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  • Journal of the American Society for Horticultural Science x
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`Solo' papaya (Carica papaya L.) fruit removed at different points from a commercial packing house showed that skin injury due to mechanical damage increased as fruit moved through the handling system. The occurrence of “green islands” -areas of skin that remain green and sunken when the fruit was fully ripe-apparently were induced by mechanical injury. Skin injury was seen in fruit samples in contact with the sides of field bins, but not in fruit taken from the center of the bins. Bruise-free fruit at different stages of ripeness (5% to 50% yellow) were dropped from heights of 0 to 100 cm onto a smooth steel plate to simulate drops and injury incurred during commercial handling. No skin injury occurred, although riper fruit showed internal injury when dropped from higher than 75 cm. Fruit (10% to 15% yellow) dropped onto sandpaper from a height of 10 cm had skin injury symptoms similar to those seen on fruit from the commercial handling system. These results suggest that abrasion and puncture injury were more important than impact injury for papaya fruit. Heating fruit at 48C for ≈6 hours or until fruit core temperature (FCT) reached 47.5C aggravated the severity of skin injury. Delays in the application of heat treatment from dropping did not reduce the severity of skin injury significantly, except for fruit heated 24 hours after dropping. Waxing fruit alleviated the severity of skin injury, whether applied before or after the heat treatment. Skin injury to papaya was caused by abrasion and puncture damage-not impact-and increased during postharvest handling of the fruit. The injury was associated mainly with fruit hitting the walls of wooden bins-bin liners may reduce this injury.

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Mesocarp softening during papaya (Carica papaya L.) ripening was impaired by heating at 42C for 30 min followed by 49C for 70 min, with areas of the flesh failing to soften. Disruption of the softening process varied with stage of ripeness and harvest date. The respiratory climacteric and ethylene production were higher and occurred 2 days sooner in the injured fruit than in the noninjured fruit that had been exposed to 49C for only 30 min. Skin degreening and internal carotenoid synthesis were unaffected by the heat treatments. Exposure of ripening fruit to either 42C for 4 hr or 38 to 42C for 1 hr followed by 3 hr at 22C resulted in the development of thermotolerance to exposure to the otherwise injurious heat treatment of 49C for 70 min. Four stainable polypeptide bands increased and seven declined in single-dimensional acrylamide gels following incubation of fruit at the nondamaging temperature of 38C for 2 hr. Three polypeptides showed marked increases when polysomal RNA was translated. These polypeptides had apparent molecular weights of 17, 18, and 70 kDa. Proteins with molecular weights of 46, 54, and 63 kDa had slight increases after heat treatment. The levels of these polypeptides peaked 2 hr after heat treatment and declined within 24 hr. The amount of these polypeptides in the unheated control varied with the batch of fruit. The concentration of three translated polypeptides, with apparent molecular weights of 26, 37, and 46 kDa, declined. Other polypeptides continued to be translated during and after holding papayas for 2 hr at 38C.

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Abstract

Papaya (Carica papaya L.), a climacteric fruit, became progressively less susceptible to chilling injury as it ripened. Symptoms of chilling injury included skin scald, hard areas in the pulp around the vascular bundles, and water soaking of tissue. Mature green fruit were most sensitive to chilling and began showing injury after 10 days of storage at 2°C. Chilling injury symptoms began to occur after 20 days at 7.5°. Fruit that showed 60% yellowing could be kept at 2° for 17 days without developing injury. Preconditioning papaya fruit for 4 days at 12.5° before storage for 12 or 14 days at 20° reduced chilling sensitivity. The decrease in chilling sensitivity with preconditioning was associated with partial fruit ripening. Waxing and wrapping papaya with polyethylene reduced chilling injury, but the fruit had an off-flavor. Controlled atmospheres of low oxygen (1.5% to 5%) with or without high C 02 (2% or 10%) delayed ripening, but did not reduce chilling injury symptom development. Calcium treatment led to increased chilling injury of papaya fruit. Delaying storage until the fruit ripened decreased chilling susceptibility and increased storage life at chilling temperatures. Shipping 60% yellow fruit at 2° could provide a procedure for achieving fruit fly disinfestation. Differences in cultivar response to chilling injury were noted.

Open Access

Abstract

The occurrence of intra-ovarian ovaries in certain strains of Carica papaya L. is not uncommon. Approximately 150 hermaphroditic and 25 female ovaries from a hybrid progeny contained internal ovaries in stages of development ranging from thread-like appendages to round or elongated pistils of various sizes and shapes. A few were large enough to fill the entire seed cavity of the primary fruit and possessed their own cavities with non-viable seeds.

Internal ovaries originate either from stimulated growth of rudimentary pistillate structures extending from the central axis of the receptacle or from placentae in positions normally occupied by ovules. The placenta may be in its normal parietal position or a single strand may become free, extended from the base of the primary ovary and support a mal-shaped secondary ovary as well as ovules. The occurrence of internal ovaries supports theories proposed by other investigators on the evolution of floral morphology in the papaya.

Open Access

Four papaya (Carica papaya L.) cultivars were cultured aeroponically or in perlite to determine the magnitude, timing, and root locality of Fe reductase induced by Fe deficiency. Five soybean [Glycine max (L.) Merrill] lines with a known range of Fe-deficiency chlorosis scores were cultured in perlite for comparison. Speed of inducement of Fe reductase activity was determined in plants cultured without Fe for 0 to 17 days. Location of Fe reductase activity was determined by sectioning roots from the tip to 60 to 70 mm proximal to the root tip from plants cultured without Fe for 16 to 19 days. The Fe reductase system was induced in all papaya cultivars after 7 to 11 days without Fe, and activity increased through 17 days. Iron reductase activity in all papaya cultivars was comparable to the most tolerant soybean line. The zone of highest activity was the apical 10 mm of roots. These results indicate that papaya roots are highly efficient in induced Fe reductase activity. The highest activity in root tips underscores the importance of maintaining a healthy, continually growing root system with numerous growing points when culturing papaya in alkaline substrates.

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Abstract

Sexual changes in papaya (Carica papaya L.) from the normal hermaphroditic elongata flower toward femaleness by means of stamen carpellody are discussed in relation to the transition from the bisexual elongata flower toward maleness. A series of changes occurs that involves reduction in ovary size and shape, and in numbers of stigmatic rays, dorsal vascular bundles, carpels, and placenta. Placentation is normally parietal in papaya but there is evidence of ancestral axil placentation.

Open Access

Field-grown `Red Lady' papaya (Carica papaya L.) plants were used to measure foliar gas-exchange responses to rapid changes in irradiance levels to determine if papaya stomata are able to track simulated sun-to-cloud cover transitions. Natural sunlight and neutral shade cloth placed over the leaf were used to provide high photosynthetic photon flux (PPF) of about 2000 μmol·m-2·s-1 until leaves reached steady state within the cuvette, followed by three minutes with low PPF of about 325 μmol·m-2·s-1, and a return to PPF of about 2000 μmol·m-2·s-1. Net CO2 assimilation (A) declined from an initial 20 μmol·m-2·s-1 to about 9 μmol·m-2·s-1 within 20 seconds of initiating low PPF, and remained fairly stable for the duration of the three minutes of low PPF. Stomatal conductance (gs) declined within 60 seconds of initiating low PPF, from 385 to about 340 μmol·m-2·s-1 during the three minutes duration of low PPF. Following the return to high PPF, A rapidly increased to about 18 μmol·m-2·s-1, then gradually increased to the original value. After a lag of about 1 minute following the return to high PPF, gs began to increase and returned to the original value after three minutes. Container-grown `Tainung #1' papaya plants were used in a second study to determine the influence of mild drought stress on gas-exchange responses to rapid irradiance transitions. For drought-stressed plants, gs declined to a greater magnitude following the high-to-low PPF transition, and gs and A recovered more slowly following the transition from low-to-high PPF than for well-watered plants. Water use efficiency declined to a minimum immediately following the high-to-low PPF transition for both sets of plants, but recovered more rapidly for drought-stressed plants. These results indicate that papaya stomata are able to track rapid changes in irradiance, and mild drought stress enhances the tracking response.

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The influence of drought stress on leaf gas exchange and chlorophyll fluorescence characteristics of field-grown papaya (Carica papaya L.) plants was determined under a range of incident light fluxes and times of day. These data may aid in improving management systems for papaya production which minimize detrimental effects from suboptimal environmental conditions. Water was withheld from field-grown `Red Lady' plants in one study and `Tainung #2', `Red Lady', and `Sunrise' plants in a second study until soil matric potential was -60 to -70 kPa. Drought-stressed plants exhibited reduced net CO2 assimilation (ACO2 ) above light saturation, photosynthetic photon flux (PPF) at which light saturation for ACO2 occurred, and apparent quantum yield compared to well-watered plants. The light compensation point of drought-stressed plants was greater than that of well-watered plants. Leaf chlorophyll fluorescence characteristics were not influenced by drought stress. The daily pattern of leaf gas exchange was dependent on climatic conditions. For sunny days, ACO2 , stomatal conductance of water (gs), and water use efficiency of well-watered plants were maximal at mid-morning, declined during midday, and then partially recovered during late afternoon. In drought-stressed plants, leaf gas exchange was relatively constant after a brief early morning maximum. On overcast days, the responses of gas exchange variables in relation to time of day followed smooth bell-shaped patterns regardless of the level of drought stress. Combined with previously published data, these results indicate that the influence of drought stress on gas exchange is highly dependent on time of day, ambient sky conditions, plant size, and speed with which drought stress occurs.

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Papaya (Carica papaya L.) source size and sink strength were modified by a single defoliation or continual defoliation and fruit thinning. Fruit set, development, weight, total sugar (sum of sucrose, fructose, and glucose), sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase (AI) enzyme activities in response to defoliation and fruit thinning were determined. The effects of defoliation and fruit thinning varied with weather conditions, plant growth conditions, and cultivar. Removal of 75% of the leaves significantly reduced new flower production and fruit set, and decreased ripe fruit total soluble solids (TSS), while 50% defoliation did not reduce new fruit set or ripe fruit TSS. When every third leaf from the oldest leaf was not removed, the number of new flowers was reduced by 47% more than when the same number of leaves was removed from the oldest to younger leaves. Continual removal of old leaves reduced new fruit set, fruit weight, and TSS in the 168 day experimental period. Fruit thinning increased new fruit set and ripe fruit TSS. Larger fruit size, faster fruit development, lower respiration rate, and higher sugar contents and AI activity were observed in immature (young) fruit when old fruit were removed. AI activity was reduced during early fruit development and increased again in mature fruit in plants subjected to defoliation, and suggested a role for AI in mature fruit sugar accumulation, while SS activity declined significantly in fruit 154 and 175 days after anthesis and in mature fruit when plants were subjected to continual defoliation. SPS activity was not affected significantly by defoliation or fruit thinning. Source-sink balance was critical for papaya fruit set, development, and sugar accumulation and each mature leaf was able to provide photoassimilate for about three fruit.

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Abstract

Papayas (Carica papaya L.) at seven stages of maturity were harvested in Hawaii and evaluated for differences in intensity of delayed light emission (DLE) and Hunter ‘b’ values. There was a high correlation (r = −0.92) between DLE intensity and Hunter ‘b’ values for freshly harvested papayas at seven stages of maturity. DLE has a high potential as a rapid screening technique for detecting papays that are ripe enough to be susceptible to fruit fly infestation.

Open Access