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 (Carica papaya) is most important member of the family Caricaceae. It is commercially grown throughout the tropical and subtropical region of the World. However, Viruses are important limiting factor for the successful cultivation of papaya throughout the world and nowadays worldwide Papaya ring spot virus (PRSV)is most destructive disease to hinder commercial cultivation.
History
Hawaiian papaya production has been severely affected by PRSV. The virus was introduced to Oahu as early as 1937, then moved to the Puna region of Hawaii Island and dropped 94% Production. The virus emerged in commercial farms in 1992 and by 1995 production in Puna was impossible. At the end of the decade Hawaiian papaya production was halved.
Taxonomy
PRSVis an aphid-transmitted plant virus belonging to the genus Potyvirus, family Potyviridae. The PRSV is divided into two major biotypes or strains based on their host range. The PRSV-W type affects cucurbits but not papaya while the PRSV-P type affects papaya and cucurbits.
Hosts
PRSV has a limited number of hosts belonging to the families Caricaceae, Chenopodiaceae and Cucurbitaceae.Transmission
The virus is naturally transmitted via aphids in a non-persistent manner, means it does not enter beyond the feeding mouthparts of the aphid, and does not circulate or multiply within its insect host. Non-persistent viruses are transmitted quickly and easily between plants. Many species of aphid can transmit PRSV, particularly the Peach Aphid and Melon Aphid. Disease transmission can also occur by planting infected seedlings in fields where the virus is not present, and is typically not seed-transmitted.Symptoms
Symptoms of PRSV manifest as a prominent mosaic pattern on the leaf lamina, wet-oily streaks on the petioles and upper part of the trunk, and the distortion of young leaves.The virus cause deformation and ringspot symptoms on the fruits, hence it was named PRSV.
PRSV Management
Any single approach will not be capable to manage PRSV disease, therefore integrated measures have been recommended i.e. quarantine and geographic displacement, roguing and netting, cross-protection, and genetic modification of the host plant.
1. Quarantine
Restriction on the movement of infected plants in new area known as quarantine. This method can delay the spread of disease but not usually provide long term control.
2. Geographic displacement
Geographic displacement of cropland is common and has occurred in Hawaii, the Philippines and Brazil. When fields become infected, such as the case of Oahu papaya growers, attempts to relocate growing areas to virus-free fields are made. This is usually just a temporary avoidance of the disease, which eventually spreads to the new fields.
3. Roguing
The removal and destruction of infected plants, is a way to control the spread of PRSV. This method was employed unsuccessfully when PRSV began to invade the Puna region of Hawaii. It is difficult to suppress the spread of PRSV through rouging because it is spread very quickly and effectively by aphids.
4. Netting
It can also be used to prevent insect vectors from spreading the virus. Production under netting is prohibitively expensive for subsistence and small-scale producers, but was used effectively in Taiwan because geographical displacement was not possible on such a small island.
5. Resistant Species
The various species of vasconcella is reported to have resistance to PRSV: Vasconcella cundinamarencis,Vasconcella cauliflora, Vasconcella quercifolia and Vasconcella stipulata.
6. Cross protection
A mild strain of PRSV is introduced into the host plant, which then develops resistance to virulent strains of the virus. In Hawaii mild strains were isolated after a virulent strain of PRSV HA was treated with nitrous acid is PRSV HA 5-1.This mild strain virus has been commercially used in Hawaii and Taiwan since 1985.
7. Transgenics
There are two transgenic varieties of papaya; Rainbow and SunUp, with engineered resistance to PRSV have been commercially grown in Hawaii since 1998.
About Author / Additional Info:
I am a Senior Scientist at ICAR-IARI, New Delhi.