Page 188 - FRUTAS DEL TRÓPICO

188 Frutas del trópico

Bunchy top is transmitted by two leafhoppers, Empoasca papayae and E. stevensi, and
distribution of the disease largely coincides with their distribution (Ploetz et al., 1994; Ploetz,

2003). The former is the principal vector, and is the only leafhopper known to breed on pa-

paya. Single insects of both species can transmit the agent with symptoms appearing 30 to

45 days after inoculation. The level of tolerance in a cultivar affects the rate and severity of

symptom expression. Tolerant cultivars are useful where disease pressure is low. Control has

been achieved by applying persistent insecticides for vector control and topping affected plants

to allow development of healthy axillary shoots (Cook, 1972). Antibiotic therapies through

drenching and root tip treatments have resulted in remission of symptoms.

Papaya ringspot. Papaya ringspot, caused by the non-persistent, aphid-borne potyvirus Pa-
paya ringspot virus, is the most widespread and destructive disease of papaya (Ploetzet al., 1994;

Ploetz, 2003). Plants of all ages are susceptible and symptoms are generally more severe during

cooler weather. The disease derives its name from the characteristic dark-green sunken rings that

develop on petioles and fruit of affected plants that often persist as dark orange to brown mar-

kings as fruit mature. Dark-green, water-soaked streaks develop on petioles and stems. Mottle

and mosaic patterns of varying severity develop on leaves that often have a ruffled appearance.

Affected plants become stunted and fruit set is markedly reduced or absent (Cook, 1972.
Papaya is the major primary and secondary source of inoculum, and rapid secondary

spread can occur with plantations (100% incidence in < 6 months) (Ploetz et al., 1994;

Ploetz, 2003). Transmission is almost entirely due to transitory aphid populations as papaya is

not a preferred host and aphid colonies are very rarely found on plants.

Quarantines and rouging can delay the spread of the disease but do not usually provide

long-term control. Establishing plantations with pathogen-free seedlings is essential, and new

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