Agriculture Reference
In-Depth Information
stored nitrogen is mainly in soluble form with the amide asparagine always
being an important constituent.
Mason and Whitfield (
) showed that the apple root bark concentration
of K decreased from
.
% in winter to
.
% in early May. Terblanche
et al.
(
) found that Ca is redistributed from roots after resumption of growth in
spring.
Conversion or synthesis of growth regulators
Root-produced abscisic acid (ABA) is an important signal of soil moisture stress
and of impedance to root growth. It helps adapt the plant to these by inducing
stomatal closure and checking leaf and shoot growth (see Chapter
).
Root-produced cytokinins may have important regulatory effects on shoot
budbreak, in relation to release from seasonal dormancy and apical domi-
nance, and on other processes involving cell division.
Itispossiblethatrootresponsesto,orproductionof,plantgrowthsubstances
are involved in rootstock effects. Movement of labelled IAA from scion leaves
into roots of 'MM.
' and 'MM.
' was much greater than that into the
dwarfing 'M.
zeatin
riboside)inthexylemsapofrootstocksincreaseswithrootstockvigour(Kamboj
et al.
,
' and 'M.
'. The content of the cytokinin (zeatin
+
).
Special features of apple and pear
seedling roots
Seedling rootstocks are still widely used for pear and are used to a limited
extent for apple.
Production of seedling rootstocks
The seeds used for seedling production are generally those which are most
readily available as a result of separating the seeds from the rest of the fruit in
the course of fruit processing, e.g. canning or juice production. 'Delicious' is the
most commonly used cultivar. Apple and pear seeds are subject to inhibitory
dormancyfromthefruitanditsjuicesandfromseed-coatdormancy.Theseeds
are thoroughly soaked and washed but with the predominant temperate-zone
cultivars there is then still a need for an appreciable period at low temperature
under moist conditions (Abbott,
). This need for low temperature 'stratifi-
◦
Cfor
cation', usually at
days (Howard,
), is due to physiological deep
dormancy (Hartmann
et al.
,
) which is overcome by meeting the 'chilling
