Diseases 113
10.1.2 Management
Papaya is not a preferred host of the PRSV vectors and aphids. Disease management
by controlling the vector within the papaya orchard is very difficult as aphids visit
and probe papayas but do not colonise papaya orchards. Papaya plants infected with
PRSV must be destroyed in order to minimise spread of the virus. Virus problems
can be avoided by planting genetically resistant cultivars. PRSV is not transmitted
via seeds, but it can be spread to areas where it is not present by transporting infected
seedlings. To avoid introductions of the virus, do not transport diseased papaya seed-
lings to different areas. In areas where PRSV is already present, raise seedlings in
nurseries close to the planting site to maximise the possibility of spreading the viruses
further. Early detection of infected plants and prompt removal can check the further
spread of the disease. The various options for managing viral diseases are vector
control, planting in areas where there is no virus, roguing, netting, cross protection
and resistance (Tripathi et al. 2008; Gonsalves et al. 2010). Aphids can be controlled
by application of Carbofuran (1.0 kg a.i./ha) at the time of sowing seeds, followed by
2–3 foliar sprays of dimethoate or phosphamidon (0.05%) at an interval of 10 days
starting from 15–20 days after sowing (NHB 2002). As mentioned above, the eco-
nomically relevant host range of PRSV includes papaya and cucurbits, two crops that
are very different in growth characteristics. PRS-resistant genetically engineered
papaya lines have been designed like, 55-1 and 63-2 using virus coat protein. Papaya
ringspot potyvirus gene (CaMV 35S uidA) leader sequence was identified at Hawaii.
These transgenics were produced by biolistic (particle bombardment) transformation
of embryogenic cultures of the papaya cultivar, ‘Sunset’, with DNA-coated tungsten
particles. Papaya lines, 55-1 and 63-1, were used to create the cultivars, SunUp and
FIGURE 10.2 (See colour insert.) Mosaic symptoms on papaya plant.