Coconut Research Institute Repository

Meegahakumbura, M.G.M.K.

Perera, L.

Padmasiri, M.H.L.

Chandrasiri, S.A.S.

New dimensions of coconut breeding in Sri Lanka for the 21st century

Peiris, T.S.G.

Waidyarathne, K.P.

Samitha, S.

Thattil, R.O.

Control of spatial effect due to neighboring palms in coconut (Cocos nucifera) experiments

Senarathne, S.H.S.

Wild sunflower use as a organic fertilizer in coconut plantations

Jayakody, J.A.D.S.S.

Tennakoon, N.A.

Fernandopulle, M.N.D.

Available soil phosphorus in coconut platations in boralu and pallama soil series, under different fertilizer regimes in Gampaha district of Sri Lanka

Nainanayake, A.D.

Use of chlorophyll fluorescence parameters to assess drought tolerance of coconut varieties

Madurapperuma, W.S.

Mendis, H.

Ranasinghe, C.S.

Premasiri, N.

Gunawardena, M.

COCOS (2007), 18 1 6 - 2 3 
Printed in Sri Lanka 
A COMPARATIVE STUDY OF WATER MOVEMENT IN LEAF SCORCH 
DECLINE AFFECTED AND HEALTHY COCONUT PALMS USING 
LITHIUM AS A NON-RADIOACTIVE TRACER 
W.S. Madurapperuma, H. Mendis, C.S. Ranasinghe, 
N. Premasiri and M. Gunawardena 
Coconut Research Institute, Lumiwila, Sri Lanka 
ABSTRACT 
Obstructions to the movement of water, by physical blockages in the vascular system, are 
a possible cause of the Leaf Scorch Decline (LSD) disorder of coconut palms. This 
hypothesis was tested by comparing the pattern of water movement in healthy and LSD-
affected coconut palms, using Lithium, a non-radioactive tracer, as an indicator. Pattern 
of water transport in the leaf canopy of healthy and LSD-affected palms was similar but 
the quantities transported were different. Less water movement in moderate-LSD palms 
than in healthy and mild-LSD palms suggest the development of obstructions to water 
movement when the disorder increases in severity. Uptake of water into the root system 
was not affected by the LSD disorder. However, in moderate-LSD palms more water was 
retained in the roots than in healthy and mild-LSD palms. This also points to restrictions 
to water movement in the moderate-LSD palms, The relatively high amounts of Li 
retained in the roots of healthy and mild-LSD palms need further investigation. 
Key words: Leaf Scorch Decline, visible symptoms, pattern of water movement, non­
radioactive tracer 
INTRODUCTION 
The characteristic visible symptom of the Leaf Scorch Decline (LSD) disorder is leaf 
scorch that starts from the tips of the leaflets and advances towards the midrib of the frond 
(Davis, 1962;Ekanayake, 1964, Rajapaksha and Fernando, 1995; Madurapperumaetal, 
2004; Ranasinghe, 2005). Scorch first appears on the physiologically less active mature 
fronds (mild stage of LSD), and advances progressively to the younger fronds of the 
middle whorl of the canopy (moderate LSD) and to still younger fronds (severe stage). 
The other symptoms that develop progressively in moderately and severely affected 
palms are: a reduction in the length of newly emerging fronds; number and size of 
inflorescences, nut set and yield; and bearing abnormally elongated nuts, and tapering of 
the trunk (Peries, 1968; Rajapaksha and Fernando, 1995; Madurapperuma et al., 2004; 
Ranasinghe, 2005). 
Physiological studies with LSD-affected coconut palms have demonstrated a significant 
reduction in the transpiration rate, photosynthesis and leaf water potential (LWP); and an 
increase in leaf stomatal resistance and ABA concentration in the xylem sap, in 
16 
comparison to healthy palms (Jayasekara et al, 1989; Ranasinghe, 2005). This suggests 
that LSD-affected palms are water stressed. Even with the soil moisture level at field 
capacity (FC), the LWP of LSD-affected palms was lower than in healthy palms 
(Jayasekara et al, 1989), which points to an internal water deficit condition in LSD 
palms. This condition could be attributed to either poor water absorption due to a paucity 
of live roots in LSD-affected palms (Jayasekara and Premasiri, 1986; Mahindapala and 
Chandrasena, 1975; Ranasinghe et al, 2002), or physical blockages in the water 
transport tissues. 
Physical barriers in the vascular system limiting the movement of water to plant tissues 
will also restrict the supply of nutrients to these tissues and retard growth. Nutrients 
absorbed by the roots are moved upwards with the transpiration stream. Hence the 
efficiency of nutrient uptake will depend on the physiological status of plants 
(VidanaarachchiandNor, 1994). 
Clearly, in plants under physiological stress the uptake of water and nutrients is 
inevitably reduced. Generally, when the stress factors are removed the plants recover. 
However, LSD-affected coconut palms suffer from water stress even under optimum 
environmental conditions. It may, therefore, be assumed that physical blockages in the 
vascular system are involved. The foregoing leads to the hypothesis: water movement 
from roots through the trunk to the crown of LSD-affected palms is restricted by physical 
blockages in the vascular system. This study aims to test the hypothesis, and identify the 
zones where restrictions occur, using Lithium as a non-radioactive tracer. 
MATERIALS AND METHODS 
Li, a non-radioactive tracer, was used to study the water transport pattern in LSD-
affected coconut palms. The advantages of Li are its low cost, availability of simple 
analytical methods, and that it is measurable at very low concentrations (0.01 or even 
lesser). Moreover, Li occurs naturally in soils at very low concentrations, and when 
added to the soil it is taken up freely into the shoot system (Martin et al, 1982). Hence, 
the concentration of Li in different plant tissues, after application of Li, will be a measure 
of the amount of Li as well as the amount of water that has moved into different tissues 
(Ranasinghe and Wijerathne, 2005). 
The experiment was conducted at Poththukuluma Research Station in the agro climatic 
region IL3. Thirty-year-old coconut palms, of the Tall variety (van typica), uniformly 
managed as per recommendations of the Coconut Research Institute were selected for 
the study. Six palms each with mild-LSD and moderate-LSD (as described in 
Ranasinghe, 2005) and apparently healthy palms were selected for the experiment. 
Palms that had advanced beyond the moderate stage of LSD were not selected for this 
study as their response to treatments was poor (unpublished data). A Randomized 
Complete Block Design with six replicates per treatment was used for the experiment. 
17 
A sunny day (light intensity between 1200-1500 (imol m V ) was selected for root 
feeding. A 100 ml of 1% LiCl solution was prepared for root feeding of palms. A mature, 
brown coloured, active root, growing at an angle of about 60° from the soil surface, was 
selected and prepared for root feeding. Only one root was selected for root feeding per 
palm assuming that all active roots were functioning equally well, and that a single active 
root is a representative sample. The root was severed with a smooth sharp cut and the cut 
end covered with moist cotton wool to prevent the entry of air bubbles. Immediately 
thereafter the root was inserted into a 1 % solution of LiCl, contained in a polythene bag. 
The polythene bag with the LiCl solution was tightly tied to the root in a manner that 
ensures the cut end is always immersed in the solution, even when the solution level falls 
due to uptake. 
Three days after root feeding, leaf, nut and root sampling was carried out. Root samples 
were collected from the fed roots, and from untreated roots on the opposite side to 
determine lateral movement within the root system. The amount of LiCl taken up by 
roots was calculated by measuring the amount left in the bags. Leaf samples were taken 
from the 3 r d , 6*, 9'\ 14*, 18 , h and 22* fronds, and nuts were taken from the 5'\ 8 , h and 12 , h 
bunches. Water of the harvested nuts was filtered using Whatman 42 filter paper, frozen 
at -20 °C and stored until the Li concentration was determined. Leaflets, without the mid 
rib, husks, cut into small pieces, and the root samples were dried at 80°C for three days 
and powdered using a Cyclotec (1093) plant sample grinder with 1 mm size sieve. 
Determination of Li 
Ten milliliters of defrosted nut water was used to determine Li in the nut water. For the 
analysis of Li in leaf, husk and roots, 1 g each of the powdered sample was used. Samples 
were measured into 250 ml conical flasks, and after adding 20 ml of deionized water they 
were shaken for two hours and filtered using Whatman 42 filter paper. Li content in the 
filtrate and in defrosted nut water was determined (Ranasinghe and Wijerathene, 2005) 
using an Atomic Absorption Spectrophotometer (Shimadzu AA-6200, Japan). The Li 
concentration in a particular organ indicates the amount of Li that has moved into it, 
along with water, from the treated root. 
Analysis of Data 
Data was analysed by ANOVA, using the GLM procedure of SAS. 
RESULTS 
Determination of Li in Roots 
In healthy, mild-LSD and moderate-LSD palms, the Li concentration in treated roots 
(10-13 ug/g) was significantly higher than in untreated roots (0.05-0.2 pg/g). The high Li 
concentration in the treated roots of both healthy and LSD palms indicates that the uptake 
of water is not obstructed when it is supplied directly to the roots. However, the low 
concentration of Li in untreated roots shows that the lateral movement of water within 
18 
the root system is restricted. In untreated roots, the highest concentration of Li was 
observed in mild-LSD palms (0.2 ug/g) while the lowest concentration in moderate-LSD 
palms (0.05 jig/g), whereas in the treated roots, the highest Li concentration was in 
moderate-LSD palms (12.56 ug/g), with appreciable concentrations in the mild-LSD 
(8.1 ug/g) and healthy palms (8.7 ug/g) (Fig 1). 
Untreated 
0.25 i 
0.2 
0.15 
0.1 
0.05 
o L. : 
Healthy Mid Moderate 
LSD disorder stages LSD disorder stages 
'
3
 Treated 
Figure 1: Li concentration in treated roots (la) and untreated roots ( lb) in healthy, 
mild-LSD and moderate-LSD palms, after root feeding with 1% LiCl. 
Determination of Li in nut water and husk 
Li content in the nut water and husk of healthy and LSD affected palms, was not 
significantly different in any of the maturity stages tested (5, 8 and 12 months old nuts). 
The pattern of Li transport to nuts in healthy and LSD palms was similar, with the highest 
Li concentration of 0.03 ug/g in the nut water of 5 month tender nuts), declining to 0.018-
0.02 jig/g in the 8 and 12 month nuts (Figure 2a). The inverse pattern was observed in the 
husk, with the lowest concentration of Li (0.015 ug/g) in the husk of 5 month nuts 
gradually increasing to 0.03 jig/g in 12 month nuts (Figure 2b). 
2a 2b 
0.04 0.04 
0.03 
002 
0.01 
5M 
| - x - Healthy -
8M mature 
Age of nuts 
- Mild —a— Moderate 
5M 8M mature 
Age of nuts 
I - Healthy - o - MKJ - A - Moderate 
Figure 2: Li concentration in the nut water (2a) and husk (2b) of nuts of different age 
(5M=5 months, 8M=8 months and mature=12 months), in healthy, mild-
LSD and moderate-LSD palms, after root feeding with 1 % LiCl 
19 
Determination of Li in leaves 
The Li content in the leaves of healthy and LSD-affected palms, was not significantly 
different in any of the fronds tested (3 r d , 6 t h, 9 t h, 14*, 18th and 22 n d fronds). The pattern of Li 
movement, and hence water movement to the fronds, was similar in healthy and LSD 
palms: a gradual increase up to the 14th frond and declining thereafter. In all the fronds 
tested, the lowest concentration of Li in all ages of fronds was in the moderate-LSD 
palms while the highest concentration was in the mild-LSD palms, an interesting feature 
that merits further investigation (Figure 3). 
0.12 
|> 0.08 
d 
c 
8 0.04 
, x -x ^ 
o 
_—-—X 
A 
3rd 6th 9th 14th 18th 22nd 
Frond 
—x— Healthy —o— mild —a— moderate 
Figure 3: Li concentration in fronds of different maturity, in healthy, mild-LSD and 
moderate-LSD palms, after root feeding with 1 % LiCl 
DISCUSSION 
The gradual increase of Li concentration up to 14 l h frond and decline thereafter shows that 
the pattern of water transport in leaves, as measured by Li concentration, is in keeping 
with their physiological maturity. The demand for water of the younger fronds in the 
canopy is greater as they are physiologically more active than the mature fronds. This 
pattern of water transport was common to healthy, mild-LSD and moderate-LSD palms, 
showing that the demand of individual fronds has a greater bearing than the LSD status of 
the palms. However, in terms of the quantity of water transported, the leaf Li 
concentration, in all the fronds tested, was consistently lower in the moderate-LSD palms 
than in healthy and mild-LSD palms. This is suggestive of obstructions to water 
movement in moderate-LSD palms. It appears that while there are no obstructions to 
water movement in mild-LSD palms, restrictions to water transportation could develop 
as the disorder condition increases in severity. 
20 
LI analysis shows that water movement into nut water behaves in a similar manner to that 
of fronds. The Li concentration in nut water is at a peak in the 5 month tender nuts and 
decreases in the nuts of the more mature bunch indicating a greater movement of water to 
the tender nuts. Li concentrations in the water of 5 month tender nuts were nearly 
identical in healthy, mild-LSD and moderate-LSD palms which indicates that water 
transport into the 5 month nuts was not affected by the disorder. However, the somewhat 
higher Li concentrations in the water of more mature nuts of healthy palms than in LSD-
affected palms suggests that water movement into the nut water of LSD palms is 
restricted. 
The very high Li concentration in treated roots compared to untreated roots shows that 
lateral movement of water within the root system is limited. In the untreated roots, Li 
concentration was relatively high in healthy and mild-LSD palms, and low in moderate-
LSD palms, which suggests that while water movement is not affected in healthy and 
mild-LSD palms it is restricted in moderate-LSD palms. The accumulation of Li in the 
treated roots of moderate-LSD palms also supports this contention. 
The results of this study show that the uptake of water by the roots, and the pattern of 
water movement from the root system to crown tissues are not affected by the LSD 
disorder. However, the quantum of water moved up to the fronds is restricted in 
moderate-LSD palms possibly due to the presence of obstructions. Restrictions in the 
root system may at least partially account for the reduced water movement to the crown 
tissues in moderate-LSD palms. Water movement in mild-LSD palms is free of 
restrictions. The higher stomatal diffusive resistance in moderate and severe LSD palms 
and the increasing internal water deficit with the increasing severity of the LSD disorder, 
observed by Ranasinghe, 2005, support the present findings. Further studies on water 
transport patterns at different heights along the trunk would provide interesting 
information. 
As Li is not a plant nutrient, plant tissues are not a sink for Li. Therefore, higher levels of 
Li in the tissues indicate that a greater amount of water has moved into the plant parts. 
Although the Li concentration in roots of healthy and mild-LSD palms, in this study was 
less than of moderate-LSD palms, it was still a considerably high level. In a similar 
experiment to study the water transport pattern in palms affected by Coconut Rapid 
Decline, the Li detected was very much lower in the healthy roots, and higher in the 
canopy level tissues than in the present study (Ranasinghe and Wijerathene, 2005). 
These differences indicate the need for more investigations on the fate of Li in plant 
tissues and use of Li in water transport studies in LSD-affected palms, including the 
reasons for retaining large amounts of Li in roots of healthy and mild-LSD palms. 
CONCLUSION 
Studies using Li as a tracer show that uptake of water into coconut roots, and the pattern 
of water movement from the roots to the crown tissues, are not influenced by the LSD 
disorder. However, in moderate-LSD palms water is retained in the roots, and the 
movement of water to the crown level is restricted. 
21 
ACKNOWLEDGEMENT 
The financial assistance received from the Council for Agricultural Research Policy 
(Grant No. 12/537/408) is gratefully acknowledged. 
R E F E R E N C E S 
Davis, T.A. (1962). Coconut Withering Disease of Ceylon. Coconut Research Institute 
of Sri Lanka Bulletin, No.22. Lunuwila, Sri Lanka, 
Ekanayake, U.B.M. (1964). Annual Report of the Crop Protection Division, Coconut 
Research Institute of Sri Lanka (1963). Ceylon Cocon. Quart. 15, pp 50-57. 
Fox, R.L. and Lipps, R.C. (1964). A comparision of stable strontium and 32P as tracers 
for estimating alfalfa root activity. Plant and Soil, 20,337-350. 
Jayasekara, C. and Premasiri, R.D.N. (1989). Report of the Plant Physiology Division. 
Annual Report of the Coconut Research Institute, Sri Lanka, 175-179. 
Lipps, R.C. Fox, R.L. and Kochier, E E . (1957). Characterizing root activity of alfalfa by 
radioactive tracer techniques. Soil Sci. 84:195-204. 
Madurapperuma, W.S., Ranasinghe, C.S., Mendis, H., Premasiri, N., Seram, A., 
Gunawardena, M., (1994). Application methods of Zn and the effect of macro 
and micro nutrient applications on the expression of leaf scorch decline 
symptoms in coconut (Cocos nucifera L) In: Proceedings II; International 
conference, 75 l h Anniversary, Coconut Research Institute of Sri Lanka. 237-247 
pp. 
Mahindapala, R.'and Chandrasena, A.M. (1975). Yield and drupe characteristics of 
coconut palms affected with Leaf Scorch Decline. Ceylon Coconut Quarterly 
26:73-76. 
Martin, M.P.L.D. Snaydon, R.W. and Drennan, D.S.H. (1982). Lithium as a non­
radioactive tracer for roots of intercropped species. Plant and Soil. 64,203-208. 
Nethsinghc, D.A. (1966). The application of isotopes in fertilizer research on the 
coconut palm. Ceylon Coconut Quart. 17:61-72. 
Pcrics, O.S. (1968). Studies on Leaf Scorch Decline of coconut palms. Ceylon Coconut 
Quarterly 3: 109-115. 
Rajapaksha, C.N.K. and Fernando, L.C.P. (1995). Leaf Scorch Decline of coconut in Sri 
Lanka in Proceedings on International .Workshop on Lethal Yellowing-like 
Diseases of Coconut, Ghana 5-9 November 1995., 97-104. 
22 
Ranasinghe C.S. and Wijerathene, A.J, (2005). Vegetative, reproductive and 
physiological changes in coconut palms affected by Coconut Rapid Decline. 
Cocos 17,01-10. 
Ranasinghe, C.S. (2005). Changes in the physiological performance of Leaf Scorch 
Decline (LSD) affected coconut (Cocos nucifera) palms. Experimental 
Agriculture 41 ,255-265. 
Ranasinghe, C.S., Wijesekara, R. and Wimalasekara,R. (2002). Rapid Decline 
Syndrome of Coconut (Cocos nucifera L.) - Preliminary report of a new 
condition. Palms 46:167-171. 
Vidanaarachchi, L and Nor, Y.M. (1994). Influence of palm oil sludge on physical 
properties of soil and growth characterization of oil palm seedling "Elaeis 
guineensis), Trop. Agric. (Trinidad) Vol. 71, No 2:95-99. 
2 3 


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National Science Foundation of Sri Lanka

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