A study by researchers from the National Institute of Agricultural Technology (INTA) and the National Council for Scientific and Technical Research (Conicet) has identified a virus causing the disease known as meleira, a significant threat to papaya production.

Viruses are the primary obstacle to global papaya production. Although more than 45 viruses have been reported in papayas across tropical and subtropical regions, only the Papaya Ringspot Virus (PRSV) and the virus causing meleira are considered threats to production.

“A few years ago, in connection with the development of fruit trees in northern Argentina and inquiries from local producers, we assessed plantations across provinces in both the northwest and northeast. We confirmed the presence of symptoms resembling those caused by viruses,” said Dariel Cabrera Mederos, a Conicet researcher at the Agricultural Phytopathology and Modeling Unit and the Plant Pathology Institute of INTA.

He added, “The visits were carried out with researchers and students from INTA research stations, Conicet, universities, technical schools, and technology validation centers that are part of the team.”

“These observations, along with the importance of this fruit for regional producers, prompted us to begin research on the subject,” confirmed Cabrera Mederos.

Papaya, also known as mamón, ranks fourth among tropical fruits produced globally.

In Argentina, it is primarily grown in subtropical provinces such as Salta, Jujuy, Chaco, Corrientes, Formosa, and Misiones, where more than 300 producers are based. Due to its economic benefits, mainly tied to market value and industry uses, the planted area has expanded over the past decade.

During regional tours, researchers observed disease symptoms, such as mosaic patterns on leaves, similar to those caused by viruses, but inconsistent with previously reported viruses.

Cabrera Mederos noted that samples underwent various analyses, revealing association with a new potexvirus, previously unreported globally, called papaya virus X.

Papaya virus X is transmitted mechanically on papaya and is present in most inspected areas in Salta and Jujuy.

Evaluations conducted in Corrientes, Salta, and Jujuy beginning in 2021 showed papaya plants with latex exudation on fruits.

He explained that “molecular analysis of these samples suggested the presence of a virus associated with meleira, one of the most devastating diseases in papaya worldwide. Subsequently, genetic analysis confirmed the presence of a new virus.”

How to Identify It and What to Do

PRSV causes mosaics, leaf deformation, and ring patterns on fruits. Papaya virus X induces intense mosaic patterns on leaves without affecting the fruit.

In the case of meleira, spontaneous latex exudation occurs on fruits, which oxidizes and produces characteristic symptoms. The high incidence and severity of symptoms observed in the field suggest potential crop yield impacts.

“Although we have not conducted direct studies on yield impact, we know the incidence reaches 100% in the first year, complicating the handling and washing of fruits intended for sale,” said Cabrera Mederos. Additionally, “the rapid spread of this disease has hindered the establishment of new plantations.”

In Brazil, meleira’s damage to papaya has led to complete plantation destruction as a proposed management measure to prevent disease spread.

Preliminary research results confirmed the virus's mechanical transmission, suggesting disinfecting tools used for field sanitation, especially when entering new plantations.

“Furthermore, we propose preventive management, from cultivation planning and nursery stages to plantation management, such as avoiding proximity to affected lots, using barrier plants, and frequently disinfecting and monitoring crops,” Cabrera Mederos said.

Currently, studies on these diseases are ongoing to provide official information to Senasa and propose effective management measures for producers.

Photo courtesy of INTA