Harvest date, cultivar, orchard, and tree effects on water vapor permeancein apples

Research quantified contributions to total variation in water vapor permean ce from sources such as cultivar and harvest date in 'Braeburn','Pacific Ro se','Granny Smith', and 'Cripps Pink' apples [Malus sylvestris (L,) Mill. v ar. domestica (Borkh,) Mansf,]. In a study on 'Braeburn' fruit from eight o rchards in Central Otago, New Zealand, >50% of the total variation in perme ance was associated with harvest date. This variation was the result of a l arge increase in water vapor permeance from 16.6 to 30.2 (SE = 0.88, df = 1 92) nmol.s(-1).m(-2).Pa-1 over the 8 week experimental harvest period. Frui t to fruit differences accounted for 22% of total variation in permeance, i nteraction between harvest date and orchard effects explained 7% of the tot al variation, indicating that fruit from the different orchards responded i n differing ways to advancing harvest date, Tree effects accounted for only 1% of the total variation. Weight loss from respiration [at 20 degrees C a nd approximate to 60% relative humidity (RH)] comprised 3.04 +/- 0.11% of t otal weight loss, averaged across all harvest dates. In a second study of f ruit of four apple cultivars, almost 30% of the total variation in water va por permeance was associated with cultivar differences. Mean water vapor pe rmeance for 'Braeburn','Pacific Rose','Granny Smith', and 'Cripps Pink' fru it was 44, 35, 17, and 20 (sE = 4.3, df = 300) nmol.s(-1).m(-2).Pa-1 respec tively. Over 20% of the total variation was associated with harvest date an d arose from a large increase in water vapor permeance from 21 nmol.s(-1).m (-2).Pa-1 at first harvest to 46 nmol.s(-1).m(-2).Pa-1 (SE = 5.3, df = 200) at final harvest, 10 weeks later, on average across all four cultivars, Th ere was large fruit to fruit variation in water vapor permeance accounting for 25% of the total variation in permeance values. Tree effects only accou nted for 4% of the total variation. Water vapor permeance in 'Pacific Rose" and 'Braeburn' increased substantially with later harvest but values remai ned relatively constant for 'Granny Smith' and 'Cripps Pink'. A simple math ematical model was developed to predict weight loss from 'Braeburn' fruit. Based on these findings, it appears worthwhile to increase the stringency o f measures to control weight loss in 'Braeburn' and 'Pacific Rose" apples, particularly those harvested late in the season.