PREDICTION OF OPTIMUM HARVEST DATE OF APPLES
In experiment 1 the influence of bloom date on fruit maturity and storability of 'Gloster' apples was investigated in the years 1990 and 1991 and of 'Elstar', 'Golden Delicious', 'Idared', 'Jonagold' and 'Jupiter' in 1991. During bloom, spurs with successively opening blossoms were marked every third day. All fruits were harvested at the same time. Incidence of physiological fruit disorders was recorded after six months in cold storage.
Experiment 2 involved determination of harvest date of apples. In the years 1991–1993 investigations were carried out on 'Gloster', 'Cortland', 'Spartan' and 'Lobo' apples from 17, 25, 21 and 17 commercial apple orchards of Central Poland. Wide variability of individual fruits within a tree as well as of trees was found within an orchard block, in respect to fruit maturation and subsequent storability. This variability was apparently associated with the differences in bloom time. Fruits developed from late blooming flowers were considerably smaller than those from early blooming ones. Fruits from late blooming flowers produced less ethylene, exhibited a lower starch index and developed superficial scald during storage. This indicates that apple cultivars with a prolonged bloom period should be harvested at least twice. Besides, in all the cultivars under examination in experiment 2, a significant correlation between starch index and internal ethylene concentration was found; hence the starch index may be a good criterion for determination of optimum harvest time