A high CO2 slow cooling CA storage procedure was developed for `McIntosh' apples (Malus domestica Borkh.). The apples were cooled from 18° to 3°C in 15 days in atmospheres containing a constant O2 at 2.5% and decreasing CO2 starting with 12% and ending at 3%. The results of several tests in a flow-through simulated CA storage system revealed that the new procedure was nearly as effective as rapid CA and was much more effective than traditional slow CA in preserving the firmness of `McIntosh' apples for up to 4 months of storage. Maintaining a constant CO2 either at 12% or 3% instead of gradually decreasing it from 12% to 3% during the slow cooling period resulted in more storage disorders or/and softer apples.
C.B. Watkins and F.W. Liu
The storage potential of ‘Empire’ apples [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] in controlled atmosphere storage has been studied. Fruit were treated with a range of partial pressures of CO2 (pCO2) from 0 to 5 kPa at storage temperatures of 0, 0.5, and 3 °C. The predominant storage disorders that developed were external CO2 injury, flesh browning (chilling injury), senescent breakdown (soft flesh browning), and core browning. All disorders except external CO2 injury increased with longer storage periods. The incidence of external CO2 injury was usually greater with higher storage temperature, whereas flesh browning was worst at lower storage temperatures and senescent breakdown was higher at warmer storage temperatures. The effect of storage temperature on core browning was not consistent. External CO2 injury, flesh browning, and core browning incidences were higher with increasing pCO2, especially above 2 kPa. Flesh firmness was lowest at warmer storage temperatures and in the absence of CO2. Orchard to orchard variation for all factors was high. Relationships of disorders with mineral concentrations were specific to disorder and storage conditions. The results suggest that ‘Empire’ should be stored at 1 to 2 °C, reflecting a compromise between risk of flesh browning at 0 °C and risk of senescent breakdown and unacceptably soft fruit at 3 °C and that pCO2 should be maintained below 2 kPa and closer to 1 kPa.
K. Heuss, Q. Liu, F.A. Hammerschlag and R.W. Hammond
As part of a program to develop transgenic peach (Prunus persica L. Batsch) cultivars with resistance to Prunus necrotic ringspot virus (PNRSV), we are testing a system for measuring virus in peach shoot cultures. Micrografting in vitro is used for inoculation and slot-blot hybridization, with a digoxigenin (DIG)-labeled cRNA probe complementary to the 5′ open reading frame (ORF) of PNRSV RNA 3, for detection. In this study, we investigated whether infected shoots maintain virus infection over long periods of culture at 4 °C and if PNRSV-infected `Suncrest' shoot cultures can serve as graft bases to transmit virus equally well into cultivars Nemaguard, Springcrest, and Suncrest. The results of RNA hybridization analysis showed that virus was present in extracts of leaf samples from 2-year-old PNRSV-infected `Suncrest' shoots that had been subjected to varying lengths of incubation at 4 °C in the dark, suggesting that infected shoots can be maintained for repeated use. Rates of graft success were higher in heterografts between `Suncrest' bases and tips of `Springcrest' or `Nemaguard' than in autografts between `Suncrest' and `Suncrest', and there was equal efficacy of graft inoculation from `Suncrest' into these three cultivars.