Page 464 - Biosystems Engineering

436 Cha pte r F i f tee n

storage. Hand thinning also caused an increase in starch content (in
9-year-old Lobo trees) and sometimes resulted in earlier ripening as
indicated by a higher Streif’s index.
NAA applied just after flowering, 4 to 5 weeks earlier than hand
thinning, caused similar (in Gala and Gloster cultivars greater (in
Lobo) or sometimes smaller increases in apple size than hand thin-
ning. This may have been connected to the varying sensitivity of cul-
tivars to NAA. However, apples from trees treated with NAA dif-
fered from those thinned by hand; they contained fewer sugars and
starches (especially in “Gala” and “Gloster”), but they also showed
smaller incidences of bitter pit. Apples from these trees rotted less
and showed less shriveling than apples from unthinned trees.
Treatment with BA in general caused an increase in apple size
compared with hand thinning or NAA treatment. Treatment with BA
also limited fruit shriveling during storage. The influence of BA on
the susceptibility of fruit to rotting was not uniform in different culti-
vars (in the Gala cultivar, BA treatment reduced rotting, whereas in
Gloster and Lobo, BA evoked the tendency for more rotting). Firm-
ness and soluble solids content at harvest and during storage in BA-
treated apples were more similar to those in hand-thinned apples
than to those in NAA-thinned ones.
These results indicate that thinning—one of the most important
agricultural measures in modern apple orchards—may modify sev-
eral fruit characteristics influencing the storage ability of apples.
Thinning affects such fruit characteristics as firmness during harvest
and after storage, soluble solids content of the sap, starch content,
mineral composition, incidence of physiological disorders during
storage, and susceptibility to rotting. Of course, the effect of thinning
on storage ability depends on conditions prevailing in the orchard
during the growing season, methods of thinning, and cultivar.
Summarizing the results, we may conclude the following.
Hand thinning, done after the end of June drop, in spite of the late
date of its execution, resulted in bigger fruit, an increase in sugar con-
tent, and sometimes caused higher fruit firmness (especially after
storage) as well as less rotting. Nevertheless, such late hand thinning
may increase the susceptibility to bitter pit. The influence of hand
thinning on the mineral composition of apples was not uniform: in
Lobo apples it caused the augmentation of Ca content without influ-
encing potassium, whereas in Gala apples the level of Ca was not
changed and the content of K and Mg increased. Other authors indi-
cate that storage ability of apples and their quality at harvest depend
on timing of hand thinning during the season and on the localization
of fruits on the tree. 73
Urea applied during flowering influenced the storage ability of
apples differently depending on concentration, date of spraying, and
on the cultivar. A low concentration (0.75 percent, commonly applied
in orchard for fertilization), caused a decrease in Ca level, an increase