Agriculture Reference
In-Depth Information
Plant health
The plant needs to be free of the most important diseases so that it does
not contaminate the fi elds with new pests (disease, insect or nematode).
Occasionally, new weeds can be introduced via the substrate the plants were
grown in.
Anatomical and physical aspect
It is best to use plants that are anatomically well formed with a straight and
strong main stem (Fig. 3.5a). The plants should be healthy and vigorous and
be inspected to make sure they have a good root system and a straight stem
with a good caliper. There should be no pronounced bends in the 'neck' - the
zone that separates the root from the stem - which indicate an improper seed
or embryo position at sowing time. The bends in the neck are due to chance
or bad sowing position plus a lack of proper sorting of the seedlings when
transplanted to the containers, These seedlings should be discarded at the
time of the fi rst transplant in the nursery or at the time of purchase. The bent
condition is more of a problem in seedlings from polyembryonic seeds like
citrus and mangoes of the Indochina-Philippine group. The mangoes of this
group form many embryos, which compete for the space that is normally for
one embryo, resulting in abnormal growth and entanglement and bending.
Plants with bends in the main roots at the bottom of the root-ball or with a
mesh of roots around it indicate they have stayed far too long in the container
(Fig. 3.5b). Ideally plants with these problems should be discarded. If needed
or because of scarcity of planting material they can be used, but the peripheral
roots have to be pruned away and the root mesh disrupted by making several
longitudinal cuts in this layer with a sharp knife. The objective is to ensure
that this abnormal growth pattern does not continue and that new roots
will emerge from the root-ball and grow outwards. When the primary root
at the bottom of the root-ball has a bend, it should be cut above the bend to
eliminate this abnormal growth pattern. This root pruning will result in root
loss and a plant with reduced water and nutrient absorption capacity. The
recommendation is to defoliate the plant to reduce potential transpiration and
balance the root absorption with leaf transpiration. Failure to defoliate can
lead to plant dehydration and death. This defoliation and root pruning will
retard plant growth and therefore all plants with manipulated roots should be
planted together in one area of the fi eld so that they can be given additional
care. Their growth will be initially slightly behind the other transplants that
have intact roots. Similar procedures should be used if the root-ball cracks or
breaks during transplanting, or if too damaged then discard.
