Abstract. This study was conducted on five year-old apple trees cv. ‘Šampion’, grafted on M26 rootstock and planted in a commercial orchard, situated in eastern Poland, close to Lublin. During the years 1997-1999 the effects of six hand thinning treatments were compared to control trees (no thinning). Different degrees of hand thinning of fruitlets influenced the quality of saleable yield and some other features determining the ‘internal fruit quality’ as: dry matter, soluble solids, sugar and acid content. There were significant differences in values of the examined characteristics between years. In two subsequent years, the highest saleable yield, was obtained from the treatment with most intensive degree of thinning. There were no significant differences in acid content in fruit between the treatment in any year of the study.

The influence of degree of hand thinning on some quality features of apples cv. ‘Šampion’

Summary

The experiment was carried out in a commercial orchard, located close to Lublin, between 1997 and 1999, using ‘Šampion’ apple trees, grafted on M 26 rootstock. The treatments were executed in May: T1 – removal of 50% fruit clusters; T2 – removal of 50% fruit clusters and king flower left intact; T3 – removal of 50% fruit clusters and two lateral fruitlets left intact; T4 – removal of 50% fruit clusters and king flower and one lateral fruitlet left intact; after June drop were made with leaving 1 fruitlet (T5) or 2 fruitlets (T6) with a space of 20 cm between fruit clusters. Unthinned trees were left as the control. To determine the ‘internal quality’ of apples, 75 fruits from every treatment were sampled at the harvest date and analysed for the content of dry matter, soluble solids, sugar and acidity. The intensity of hand thinning influenced the quality of saleable yield and characteristics determined as ‘internal fruit quality’. The mean quantity of saleable yield, dry matter, soluble solids and sugar content were significantly different between the years of the study. The greatest saleable yield in the two subsequent years of study was that after removal of 50% of all fruit clusters and leaving only king fruitlets. However, there were significant differences between most treatments and the control only in 1997. Fruits from trees where 50% of all fruit clusters were removed leaving two lateral fruits, had the greatest dry matter content, significantly higher than in control. There was no influence of thinning treatments on acid content in fruit in each year of the investigation.