Agriculture Reference
In-Depth Information
Roots are, however, a relatively weak sink for assimilates and root growth
can be greatly reduced by 'internal' competition from shoots and fruits. Head
(
) confirmed the general pattern of a peak
of root growth in May and June, ending at the time of vigorous shoot growth
and a second peak in August through October after shoot growth had ended.
Quinlan (
) and Rogers and Head (
) found that when
CO
was supplied to individual leaves on
a rooted apple shoot, labelled assimilate from the youngest (upper)
leaves
moved to the stem apexand young leaves. That from the lower leaves moved to
the roots, each leaf supplying a specific part of the root system. Pruning apple
and pear trees stimulates shoot growth and delays the onset of root growth
(Head,
a).
Even light crops of fruit reduce root growth (Head,
,
)
found that fruiting could lead to a net decrease in root volume of a very
dwarfing apple rootstock, presumably because lost roots were not replaced,
and Hansen (
a). Avery (
) showed that whereas roots accounted for approximately
% of the annual growth increment of deblossomed trees of
- and
-year-old
pot-grown trees of 'Golden Delicious'/'M.
' they accounted for less than
%
of the growth increment of cropping trees. Palmer (
) found that in heavily
cropping field-grown trees of 'Crispin'/'M.
' root weight actually decreased
from the second year in the orchard.
Genotype effects
The more vigorous the stock/scion combination, the larger the root system.
Data from Hatton (
rootstocks, shows a posi-
tive, linear, relationship between the mass of the root system and that of the
tree trunk and branches in a ratio of about
), from trials involving
, although with wide vari-
ations. Any given rootstock had more root mass when combined with the
vigorous 'Bramley' scion than with the less vigorous 'Worcester'. Fernandez
et al.
(
to
) found that the vigour of trees of 'Starkspur Supreme Delicious'
on nine modern apple rootstocks was linearly correlated with the number of
rootstock roots. The slope of the relationship varied with soil type and there
were some deviations from expectation, e.g. 'M.
EMLA' had relatively few
roots in relation to the vigour it induced in the scion. Even dwarfing root-
stocks can, however, exploit the available soil volume at maturity: Rogers
and Head (
) reported 'M.
' roots at
feet (
.
m) in a pocket of deep
soil.
In general the root systems of pear seedling stocks are much more vertically
oriented than those of quince or of the clonal apple rootstocks. Within apple
rootstocks a number of differences in root distribution have been recorded, but
effects are inconsistent and may in part reflect differences in tree management
(Atkinson,
).
