In a 2-year study, the benefits and risks of an initial low O2 stress treatment (ILOS; 0.04 kPa O2 for 10 days) as a supplement to 1.5 or 0.7 kPa O2 storage for controlling scald in `Starkrimson Delicious' apples (Malus ×domestica Borkh.) were evaluated. The fruit were picked from 15 orchards and harvested over five successive weeks to generate a wide range in maturity. Storage in 0.7 kPa O2 did not adequately control scald in fruit picked at starch index between 1.0 and 2.1 (10% to 35% scald), but reduced watercore-induced breakdown in fruit picked at starch index ≥2.4 (0–9 scale). The ILOS treatment gave a statistically significant but commercially nonsignificant scald control benefit to fruit held in 1.5 kPa O2 in 1 year, but not to fruit held in 0.7 kPa O2. ILOS did not increase alcoholic taste, but increased skin purpling in 0.7 kPa O2-stored fruit from the final harvest in 1 year. ILOS decreased flesh firmness in fruit picked at starch index ≥1.7 and increased watercore-induced breakdown in fruit picked at starch index ≥2.1 in both years.
Tolerance of apples to low levels (0.5%) of O2 was cultivar-dependent. `Spartan' (SP), `Delicious' (RD), and `Golden Delicious' (GD) apples (Malus domestica Borkh.) held for 7 months in 1.0% O2 (with 1.5% CO2) at 0.5C, plus ≈2 months in air at 0C and 7 days in air at 20C, were similar to those held in 1.5% O2. However, incidence of skin injury in fruit held in 0.5% O2 was very high in SP (purple-brown discoloration), low in RD (purple-brown discoloration), but only negligible in GD (lesions). Skin discoloration in SP and RD developed rapidly in air at 20C. Holding in 0.5% O2 improved retention of flesh firmness and juice acidity in GD and, under certain conditions, reduced scald in RD and SP, delayed yellowing in GD, but increased flesh breakdown in SP, flesh browning and alcohol flavor in SP and RD, and core browning in RD.
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'.
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).
O.L. Lau and R. Yastremski
`Golden Delicious' apples (Malus domestics Borkh.) were subjected to either 0C controlled-atmosphere (CA) storage or to a postharvest coating of 1.0% to 2.5% Nutri-Save (NS; a polysaccharide derived from shellfish) plus air storage. NS-coated apples were greener and firmer and had higher titratable acidity (TA) and more shrivelled and injured fruit than the control after storage in air at 0C for 5 to 6 months and ripening in air at 20C for 7 days. Poststorage washing increased skin injury, and low relative humidity during ripening increased shriveling of NS fruit. NS applications led to an accumulation of CO2 and C2H4 and a small reduction of O2 in the fruit core cavities. The use of 1.5% O2 + 1.5% CO2 in the storage atmosphere was more effective than NS plus air storage in maintaining flesh firmness (FF) and TA without increasing fruit shrivel or skin injury. NS treatments maintained FF and a green skin in fruit ripened in air at 20C for 2 or 4 weeks following harvest, but some shrivel was evident by 4 weeks. Better retention of skin greenness was the only benefit derived from a poststorage NS treatment of CA-stored fruit during the shelf-life test.
William D. Wolk, O.L. Lau, G.H. Neilsen, and Brian G. Drought
A study was undertaken to identify key factors associated with storage disorders in three commercially important apple cultivars in British Columbia and to determine how early in the season associations could be measured. Fruit mass, density, and concentrations of N, P, K, Ca, Mg, and dry matter were determined for `McIntosh', `Spartan', and `Golden Delicious' apples (Malus ×domestica Borkh) from ≈30 commercial orchards 9, 6, 3, and 0 weeks before harvest. Storage samples were collected at commercial harvest and evaluated for the development of internal breakdown (`McIntosh' and `Spartan') or bitter pit (`Golden Delicious') after 4 and 6 months of 0 °C air storage. Mass and [Ca] and the mass/[Ca] and [K]/[Ca] ratios were the factors most often significantly correlated with storage disorders within each year for all three cultivars. Correlations were as frequently significant 6 and 3 weeks before harvest as they were at harvest. Mass of `McIntosh' and `Spartan' was the only variable consistently related with breakdown in all 3 years of the study. There were no variables with a consistent relationship to bitter pit in `Golden Delicious'. Fruit [Ca] was associated with the relative levels of disorders within years but could not be associated with specific levels of disorders across all years.
G.H. Neilsen, P. Parchomchuk, W.D. Wolk, and O.L. Lau
Newly planted `Jonagold' and `McIntosh' apple (Malus domestica Borkh.) on M.26 fertigated with Ca(N03)2 showed increased early tree vigor and leaf Ca concentration but decreased leaf Mg and Mn compared to trees fertigated with urea or NH4N03. Fertigation with P increased early tree vigor, leaf and fruit P concentration, and decreased leaf Mn in the first year relative to a single planting hole application of granular P. Increased fruit Ca concentration in `Jonagold' in one year was associated with the use of Ca(N03)2 and fertigation of P. Fruit quality was generally unaffected by the experimental treatments.
Yiping Gong, Peter M.A. Toivonen, O.L. Lau, and Paul A. Wiersma
Apple fruits (Malus domestica Borkh. cv. Braeburn) harvested from two orchards (A and B) on the same day were stored in air or pretreated in air for 0, 2 (2dCA) or 4 weeks (4dCA) before moving into controlled atmosphere (CA) storage with 1.5% O2 + 5% CO2. During storage at 1 °C for 9 weeks in air and/or CA, changes of pyruvate decarboxylase (PDC) activity, alcohol dehydrogenase (ADH) activity, acetaldehyde (AA) and ethanol (EtOH) concentrations in flesh tissue were assayed in addition to the incidence of Braeburn browning disorder (BBD). Immediate introduction to CA conditions induced the development of BBD with the highest incidence 62.2%, however delaying application of CA for 2 and 4 weeks reduced the incidence of BBD to 38.5% and 27.0%. The development of disorder in grower B was less than in grower A. 2dCA and 4dCA treatments did not influence PDC activity compared with treatment of CA. However, ADH activity and the accumulation of AA and EtOH in treatments of 2dCA and 4dCA were markedly lower than those in CA. The accumulation of AA in grower B was lower than grower A. The results of this study suggest that the delayed application of CA reduced BBD and this may be due to reduced anaerobic metabolism of fruits in the delayed CA.