Chlorophyll fluorescence was evaluated as a rapid and nondestructive technique to detect low-O2 or high-CO2 stress in apples (Malus domestica Borkh.) during storage. `Marshall' McIntosh apples were held for 5, 10, 15, 20, or 25 days at 3C in 1) standard O2 (2.5% to 3%) and low CO2 (<1%), 2) low O2 (1% to 1.5%) and low CO2 (<1%), 3) standard O2 (2.5% to 3%) and standard CO2 (4% to 4.5%), or 4) standard O2 (2.5% to 3%) and high CO2 (11% to 12%). Only 10% of the apples had skin discoloration after 5 days in 1% to 1.5% O2; 80% developed skin discoloration after 20 days in low O2. Small desiccated cavities in the cortex, associated with CO2 injury, developed in 10% of the apples after 20 days in 11% to 12% CO2. Five days in 1% to 1.5% O2 or 11% to 12% CO2 caused variable fluorescence (Fv) of apple fruit to decrease compared to those held in standard atmospheres. Additional exposure did not significantly affect Fv in either the low-O2 (1% to 1.5%) or high-CO2 (11% to 12%) treatment. Our results suggest that chlorophyll fluorescence techniques can detect low-O2 and high-CO2 stress in apples before the development of associated disorders.
Jennifer R. DeEll, Robert K. Prange, and Dennis P. Murr
Incidence of scald in nontreated and DPA (2000 mg·liter-1)-treated `Delicious' apples (Malus domestics Borkh.) was assessed after 8.5 months in 1.5% or 0.7% O 2 plus 1.5% CO2 at 0.2C, with and without C2H4 scrubbing. Incidence of scald was high in non-DPA fruit held in 1.5% O2, and DPA treatment reduced scald in fruit held in 1.5% or 0.7% O2. Scald control was better with 0.7% O2 and no DPA `treatment than with 1.5% O 2 and a DPA dip. Ethylene scrubbing had no effect on scald in fruit held in 0.7% or 1.5% 02. Susceptibility of fruit to scald-and flesh browning exhibited seasonal variation, which was related to the differences in fruit maturity and the amount of watercore at harvest, respectively. Chemical name used: diphenylamine (DPA).
Storage of `McIntosh' apples (Malus domestica Borkh.) in high humidity (94% to 100% RH) or in 0.5% CO2 plus 1.0% O2 at 3C (LO) atmospheres decreased resistance to ethane diffusion relative to fruit stored in low humidity (75% RH) or in 5.0% CO2 plus 3.0% O2 at 3C (SCA), respectively. Loss of fruit firmness of SCA- or LO-stored `McIntosh' apples, determined immediately after storage or after 7 days at 20C, decreased with increased storage humidity in each of three crop years. Storage humidity did not significantly affect (P = 0.05) fruit titratable acids or soluble solids contents. High storage humidity (96% to 100% RH) generally increased the incidence of senescent disorders (consisting of senescent breakdown and senile brown core) in SCA-stored fruit, while humidities of 92% to 100% RH decreased the incidence of low-O2 injuries (epidermal bluing and cortical browning) in LO-stored fruit. Senescent disorders were found in SCA-stored fruit, but not in LO-stored fruit. The incidence of decay was not significantly affected by either storage humidity or atmosphere.
In a 3-year study, the effectiveness of 0.7% and 1.5% O2 to attenuate scald was evaluated on three strains of `Delicious' apples (Malus ×domestica Borkh.)—`Harrold Red', `Starking', and `Starkrimson'—harvested five times at weekly intervals from a wide range of orchards. Scald susceptibility of fruit held in air, 1.5% O2 + 1.0% CO2, and 0.7% O2 + 1.0% CO2 at 0 °C decreased sharply as the fruit matured on the tree (starch index 1.0 to 2.5 on a 0 to 9 scale). Later harvests (starch index >2.8) further reduced scald but the fruit had more watercore-induced breakdown and were 3 N softer than fruit picked at a less advanced maturity. Early picked `Starkrimson' (starch index <2.0) scalded more than `Starking' and `Harrold Red' in air, 1.5% O2, and 0.7% O2 storage at 0 °C, and 0.7% O2 was less effective than 1.5% O2 in scald control. While 0.7% O2 storage effectively reduced scald (less than 10%) for 8 months in `Starking' and `Harrold Red' picked over a wide range of maturity (starch index 0.7 to 4.3), it did not adequately control scald (up to 45%) in early picked `Starkrimson' (starch index <2.0). Storage in 0.7% also reduced watercore-induced breakdown in `Starkrimson' (starch index >3.0) and did not result in skin purpling or alcoholic taste in `Harrold Red', `Starking', and `Starkrimson'.
Laura J. Lehman and George M. Greene II
A two year study of `Golden Delicious' and `York Imperial' apple responses to delayed cooling and CA storage imposition after harvest was completed in 1991. Apples from six to eight commercial orchards were harvested at an acceptable maturity level for long-term storage, subjected to a delay in refrigeration (0,3, or 6 days) followed by a delay in CA storage imposition (0,14, or 28 days), and then stored at 0°c, 2.4% oxygen, and 1.6% carbon dioxide for up to eight months. Fruit acidity, soluble solids content, bitter pit incidence, scald, internal breakdown, and the development of low oxygen injury were not influenced by the delays. Delays often resulted in more rot and excessive weight loss during storage. Delays in both cooling and CA storage imposition had an additive effect on fruit softening, such that the longest delays resulted in the softest fruit.
James P. Mattheis, David R. Rudell, and Ines Hanrahan
above the low-oxygen limit at 10 °C (0.33 kPa) reported for ‘Honeycrisp’ ( Wright et al., 2010 ), therefore DFB and cavities are unlikely a result of low-oxygen injury. Application of diphenylamine before imposition of CA provides protection from CA
James Mattheis and David R. Rudell
with decreased O 2 kPa may indicate increased CO 2 sensitivity as storage O 2 kPa decreases or may show that the disorder is a form of low-oxygen injury. The low-oxygen threshold identified by monitoring CF in both years was 0.1 kPa less than that