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.
The patterns of concentrations of CO2 and C2H4 in the cavity of attached ripening papayas (Carcia papaya L. cv. Solo) were similar to those of CO2 in respiration and C2H4 production in detached ripening fruits. The peak concentrations of these gasses occurred when the surface color of the fruits was about 80%. The flavor of the pulp of the ripe fruit was rated highest at this time.
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.
Subsoil from an acid soil series was amended with CaSO4, MgO, or Ca(OH)2 to identify chemical factors that may enhance papaya (Carica papaya L.) root growth in these soils. Root length of `Red Lady' and `Waimanalo' seedlings at two stages of development was increased by the addition of each of the materials. The increase in root length was similar for CaSO4 or MgO amendments, and was greatest for Ca(OH)2 amendment. These amendments increased dry weight of new roots for `Red Lady' and increased root length per unit dry weight in one experiment for `Waimanalo'. The results indicate that both Ca deficiency and Al toxicity may be responsible for limiting papaya root growth in the subsoils of the acid soils of Guam. Correcting these chemical factors should improve rooting depth, thereby increasing the volume of soil from which resources are accessible and lessening the susceptibility to toppling during tropical cyclones.
The effects on germination of two lots of Carica papaya seed of dehydration at 25 °C, followed by exposure to -20 °C or -196 °C, were evaluated with and without gibberellic acid (GA3) treatment. In the absence of GA3 treatment, dehydration increased subsequent germination only in seed lot 1 when moisture content (m.c.) was reduced from 59% to 6.0% and 5.3%. In seed lot 2, dehydration followed by exposure to -196 °C increased germination compared with dehydration alone. Treatment with GA3 enhanced germination rate in all treatments. Dehydration to 5.3% (lot 1) or 6.9% and 6.8% m.c. (lot 2), followed by exposure to subzero temperatures and treatment with GA3, were the most favorable combined treatments to enhance papaya seed germination. The results suggest that papaya seed presents an orthodox behavior, permitting germplasm conservation in conventional and cryogenic genebanks.
Using the puree juice of 1/2 fruit for soluble solids determination, it was found that for freshly harvested fruit to meet the min % soluble solids (SS) of 11.5 required by Hawaiian grade standards for marketable papayas, the fruit should have at least 6% surface yellow coloration. For postharvest ripened fruit, the min degree of surface coloring when harvested should be as least 3% for the ripened fruit to meet the min soluble solids (SS) requirement. Because the 6% surface coloration is more readily visible than the 3% level in the papaya orchard, the higher stage of coloration is recommended as a index for min harvest maturity.
Exposure of fruits of papaya (Carica papaya L.) to subatmospheric pressure (20 mm Hg, 10 C, 90-98% relative humidity for 18-21 days during shipment in hypobaric containers from Hilo, Hawaii, to Los Angeles and New York inhibited both ripening and disease development. Fruits ripened normally after removal from the hypobaric containers, but abnormal softening unrelated to disease occurred in 4-45% of fruits of one packer. Hypobaric-stored fruits had 63% less peduncle infection, 55% less stem-end rot, and 45% fewer fruit surface lesions than those stored in a refrigerated container at normal atmospheric pressure. Postharvest fungicide-wax applications further decreased disease incidence.
Biolistic genetic transformation of plants with viral genes is a method for controlling plant virus diseases; however, optimization of the particle bombardment parameters according to the transformation system is a key factor for an appropiate transgene expression and, therefore, a stronger resistance mechanism in transgenic plants. In order to optimize biolistic parameters, somatic papaya (Carica papaya L.) cv. Maradol embryo masses were bombarded with the CAMBIA 1301 plasmid construction that contains the coat protein gene (CP) of the papaya ringspot virus isolate of Colima, Mexico, driven by the double constitutively CaMV 35S promoter and flanked for the GUS and hygromycin (hpt) resistance genes. Particle bombardment protocol was carried out using the Helios™ Gene Gun device (BioRad) and the manufacturer's instruction manual. Helium pressure (50, 100, and 150 psi) and gold particle size (0.6, 1.0, and 1.6 μm) were evaluated. Five days after bombardment, somatic embryo clusters were used for GUS transient expression and, during 2 months, were selected into 50, 75, and 150 mg·L-1 hygromycin-containing media to its later CP-PCR detection. Results showed that 50 psi and 1.0 μm were the two optimal values for the assayed analyses. This is the first report of genetic transformation of papaya using the Helios™ Gene Gun device as a new tool compared to conventional PDS-1000/He.
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.
Trade winds occur throughout the year and drought occurs seasonally in many papaya (Carica papaya L.) production regions. We conducted four studies with `Known You 1' and `Sunrise' papaya seedlings to determine the combined influence of wind and water deficit on growth. We conducted three additional experiments to determine plant response to wind within a continuous dose range of 0 to 2.5 m·s–1. The main effects of wind and irrigation significantly reduced most response variables, such as dry weight components, leaf area, and height. However, the two factors acted independently of each other for every measure of plant growth. Thus, there was no departure from simple effects of an additive model for each main factor. The relationship between plant growth and wind between 0 and 2.5 m·s–1 could be described by a quadratic model. Results indicate that the influence of wind on plant growth cannot be studied without controlling or quantifying soil moisture among treatment groups. Practically, our results indicate that wind protection of young papaya plants may be warranted more so in the dry season than in the wet season or under sufficient irrigation practices.