, kills most of the pests that infest red ginger, and reduces the geotropic response. The major postharvest problems are saprophytic mold on bird-of-paradise, negative geotropic response of red ginger, and insect infestation of all three flowers. There is no reported method to control the postharvest nectar and slime production on bird-of-paradise that provides a substrate for saprophytic mold growth. Dipping inflorescences in benomyl or thiobendazole (TBZ) at 200 mg·L-1 does help control postharvest mold growth in bird-of-paradise and heliconia. Compared to most temperate flowers, there is a need for greater understanding of morphological and physiological factors that limit the vase life of heliconia, red ginger and bird-of-paradise flowers.

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Yunxia Qiu and Robert E. Paull

Over ripe and abnormally soft fruits occur often during papaya shipments to the mainland U.S.A. Calcium fertilization to the soil did not always increased Ca concentration in the mesocarp. Calcium plus K treatment was more effective at increasing the Ca concentration in the mesocarp than Ca treatment alone. Calcium and K fertilization did not affect the fruit color development. There was a positive correlation between mesocarp Ca concentration and ripe fruit firmness, with no relationship between K or Mg concentration and ripe fruit firmness. Vacuum infiltration with CaCl2, MgCl2, KCl to mesocarp plugs in vitro showed that Ca significantly delayed softening and reduced C2H4 production, and that MgCl2 and KCl also slowed the softening. Use of the chelating agent sodium citrate increased the rate of softening, probably, by removing Ca from the cell wall. We conclude that Ca is an important factor in fruit firmness and that the increase of Mg and K by infiltration has different effects on fruit firmness from that by soil fertilization.

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Jingwei Dai and Robert E. Paull

The postharvest life of Dendrobium spp. flower sprays was limited by wilting and shedding of individual “flowers. Late-summer-harvested sprays had a reduced postharvest life compared to winter-harvested sprays. Cultivars differed in postharvest life in response to packing and storing for 2 days at 22C. Water 10ss rates of `Princess' sprays continuously held in deionized water declined from ≈ 1.25 g/day per spray 4 days after harvest to 0.35 g/day per spray 20 days later. Flower shedding occurred when the rate of water loss fell below ≈1.0 g/day per spray. Addition of a floral preservative to the vase water slowed the decline in water loss and increased postharvest life. Sprays packed and stored for 6 days at 22C had half the postharvest life of nonpacked controls held in deionized water or of sprays packed for 2 or 4 days at 22C. Submerging sprays in water immediately after harvest did not significantly increase postharvest life; submerging the sprays after harvest, before packing, and again after unpacking reduced postharvest life. Sprays could not be held for more than 4 days at 10C without suffering chilling injury. Silver thiosulphate (2 mm) and other silver preparations had no effect on postharvest life, although silver ions did reach the top flowers of the spray; thus, ethylene may play only a minor role in spray postharvest life. The postharvest life of sprays was increased by using boiled deionized water in vase solutions and by the continuous presence of chloramphenicol. Other antimicrobial agents, such as Physan, sodium hypochlorite, and sodium dichloro-s-triazinetrione dihydrate were without effect. Microbial growth in the vase solution and at the cut stem end mav have reduced water transport and induced subsequent flower wilting and shedding.

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Lili Zhou and Robert E. Paull

Papaya (Carica papaya L.) fruit flesh and seed growth, fruit respiration, sugar accumulation, and the activities of sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase (AI) were determined from anthesis for ≈150 days after anthesis (DAA), the full ripe stage. Sugar began to accumulate in the fruit flesh between 100 and 140 DAA, after seed maturation had occurred. SPS activity remained low throughout fruit development. The activity of SS was high 14 DAA and decreased to less than one-fourth within 56 DAA, then remained constant during the remainder of fruit development. AI activity was low in young fruit and began to increase 90 DAA and reached a peak more than 10-fold higher, 125 DAA, as sugar accumulated in the flesh. Results suggest that SS and AI are two major enzymes that may determine papaya fruit sink strength in the early and late fruit development phases, respectively. AI activity paralleled sugar accumulation and may be involved in phloem sugar unloading.

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Jingwei Dai and Robert E. Paull

The Anthurium andraeanum `Kaumana' flower growth and development before and after emergence was studied. The process before emergence was long and slow. A tiny flower bud, about 0.3 cm long was formed 80 days before its emergence. The whole period before emergence was divided into three phases: cell division phase, slow growth phase and elongation phase. The characteristic of each phase was studied.

The leaf which bears the flower bud at its petiole base is called subtending leaf. Its growth had a significant influence on the flower bud growth at its petiole base. Detaching the young subtending leaf blade resulted in an earlier flower emergence.

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Jingwei Dai and Robert E. Paull

The inflorescence of Protea neriifolia B. Br. was two-thirds of the total cut floral stem fresh weight and significantly influenced blackening of the attached 20 to 30 leaves. Floral stems harvested at five developmental stages were characterized for inflorescence diameter, fresh and dry weights, respiration, and nectar production. Inflorescence diameter and fresh and dry weights increased from stage 1 (very tight bud) to stage 5 (bracts reflexed). Respiration rate was high in stages 1 and 3. Nectar production began at stage 4 (open, cylindrical flower) and increased from 2.7 to 9.8 ml per flower with 15% to 23.5% total soluble solids as the flower opened. Postharvest inflorescence diameter, respiration rate, and nectar production increased and leaf blackening decreased when floral stems were placed in 5% (w/v) sucrose solution. Application of 14C-sucrose to a leaf subtending the inflorescence lead to >50% of the radioactivity being found in the nectar within 24 hours. These data indicate that leaf blackening in protea is the result of depletion of carbohydrate by the inflorescence, and that this depletion is primarily due to the sugar demand for nectar production.

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Lili Zhou and Robert E. Paull

This study examined the relationship between the activity of fruit enzymes involved in metabolizing sucrose and sugar accumulation during fruit development, to clarify the role of these key enzymes in sugar accumulation in papaya fruit. Papaya fruit (Carica papaya L. cv. Sunset) were harvested from 14 to 140 days after anthesis (DAA). Fruit dry matter persent, total soluble solids (TSS), and sugar composition and the activity of enzymes: sucrose phosphate synthetase (SPS), sucrose synthetase (SS), and acid invertase were measured. `Sunset' papaya matured 140 days after anthesis during the Hawaii summer season and in about 180 days in cool season on the same plant. Fruit flesh dry matter persent, TSS, and total sugar did not significantly increase until 30 days before harvest. Sucrose synthetase was very high 2 weeks post-anthesis, then decreased to less than one-third in 42 to 56 DAA, then remained relatively low during the rest of fruit development. Seven to 14 days before fruit maturation, SS increased about 30% at the same time as sucrose accumulation in the fruit. Acid invertase activity was very low in the young fruit and increased more than 10-fold 42 to 14 days before maturation. SPS activity remained very low throughout the fruit development and was about 40% higher in mature-green fruit. The potential roles of invertase and sucrose synthetase in sugar accumulation will be discussed.