sodininkystė ir daržininkystė 25(4)

The main objectives of planting trees on vegetative rootstocks are: regulation
of tree size, growth rate and crown volume, induction of early bearing and high
cropping, adaptation of root system to existing soil and climatic conditions (water
deficit toleration, winter hardiness, etc.). Expected beneficial effect on quality of
fruit is often listed at the end of objectives. However, the influence on fruit quality
in an existing worldwide overproduction of apples becomes now more important
issue.
According to Webster and Hollands (1999), we knew still too little about interactions
between rootstock and scion. Rootstock and scion cultivar affect each
other mutually, therefore each combination of those components should be treated
separately (Schneider et al., 1978). The most commonly used in Europe rootstock
M.9 is lately more often criticized (Groot, 1997; Riesen and Husistein, 1998). Studies
on similar crown volumes trees suggest that the more dwarfing rootstock the
better light penetration and photosynthetic productivity could be observed (Baugher
et al., 1994). This logically should influence the whole tree performance and most
importantly – fruit quality. According to Kader (1985), quality is a combination of
features including appearance, texture, flavour, nutritive value and safety. Consumer
demands are already high for flesh firmness and taste (Autio et al., 1996). For citrus
fruit the influence of rootstock on quality is already well defined (Castle, 1995). For
‘Jonagold’ fruit (and its sport’s as well) flesh firmness is considered to be the most
important parameter, which by 50% decide internal components of quality (Pladett
et al., 1992). Soluble solids content and acidity in an equal share contribute to the
remaining part of those components. Balanced sugars and acid ratio in apple fruit
could provide sweet but refreshing taste. The latter may occur only when appropriate
acid content is maintained (Vangdal, 1985; Sekse, 1992). For commercially important
apple cultivars such as ‘Jonagold’, there are already known minimal values
for their acceptability in a selling period – soluble solids should be within 13–14%
and flesh firmness no lower than 45 N (Hoehn et al., 2001).
The objective of our study was to compare the effect of new Polish rootstocks
and well-known English ones on the main quality features of ‘Jonica’ apples.
Materials and methods. The experiments were carried out on ‘Jonica’ trees
planted on rootstocks of Polish selection: P 22, P 59, P 60 and of Malling Series: M.26,
M.9. The studies were realized in the period of the beginning of full production capacity
of the experimental orchard (4–6 years after planting). Trees were planted at a
spacing of 4 x 1.2 m, in four, 5 trees per each replication. Each 6 th tree in a row was a
pollinator – ‘Ðampion’. All trees were trained as slender spindle. From the middle of
September, fruits from boundary rows around experimental plots were sampled in
weekly intervals for optimum harvest date evaluation. Fruits were picked when Streif’s
harvest index values calculated according to formula F(RS) -1 were within recommended
range (Streif, 1983). Mean fruit size (as weight in grams) and percent of blush
coloured area were evaluated on a 100 fruit sample. Fruit quality evaluation and analysis
(fruit flesh firmness, soluble solids content, titratable acidity, starch pattern, etc.)
were carried out according to standard methods (Johnson, 1992). The analyses were
performed at optimum harvest date and respective ones after storage for 6 months,
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