Symptoms of chilling injury were reduced by intermittently warming cucumber fruit (Cucumis sativus L. cv. Poinsett 76) from 2.5 to 12.5C for 18 hr every 3 days. Fruit continuously held at 2.5C for 13 days developed severe pitting and decay after 6 days at 20C, while fruit continuously held at 12.5C or intermittently warmed showed no pitting or decay during subsequent holding at 20C. The increased rate of C2H4 production during the first warming period, from 12 nl·(kg·hr)-1 at 2.5C to 201 nl·(kg·hr)-1 at 12.5C, was significantly greater than that during the second or third warming periods, i.e., 53 to 98 and 53 to 55 nl C2H4/(kg·hr), respectively. Respiration increased 3-fold during the initial warming period, but only 2-fold during subsequent warming periods. Leakage of cellular ions from excised disks of mesocarp tissue was around 6% and 10% of the total ion content of the tissue for control and intermittently warmed fruit, respectively, but increased to 17% for fruit that were continuously held at 2.5C for 10 days. After 320 hr (three cycles) of chilling and warming, chilled fruit showed significantIy lower ethylene-forming enzyme activity than the control or intermittently warmed fruit. Fruit held at 12.5C contained 0.09 to 0.34 nmol·g-1 of ACC. ACC levels were 6.23 nmol·g-1 in fruit exposed to 2.5C for 320 hr. In contrast, intermittently warmed fruit only showed 30% and 27% increases in ACC content during the first and second warming periods, respectively. Periodic warming appears to allow chilled fruit to acclimate to subsequent periods of chilling. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).
Roberto M. Cabrera and Mikal E. Saltveit Jr.
Mikal E. Saltveit Jr. and Roberto M. Cabrera
Tomato fruit (Lycopersicon esculentum Mill., cv. Castlemart) either harvested hot (e.g., 32°C) and chilled for 7 days at 7°, or harvested cool (e.g., 19°) and held in the laboratory at 37° for 7 hr before chilling at 2.5° for 4 days ripened slower (a symptom of chilling injury) than fruit that were either harvested cool (19°) or held at 12.5° for 7 hr before chilling.
Roberto M. Cabrera, M.E. Saltveit, and K. Owens
Cucumber fruit (Cucumis sativus L.) of 13 cultivars were chilled at 2.5C for up to 10 d, Pitting scores after 8 d at 2.5C and 6 d at 20C ranged from 0.0 (none) in `HP 138' to 7.7 (severe) in `Poinsett 76' fruit. Ion leakage, as the increase in conductivity in a 0.3 M mannitol solution bathing excised disks of mesocarp tissue and expressed as % of the total ion content of the tissue, was lowest in `MDR I' (4.5%) and highest in `HP 159' (11%) after 6 d at 2.5C. After 10 d at 2.5C, however, the lowest was in `Navajo' (5.5%) and the highest in `Poinsett 76' (15%). Resistant lines, e.g., `Dasher II' and `HP 138' showed ion leakage of 7.6% and 5.4% after 6 d, and 8.4% and 7.5% after 10 d. Exudates from cut fruit were collected on filter paper. The fresh and dry wt of exudates from fruit held 8 d at 12.5C ranged from 144 to 346 mg and 16 to 47 mg, respectively. Conductivity of the exudates was highest in `PS 34885' (177 uSiemen/cm) and lowest in `Rawa' (83 uS/cm). The fresh wt of exudate from 6 lines ranged from 99 to 164 mg after 10 d at 2.5C followed by an additional 2.4 d at 20C. The % solid-of the exudates was higher in more resistant lines, e.g., `Dasher II' (8%) and `HP 138' (4%) than in more sensitive lines, e.g., `Poinsett 76' (2%) and `MDR I`(2%). Conductivity of the exudates from chilling sensitive lines were higher than from resistant lines, 60 vs. 30 uS/cm, respectively.
Roberto M. Cabrera, Mikal E. Saltveit Jr., and Ken Owens
The physiological responses associated with chilling of horticulturally mature cucumber (Cucumis sativus L.) fruit were examined using 13 lines that differ in chilling sensitivity. The low correlation coefficient between pitting and decay suggested that these two early manifestations of chilling injury are not significantly related. Likewise, fruit pitting and decay were not highly correlated with the tolerance of seedlings to chilling, suggesting that fruit and seedlings of the same line may have dissimilar sensitivity to chilling temperatures. Exudates from fruit cut in half transversely were collected on filter paper. The amount of exudate showed a significant correlation with pitting, decay, and percent ion leakage after 10 days of chilling. The fresh and dry weight of the exudates from fruit kept for 8 days at 12.5C ranged from 141- to 346-mg fresh weight and from 15 to 47-mg dry weight, respectively. Cucumber lines that were more sensitive to chilling had watery exudate, as indicated by their lower dry weight and percent solids. The conductivity of exudates from sensitive lines was higher (60 μsiemen/cm) than from chilling resistant lines (30 μsiemen/cm). Chilling-induced ethylene production was higher in sensitive than in resistant lines, and chilling caused a greater loss of ethylene forming enzyme activity in resistant lines than from chilling sensitive lines.