MSc

Kerala the ‘Land of coconut’ occupies first position in area and production
of coconut in India but the productivity is below the national average. This is
because of unproductive and senile palms, lack of adaptation of recommended
cultivation practises and serious incidence of pests and diseases. The root (wilt),
an endemic disease of Kerala causes an annual loss of 968 million nuts. Recently
another type of yellowing characterised by mid whorl yellowing shedding of
immature nuts and drying of inflorescence without showing characteristic ribbing
symptom is rapidly spreading in many parts of Kerala. There is no research report
available in this emerging problem in the coconut growing tracts of Kerala. Since
there is rampant spreading of yellowing to other coconut cultivated areas causing
a serious reduction in nut yield, this problem demands immediate attention. Hence
an experiment was conducted in the Department of Plant Physiology, College of
Agriculture, Vellyani to generate the basic information on the causative agents
and on the changes of physiological, molecular and anatomical realms of coconut
affected by mid whorl yellowing.
A wide variation was observed in the physiological parameters like total
pigments, relative water content, carbohydrate fractions, proteins, phenols and
antioxidants betweenpalms with yellowing and control palms. The palms with
yellowing showed a significant reduction in the total chlorophyll, chlorophyll a,
chlorophyll b and carotenoid content when compared to the healthy palm.
Relative water content was lower for all the palms with yellowing compared to
the control palm and the healthy palms were maintaining a better water status and
membrane integrity. All the selected palms with yellowing recorded an
accumulation of reducing sugars compared to the healthy palms. The trend was
similar for starch content except for palms with general yellowing. The control
palms recorded maximum protein content compared to other palms with
yellowing. A significant increase in the phenolic compounds was observed in
palms with yellowing compared to the healthy palms. This results point to an
activated defense system. The 14th leaf starting from the first fully opened one is
the most widely used leaf for nutrient analysis as recommended by the IRHO.
(Fremond et al., 1966).The 14th leaf data from the control palms and palms with
different types of yellowing were analysed. The data showed that there were
significant reductions in the levels of major nutrient nitrogen, phosphorus and also
in the levels of magnesium and the micronutrient manganese in case of palms
showing mid whorl yellowing compared to the control palm. But significantly
higher levels of accumulation were found in case of potassium, calcium, iron and
copper. These variations in the nutrient levels can have an influence on symptom
development in coconut palms. The maximum yield was recorded for the control
palm. Chlorophyll degradation and loss of structural integrity were evident from
the anatomical studies of leaf tissues in case of palms with yellowing. Vascular
browning which extended to the cortex and the vascular disintegration in the roots
of affected palms were seen on anatomical analyses.
A pure quality DNA was obtained by modified CTAB DNA isolation
protocol. Molecular analyses using nested PCR showed that with the phytoplasma
specific universal primers P1/P7-R16F2n/R16R2 provided an amplicon ) in the
positive control and palms with inner and middle whorl yellowing and the
primers R16mF2 /R16mR1 -R16F2n/ R16R2 provided an amplicon for the
positive control and palms with inner, middle and general yellowing. The root
(wilt) phytoplasma specific semi- nested primers IF7/7R3- IF7/7R2 provided an
amplicon of 493 bp only for the positive control and no amplification was seen in
any of the selected palms. The control palm and the palms affected with outer
whorl yellowing provided no amplification at all for any of the primers tested.
Amplification of phytoplasma specific universal primers in palms with mid whorl
yellowing indicates that phytoplasma has got a role in development of the specific
symptom. This demands immediate attention and extensive studies on the
etiology, changes in biochemical profile, anatomy etc.
Salient Findings
Amplification of phytoplasma specific universal primers in palms with
mid whorl yellowing indicates that phytoplasma has got a role in development of
the mid whorl yellowing symptom. But in case of the root (wilt) phytoplasma
specific primers, there was no amplification in palms with mid whorl yellowing.
This suggests that the mid whorl yellowing of coconut palm which is an emerging
problem in Kerala may not be associated with the root (wilt) disease.
The results of biochemical and physiological analyses of the selected
palms clearly indicate an altered primary metabolism, source-sink relation and a
complexity in the nutriophysiology. These altered conditions can act as
predisposing factors for the development of specific symptoms.
The anatomical analyses showed damages of roots in the palms with mid
whorl yellowing. They will have internal browning of vascular elements,
extending into the cortex and also disintegration of vascular elements.
Future line of work
Detailed analysis of nutriophysiology, source-sink relation and hormonal profile.
Studies on soil factors like nutrient level and water status.
Extension of anatomical studies to different type of tissues.
Extension of molecular studies into identification of specific phytoplasmal strains
associated with mid whorl yellowing of coconut palms.
Development of management strategy for the improvement of the field
performance and productivity of coconut palms with mid whorl yellowing.