MSc

The bio-availability of the toxic heavy metals like cadmium and lead together
with its selective retention sites in tomato (Lycopersicon esculentum Mill.) was one of
the major concerns in the crop. For this, pro-calculated quantities of cadmium and
lead were applied to the soil mainly as water-soluble sources (cadmium chloride and
lead nitrate respectively) to assess the finite objectives envisaged in the study.
In order to meet the objectives, a pot culture experiment was conducted in the
Vegetable Research Farm attached to the Department of Olericulture, College of
Horticulture, Vellanikkara during the rabi season of 2003 with five treatments and
four replications.
Pre-treatment analyses of all basic inputs and soil were carried out to quantify
the possible inclusion of heavy metals from them. After providing pre-calculated
quantities of metals in pots, 42 day old and uniformly grown tomato plants of variety
Sakthi were transplanted to pots. The plants were allowed to establish till majority of
the plants (50 per cent) were at the turning stage. Biometric observations on the plants
due to the impact of the metals were recorded. Fruits as and when they turned ripe
were harvested with proper acknowledgment to their identity in treatments for yield
and its subsequent dry weight. At harvest, the plants were carefully uprooted, cleaned
properly and separated into root and shoot portions. After recording the weight of
each portions, these parts were taken for analysis. Post-harvest soil samples were also
collected and analysed to see the extent of availability of major nutrients and heavy
metals, particularly cadmium and lead. All the inputs including soil maintained
variable amounts of cadmium and lead, with maximum metal load contributed from
phosphatic sources.

It is seen that growth of tomato plants in pots, particularly under the influence of
different levels of cadmium and lead, manifested differential growth and development.
Internally also, the plants exhibited differential metal load and retention patterns apart
from recording variation in the uptake of major nutrients. A brief resume of the major
influence of different levels of cadmium and lead in soil and on the tomato plants is
presented hereunder.
Variation in cadmium levels in soil could influence significant variations In the
available nutrient status in post-harvest soil samples. Accordingly, an increase in
metal load permitted enhanced potassium availability in soil while the same status had
an opposite effect particularly with respect to the available phosphorus and nitrogen.
The nitrogen content of root and shoot of tomato plants was seen to be positively
influenced with higher levels of cadmium application. However, a reverse trend in
nitrogen content was observed with lower levels of application except for the shoot
portions observed from Treatment 4. Among the various plant parts analysed, the
fruits maintained the maximum nitrogen content and this content was roughly
observed to be twice as that of its content in roots. Enhancement in cadmium level in
soil resulted in a corresponding increase in the phosphorus content of roots, shoot and
fruits. As observed for nitrogen, fruit portion maintained the maximum phosphorus
content. A very similar trend was noted for the potassium content in tomato,
consequent to the application of different levels of cadmium.
Much before an apparent growth or' yield reduction was noted in tomato with
cadmium application, the tomato plants readily exhibited certain characteristic
symptoms, which could be associated with the metal toxicity on that plant.
Preliminary indications appeared on leaves with such leaves picking up yellowing and
inter-veinal chlorosis depending upon the metal load. At high concentrations of the
metal, invariable splitting up of the stem at the collar region leading to complete death
of such plants has been noted.

As concentration of the cadmium load increased beyond 1.5 mg kg" soil, the
tomato plants failed to fruit and at the highest concentration of the metal envisaged in
the study (2.0 mg Cd kg" soil), the very establishment of the transplanted tomato crop
was questioned. However, the successful survival and fruiting of the transplanted
tomato plants was noted only at lower levels of cadmium addition (0.5 and 1.0 mg Cd
kg" soil). Lower doses of addition of cadmium had exhibited negative influence on
growth and development in tomato with the manifestation of significant reduction in
number of branches, leaf length, leaf number, plant height, the production of trusses
and subsequent reduction in yield.
Reduction in growth and yield of tomato plants from different levels of application
of cadmium, necessarily brought significant reduction in dry matter yield, whose
influence is clearly reflected in the roots, shoot and fruits portions underlining a
negative influence of cadmium on the dry matter production.
At all levels of cadmium application, there was sufficient retention of the metal in
plant whether it is root, shoot or fruits Roots of tomato are seen to preferentially
harbour more of cadmium than its other plant parts particularly at higher levels of
addition. However, at lower levels of addition, shoots preferred to maintain more
cadmium than its root portions.
Increasing levels of lead invariably decreased the root nitrogen content
.
significantly while shoots content of nitrogen increased generally with lower doses of
metal addition. Variation in, lead levels permitted a significant increase in the
phosphorus content in roots, shoot and fruits. No specific trend was noted in the
retention of potassium by roots while shoot portions indicated significant influence of
the same by offering differential content of potassium in them. Among all the plant
parts, fruits maintained the maximum nitrogen, phosphorus and potassium content.
Higher doses of lead rendered some fruits, if not all with certain malformations.
This together with the total absence of any phyto-toxicity testifies that the tomato

plants are able to tolerate high concentrations of lead inside them. Quite contrary to
the expectations, an unusual increase in dry matter production was observed from lead
treated tomato plants.
Lead application in soil, irrespective of its levels, permitted maximum
accumulation of the metal in fruits followed by shoots and roots. All accumulations
noted in the plant were observed to be significant, projecting serious concern for the
silent inclusion of lead in the economically important part of the plant.
Variable amounts of cadmium and lead have been detected in the post-harvest
soils indicating that the entire quantity of the applied cadmium and lead could not be
completely absorbed by the plant.