Chilling injury (CI) of ‘Honey Dew’ muskmelons (Cucumis melo L.) induced by 2½ weeks of storage at 0 or 2.5°C is characterized by a reddish-tan discoloration of the surface. Affected areas may be diffuse or discrete. CI was less severe at 2.5° than at 0°C and was absent at 5°C. The diffuse type of discoloration disappeared during 3 days at 20°C, particularly if the melons had reached full rather than only minimum horticultural maturity at harvest. Melons of minimum maturity accounted for 44% of the samples, but for 77% of those with CI.
The symposium “The Medfly in California: The Threat, Defense Strategies, and Public Policy” was held on June 22, 1982, at the University of California, Santa Barbara, in conjunction with the annual meeting of the Western Region of ASHS and of the AAAS-Pacific Division. The symposium was arranged to facilitate communication between members of diverse professional backgrounds about a tremendous potential danger to the horticultural industry of California and to provide as factual a record as possible about the events of 1981 and 1982 and their background. In addition to the topics covered herein, “Environmental and Public Health Concerns” was also discussed but is not included in this compilation. However, the potential health hazards involved in eradicating and in not eradicating the Mediterranean fruit fly (medfly) are alluded to in some of the other contributions.
Romaine lettuce (Lactuca sativa L.) was stored for 2 weeks at 0°, 2.5°, or 5°C with O2/CO2 (%/%) levels of 21/0 (air), 20/5, 20/7.5, 20/10, 20/15, 20/20, 20/30, 0.25/0, or 0.5/0. Controlled atmosphere combinations of 20/15, 20/20, and 20/30 resulted in brown, sunken patches on the green lamina at all temperatures. The 20/10 treatment induced this injury only at 0° and 2.5°, whereas 20/7.5 induced it only at 0°. No injury developed in 20/5 or 21/0. Brown stain, a typical symptom of CO2 injury on midribs of crisphead lettuce, was absent in 20/30, 20/20, 20/5, and 21/0, but developed in the other atmospheres, mainly at 0°. Low levels of O2 (0.5% or 2%) combined with 7.5% CO2 did not consistently enhance sensitivity of romaine to CO2 injury. Salability was retained at least as well in romaine stored at 0° or 2.5° in air as in any of the controlled atmospheres.
I am delighted to have been appointed Science Editor of our Society and I will make every effort to help maintain “the quality and credibility of information published by the Society”, as required by the job description.
Before undertaking this survey of senescence in stored leafy vegetables, I thought that there would be a wealth of information available from which I could draw. I was in for a surprise. Even though there exists ample literature on some symptoms of senescence among leafy vegetables, amazingly little research has been published regarding fundamental changes in their physiology as senescence progresses. Among the roughly 100 papers I checked for this presentation, only a few dealt with any basic aspect of hormonal influences on senescence in leafy vegetables (2, 15, 40, 47, 57). I was amazed by this relative neglect of studies of senescence in a group of crops that are of major economic importance. If this symposium does little more than point to where the gaps in knowledge are, it can be considered a success.
Tomatoes were grown at Tucson in plastic covered greenhouses with normal or high relative humidity (RH). The fruits were exposed to the sun (Ex) or shaded by foliage (Sh), and some exposed fruits were painted either black (B) or white (W).
Temperatures of the surface (Ts), wall (Tw) and center (Tc) of the fruit were 2 to 3° C lower in high than in normal RH, even though the maximum air temperature (Ta max) in high RH exceeded that in normal RH by 1.5°. When Ts and air temperature (Ta) were measured simultaneously, Ts of Ex and B fruits was always higher than Ta, that of Sh fruits lower, and that of W fruits about the same as Ta. The exact gradient depended on RH and Ta.
Tw of Ex fruits almost invariably exceeded Ts or Tc, and thus the wall was a heat sink. Further, Tc max exceeded Ta max in small (diam 35 to 40 mm) or large (diam 60 mm) fruits.
The gradient Tc−Ta for large Ex fruits grown in normal RH ranged from −5° to 15° C during the day, while that for fruits grown in high RH ranged from 0° to 12°. The respective daily ranges for the gradient Tw−Ta were −5° to 20° and 0° to 13°. For small fruits all gradients were similar and ranged from 3° to 13°.
The incidence of defective coloration of the shoulders or sides of fruits was highest in Ex and seemed to be influenced by infrared and short-wave radiation. The possibility of protecting tomatoes from excess radiation is discussed.
Near ultraviolet radiation appears to be largely responsible for solar injury (SI) and vein tract browning (VTB) of cantaloupes (Cumis melo L., Reticulatus group, cv. PMR 45) grown under field conditions in the San Joaquin Valley of California. Incidence and severity of SI were substantially reduced when near UV flux impinging on the fruits at solar noon was reduced to 21 Wm-2 or less and especially when wavelengths below 320 nm were excluded by the use of plastic UV filters. VTB was reduced when UV flux was 12 Wm-2 or less or when wavelengths below 320 nm were excluded. In cantaloupes, near UV appears to directly induce SI but to indirectly induce VTB, a postharvest disorder, by accelerating aging of surface tissues.
A method is presented to calculate net heat gain per unit time (G) for normal (N) and for whitewashed (W) cantaloupe fruits (Cucumis melo, L., var. reticulatus Naud.) exposed to direct solar radiation. Calculations of G were based on pulp temp. G of the W fruits averaged 80% of that for the N fruits during warming. Values of G can aid in evaluating the effectiveness of radiation-reflective materials that protect cantaloupe fruits from sunburn, a major cause of culls and market quality losses. Maximum pulp temp about 1 mm below the surface reached 49°C for the N and 42° for the W fruit. Maximum ambient air temp was 43°C.
The concentration of photosynthate in midribs of crisphead lettuce at various times of the day may be involved in the susceptibility of this crop to various postharvest disorders (3). Measuring the soluble solids content (SSC) of the juice expressed from midribs is simple when a hand-refractometer is used, and would be an ideal method for field use. However, lettuce is low in sugar content (5); thus, SSC may be no more of a valid measure of sugar content in lettuce than in cucumbers, which also have a low sugar content (4). Consequently, we adapted (1, 7) procedures for the determination of glucose, fructose, and sucrose, the principal sugars in head lettuce (type not specified, 5) to midribs of crisphead lettuce utilizing HPLC.