Authors: Anjali Soni, Preeti Singh and Jai Prakash
Division of Fruits and Horticultural Technology
ICAR-Indian Agricultural Research Institute, New Delhi-12
Correponding author email: singhjai2001@rediffmail.com
Papaya (Carrica papaya) is one of the most important horticultural crops of the country. India is the largest producer of papaya in the world. The major limiting factor in cultivation of papaya is its susceptibility to viral diseases e.g. papaya leaf curl (PalCV) particularly in northern parts of India.
History
Papaya has considerable economic importance to papaya industry in India. Papaya leaf curl disease was first reported in 1939 by Thomas and Krishnaswamy. This disease is of moderate incidence and widely distributed in India. Recent observations of papaya fields in India indicated that there has been a continued increase in the incidence of papaya leaf curl disease (as shown by symptoms), resulting in severe economic losses.
Symptoms
The disease is characterized by severe curling, mottling, crinkling and distortion of leaves, reduction of petioles, internodes and also the main shoot. The leaf margins roll downwards and from inverted cups. Affected leaves become leathery and brittle with twisted petiole and dark green thickened veins. The interveinal areas of affected leaves are raised on the upper surface due to uneven growth, hypertrophy, ruguosity and twisting of veins. The petioles are twisted in zig – zag manner and bend towards the main trunk. The early affected plants fail to flower and in case of occasional flowering, they bear few, small fruits. However, in late infection, fruiting is very less. In advance stages, dropping of fruits and defoliation takes place, the growth of plants is arrested and sometimes plant die.
Transmission
Papaya leaf curl virus is transmitted by vector but not by sap and mechanical means. In nature it is transmitted by the cotton whitefly ( Bemisia tabaci Gen.). Papaya is not a preferential host of whitefly. They show a mortality of 70 –80 per cent if forced to feed continuously on papaya for more than 24 hrs. Generally, more than 24 hrs are required for successful transmission of papaya leaf curl virus. Hence , it is assumed that the virus is acquired from alternate hosts such as tobacco, Zinnia and various weeds growing in and around papaya fields and transmitted to papaya in brief inoculation feeding.
Serology
Another sensitive method is the polymerase chain reaction (PCR) based amplification. Enzyme-linked immuno-sorbent assays (ELISA) and immuno-electron microscopes (IEM) are routinely used to detect the viruses of which ELISA is the most widely used method irrespective of the sample number. As the Papaya leaf curl virus is not mechanically transmissible, purification and production of antiserum is very difficult, which makes serological detection very difficult. Gemini viruses share lot of homology in their coat proteins, due to which detection of specific Gemini viruses by serological technique is not reliable
Host Range
The virus infects all the cultivars of papaya. It can also infect tomato, tobacco, Sunnhemp, chilli, Pitunia, Datura stramonium and Zinnia elegans. The virus also perpetuates on a number of hosts.
Management
- All the infected plants should be rogued out from the field as early as possible and buried or burnt.
- Use of granular systemic insecticides twice is also helpful in the management of this disease.
- The field should be kept weed free particularly during monsson season.
- Tobacco, tomato, sun hemp, Cape gooseberry, chilli,Pitunia, Datura stramonium, Zinnia elegans and Lantana camera etc. should not be grown near to papaya field.
- Growing of border crops/inter cops e.g. Maize, Bajara and Sorgham etc. to reduce the infestation of the vector pest.
- Use of sticky yellow trap to minimize the white fly population in field.
- Regular spraying of neem based pesticide e.g. Neemban or Neemagan (0.3%) at two weeks interval.
- Papaya nursery should be raised in net house or in isolated place free from white flies and should be sprayed with imidacloprid (0.03%) regularly at 21 days during July to September.
About Author / Additional Info:
I am a Senior Scientist at IARI New Delhi.