There is no cure for papaya ringspot disease and the disease is very difficult to control once it has become established. In home gardens within the biosecurity zones, infected plants should be removed as soon as symptoms are noticed.
Without biotechnology, “There's no papaya industry. Simple as that,†said Dennis Gonsalves, the scientist who developed the GMO papaya. The papaya ringspot virus nearly wiped the crop out. The virus first hit Hawaii in the 1940s and by the 1990s had reached almost every area that grows papaya.
Ring spot is caused by the fungus Mycosphaerella brassicicola. The disease is most severe during cool weather when heavy dews are present. The pathogen is disseminated within and among fields by windblown spores (conidia), and overwinters in infested crop debris.
Using the newly-invented technique of genetic modification, they used a genetic sequence from the virus and inserted it into the papaya genome. Analagous to vaccination in humans, this produced 100% virus-resistant plants. Activists invaded and damaged the papaya trials, and spread scare stories in the national media.
Rainbow is produced on 76% of Hawaiian papaya acreage, while SunUp is hardly grown commercially. SunUp is thought to be more resistant to exotic strains of PRSV, while Rainbow has shown susceptibility to such exotic strains of the virus.
In Hawaii and Taiwan, a mild strain of PRSV, HA5-1, has been used to protect papaya plants against the infection by virulent strains of the virus9. The first commercialized transgenic papaya carrying the PRSV CP gene was introduced to Hawaii in 1998 and saved the remains of the papaya industry10.
Maureen Fitch successfully developed an embryogenic calli system for papaya, and transformation was initiated with the gene gun from 1988 to 1989 (Fitch et al., 1990; Fitch and Manshardt, 1990, 1992).
The Rainbow papaya is an F-1 hybrid variety of papaya produced by crossing Hawaii's yellow-flesh Kapoho Solo variety with the red-flesh SunUp. A: Papaya ringspot virus is the most widespread and destructive virus disease of papaya.
Papaya Black Spot SymptomsBlack spot of papaya is caused by the fungus Asperisporium caricae, previously referred to as Cercospora caricae. This disease is most severe during rainy periods. Both the foliage and fruit of papaya may be infected with black spots.
It can be transmitted from plant to plant both mechanically by sap and by aphids in a stylet-borne fashion. It can also be transmitted in seeds and by the parasitic weeds, Cuscuta sp. (dodder).
The production remained high for two years following the discovery of PRSV in Puna due to massive efforts to control the spread of the virus. However, by 1995 papaya production in Puna had dropped to 39 million pounds and was down to 26 million pounds in 1998 when transgenic seeds of cultivars were released to farmers.
| Viral and viroid diseases |
|---|
| Mosaic | Papaya mosaic virus |
| Papaya ringspot | Papaya ringspot virus |
| Papaya lethal yellowing | Papaya lethal yellowing virus |
| Spotted wilt | Tomato spotted wilt virus |
Are squash and melons affected by mosaic virus safe to eat? “Yes,†says Nebraska Food Safety Educator Carol Larvick, citing information from Minnesota Extension. “These viruses are specific to plants and do not harm humans.
With a little tender loving care, Phalaenopsis orchids can often fight off infections or pests, but there is no cure for orchid viruses. You can try repotting a sick orchid; but if it continues to fail, you will have to discard it. Prevention is the best way to keep your orchid virus-free.
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. PRSV is the most serious threat to papaya production in the world [8].
Events Prior to the Survey. Papaya ringspot virus raised havoc on papaya farms from the time it first appeared in 1992 in Puna, Hawaii's major papaya-growing region, until 1998 when seed of Rainbow, a transgenic virus-resistant variety, were released to farmers.
The most effective fungicides for control are the protective fungicides containing chlorothalonil e.g., Daconil), copper sprays containing copper diammonia diacetate (e.g., Liquicop), propiconazole (e.g., Banner Maxx II), and the systemic fungicide thiophanate-methyl (e.g., Cleary's 3336, for professional use only).
