Agriculture Reference
In-Depth Information
showed unequivocally the higher cropping efficiency of trees on 'M.
EMLA'
in that they gave significantly higher yields than trees on 'P.
', 'M.
'/'MM.
',
and 'M.
EMLA' which were significantly larger.
By the standards of other crops, apple trees on 'M.
' have a very high parti-
tioning efficiency (harvest index). Hansen (
) showed that fruits represented
more than
% of the total dry matter increment of
- and
-year-old trees
of 'Golden Delicious'on'M.
' rootstocks. Barlow and Smith (
), reporting
on a
-year study of total dry matter production of the cv. 'Laxton's Superb'
showed that more than
% of the dry weight had been in the fruits of trees on
'M.
'. The scope for fur-
ther advance in this respect is clearly limited. However, Callesen (
' as contrasted with
-
% of that of trees on 'M.
) showed
that trees of 'Elstar' on 'J.
% higher ratio of crop to trunk
cross-sectional area than similar-sized trees on 'M.
' rootstock had a
EMLA', and Hrotko,
et
al
.(
) found that trees of 'Idared' on 'J.
' had a
% higher crop to TCA
ratio than that of rather smaller trees on 'M.
'.
Data on cropping efficiency must be interpreted with care. Very small trees,
with their canopy well illuminated throughout, will generally show a high ratio
of crop to tree size and growth. If, however, they are so dwarfed that even at
very close spacings they cannot intercept most of the available light, then the
orchard yield will be low. Moreover the ratio of crop to tree size may depend
on how the latter is measured. Comparative data on widely spaced trees on
different rootstocks will give unbiased estimates of their relative cropping effi-
ciencies. However, once the trees have filled the space allocated to them, e.g.
in hedgerow planting, they will continue to increase in girth and weight even
though their canopy volume and light interception does not increase further
and their apparent cropping efficiency, if expressed, e.g. as yield per unit TCA,
will decline. Where, as in many experiments, trees on rootstocks of differing
vigour are planted at a common within-row spacing, those on the more vig-
orous rootstocks will fill their available space more quickly, and from then
on appear less efficient than they actually are, compared with those on more
dwarfing rootstocks. Yield per unit of canopy volume (Figure
T
) or per unit
light interception may then provide a more useful measure especially if used
in conjunction with the data on total canopy volume or light interception.
.
Effects on fruit quality factors
Size
Rootstocks can influence fruit size in three different ways. First, it is well es-
tablished that shaded areas of apple trees produce smaller fruits, whether the
shade is artificially imposed ( Jackson and Palmer,
) or attributable to po-
sition in the canopy ( Jackson
et al
.,
). It is therefore to be
expected that trees on dwarfing rootstocks in which most of the canopy is well
; Tustin
et al.
,
