Improving the health of coconut trees through the management of root (wilt) disease

Introduction

Coconut palm (Cocos nucifera L.), a versatile tree crop with multifarious uses is important for the livelihood of millions of people in India. It is affected by more than 50 diseases in different parts of the world. Among the various diseases, the root (wilt) disease caused by phytoplasma and fungus is a major disease and it affects various plantation crops viz., coconut, arecanut, date palm, oil palm etc. Root wilt disease in coconut caused by an obligate Phytoplasma, is a serious problem in most of the coconut plantations of Kerala and currently fast spreading and becoming serious production constraint in many of the districts of Tamil Nadu. The pathogen is highly pleomorphic and reside endocellularly in insects and phloem tissues of coconut palms. The pathogen is spread by insect vectors and further no resistant varieties are available for this pathogen. The principal diagnostic symptom of the disease is flaccidity (ribbing) of middle whorl leaves followed by yellowing and marginal necrosis of leaflets in the older leaves. The spindle in RWD affected palm is weak, where softening and whitening of leaflets are invariably seen. It is a systemic disease, caused by phytoplasma. The pathogen is transmitted by insect vectors such as lace bug -Stephanitis typica and plant hopper -Proutista moesta (Solomon et al., 1999) [1] . The RWD is non-lethal but causes a slow decline (debilitating) and the disease generally spreads slowly. The RWD has come to stay in eight southern districts of Kerala state. The disease is also noticed in isolated pockets in northern districts of Kerala and sporadically in Theni, Dindigul, Kanyakumari, Thenkasi and Coimbatore Districts in Tamil Nadu bordering Kerala. The currently available chemical method by controlling the insect vectors is less effective. In order to prevent the further spread of the disease in the state, the present proposal on 'Safeguarding coconut plantations in Tamil Nadu from Root Wilt disease -A farmer participatory programme' is proposed. The infection of pathogen on palms results in the total loss to the farmer. The spread of root wilt in coconut can be reduced only by removal of the infected palms. Despite decades of research, a complete control for phytoplasma is not yet available, but measures were made to reduce its rate of spread. Under the project, root (wilt) disease was identified some areas and to study the spreading pattern of the disease. Integrated Disease Management strategies including cultural, chemical and biological methods for root (wilt) in coconut in hot spot areas under farmer's holding will be developed and also needs to be disseminated through large scale demonstrations in farmer holdings. The outcome of the project will generate the best method for root (wilt) management/maintenance for field level adoption to the coconut farmers on Tamil Nadu. One of the significant features of the root (wilt) disease is that it is not lethal but a debilitating malady which responds to ideal management practices.

Materials and Methods

Observation on root (wilt) disease index will be recorded and the percentage of disease index will be worked out. The difference between the pre-treatment and post-treatment observations will give the reduction in disease severity. In order to save time, scoring can be restricted to the leaves in any of the five spirals (Pillai et al, 1999). The major foliar symptoms associated with the root (wilt) disease of coconut are flaccidity, yellowing and necrosis. Disease index will be calculated to quantify the disease intensity, by adding the weighted average grade points of the different symptoms in all the leaves of a palm.

D.I = ∑ ( 𝐹 + 𝑌 + 𝑁 ) × 10 𝐿

where F -Grade points assigned to flaccidity (0-5) Y -Yellowing (0-3) N -Necrosis (0-2) L -Total number of leaves Disease index can vary from '0' to '100" where '0' represents the total absence of all the symptoms and '100' means the presence of all the symptoms in the acute stage on all the leaves. Disease Index below 20 -Early stage Disease Index 20 to 50 -Middle stage Disease Index above 50 -Advanced stage (Radha et al., 1972) [2] Results and Discussion The treatments were imposed as the technical programme and the observation recorded on root wilt incidence using the formula as furnished below.

Where the grade points assigned to F-Flaccidity (0-5) Y-Yellowing (0-3)

Sum (F+Y+N)

Disease Index = X 10 L N-Necrosis (0-2) L is the total number of leaves Roving survey was carried out during 2023 to 2024 to assess the incidence of root (wilt) in different villages of Coimbatore, Tirupur, Dindigul, Theni, Thenkasi, Tirunelveli and Kanyakumari districts. The highest root wilt index of 54.63 and 54.42 Kuruthencode and Killiyoor blocks, Kanyakumari District followed by 43.41 per cent was recorded in Anaimalai block, Coimbatore District (Table 2). Pre treatment and post treatment observation (one year after application) were recorded in the trial plot. The results of the experiment conducted at Alankadavu revealed that the soil application of recommended dose of fertilizers + soil application (SA) of microbial consortia @ 200 g (Trichoderma asperellum (Tv 1 ) and Bacillus subtilis (Bbv 57) each at 100 g + FYM @ 50 kg + Neem cake-5 kg + Green manuring + Providing drainage channels + TNAU Cococon @ 2 litres / palm (at bimonthly interval) should be applied (Two times at six months intervals) (T 2 ) recorded the lowest percent disease index (30.04 PDI) followed by T 1 (31.27 PDI) of root wilt disease against farmers practise (T 3 ) 34.79 PDI respectively (Table .3).

Srinivasan (1999) [3] reported some of the management strategies which include; application of balanced fertilizers, control of leaf rot disease, application of farm yard manure, provision for drainage, growing green manure crops, raising intercrops and removal of disease affected palms. Srinivasan et al. (2010) [4] reported that, the soil application of Pseudomonas fluorescens, Bacillus subtilis and Trichoderma viride in coconut palms to manage root (wilt) associated leaf rot symptoms in field conditions. Ramjegatheh et al (2012) [5] reported good management practices in the RWD in coconut palms it can reduced the disease incidence.

Conclusion

Roving survey was carried out during 2023 to 2024 to assess the incidence of root (wilt) in different villages of Coimbatore, Tirupur, Dindigul, Theni, Thenkasi, Tirunelveli and Kanyakumari districts. The highest root wilt index of 54.63 and 54.42 Kuruthencode and Killiyoor blocks, Kanyakumari District followed by 43.41 per cent was recorded in Anaimalai block, Coimbatore District. Soil applica-tion of recommended dose of fertilizers + soil application (SA) of microbial consortia @ 200 g (Trichoderma asperellum (Tv 1 ) and Bacillus subtilis (Bbv 57) each at 100 g + FYM @ 50 kg + Neem cake-5 kg + Green manuring + Providing drainage channels + TNAU Cococon @ 2 litre / palm (at bimonthly interval) should be applied (Two times at six months intervals) was effective in reducing the root (wilt) incidence. The awareness programmes were conducted further trickle down to other farmers through the participants of these programmes.

Acknowledgement

AcknowledgementThe authors are thankful to the Coconut Research Station, Aliyarnagar, Tamil Nadu for providing assistance during the research programme.

References

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2. Radha K, Lal SB. Diagnostic symptoms of root (wilt) disease of coconut. Indian J Agric Sci. 1972;42:410-413.
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