LORANTHUS -A PLANT PARASITE DECLINING MANDARIN IN NORTH EAST INDIA

~N. J. Singh,
~R. K. Avasthe, ~Raghavendra Singh, ~P. K. Pathak,
~B. Lepcha, ~P. Phukan, ~J. K. Singh, ~A. Gogoi

Loranthus is a common problem in most of the mandarin orchard in the North Eastern region. Loranthus, a dodder resembling cuscuta are the two major phanerogamic parasites of citrus in warm and humid regions. The parasites Loranthus is a glabrous shrub with green leaves but without a true root system. It produces long and tubler flower system in clusters. Birds and other animal disseminate seeds which can easily germinate on the branches and produce haustoria with which they get attached to the host. The nutrients derived from the host plant results in poor growth, low yield, less quality of fruit and finally leads to die-back and death of the host plant after 4-5 years of its infestation. Heavy infestation of this phanerogamic parasite was observed at Beyong village of East Sikkim growing beneath the bark of the Sikkim mandarin tree. Sikkim mandarin has wider impact as the source of their income generation in the village, hence matter is considered serious. Thus, the control measures of Loranthus spp. weed by removing the parasite in the early stages of its growth or by sawing it off from the branches of its host, so that the entire haustorial system is removed. This parasitic weed eradication is possible as community effort only as because it is transmitted by birds. Generally, birds consume seeds of Loranthus and it is transmitted within short time. Therefore, before flowering, it should be removed from the branches by pruning the branches. The pruning in nearby orchard should be done at a time when seeds of loranthus are unavailable for birds to transmit to other orchards.

Weed biology

Loranthus weed belongs to family Loranthaceae that contains stem parasitic plants that are commonly known as mistletoes. Most mistletoes are woody shrubs, often with brittle stem and leaves. Despite stem parasitic nature, their seedlings are photosynthetic, thus these plants cannot be considered holoparasites. It is a parasitic plant that derives some or all of its nutritional requirements from another living plant. They have special organs, named haustoria (singular: haustorium), which connect them to the conductive system of their host and provide them with the ability to extract water and nutrient from the host. After flowering and fruit set they disseminate the seed to other places through birds.

Mode of infestation

Loranthus is a genus of parasitic plants that grow on the branches of woody trees. Once established, it steals minerals and water, as well as block sunlight by covering the encroached place. The flowers of Loranthus are small, red colour and may be either unisexual or bisexual. The fruits are berries, usually containing a single seed. The parasite is found in dense cluster easily spotted o the branches of trees, bearing smooth broad leaves with tubular red flowers. The seeds are disseminated by birds from one plant to another. Seeds dropped on young branches of the host germinate and penetrate the tissue. The parasitic stem creeps along the branches of host and attaches with a peg like haustoria or knot like structures. Such structures were observed at the point of attachment as a bulged stem or knotty outgrowths on the stem of the host. It is phanerogamic parasite found mostly in the tropics rooting beneath the bark of the trees of mandarin cultivation infested with it. It derives the whole of its nutrients from sap of host plants i.e., mandarin resulting poor growth of the tree and low yield and quality of the fruit due to nutrients deprived from the host plant.

Mode of dispersion

After the infestation, the plant shows decline in growth and fruit yield and after three years if not controlled the plant shows declining symptom and finally the plant dies. It is a phanerogamic parasite found mostly in the tropics rooting beneath the bark of the trees.
Control Measures:
1. Prunning branches affected by Loranthus before it spreads to other branches of the tree is the best method of control. Affected branches of host plants should be periodically cut down before the flowering and fruit setting of this weed. It should be cut 10 cm below the infected part since the houstoria goes beyond upto 10 cm. the injured cut ends are pasted with Bordeaux mixture to prevent the entry of pests and diseases
2. High speed diesel will be helpful to kill the foliage of this parasitic weed.
3. Mechanical removal by hand when there is less infestation.

Mechanical removal of weed
Advisory services at farmers field

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Writers From Krishi Vigyan Kendra, ICAR-NOFRI, East Sikkim, Ranipool-737135, Sikkim, India. Phone no. 03592 251311; Email: kvk.eastsikkim@gmail.com. Corresponding email: johnson.singh1@gmail.com

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