Argentinian agricultural organizations have identified a virus that…

Researchers from the National Institute of Agricultural Technology (INTA) and the National Council for Scientific and Technical Research (Conicet) have discovered a virus responsible for meleira, a serious threat to papaya production.

Viruses pose the greatest challenge to papaya cultivation worldwide. While over 45 viruses have been identified in papaya plants across tropical and subtropical areas, only the Papaya Ringspot Virus (PRSV) and the virus responsible for meleira currently pose a significant risk to production.

“A few years ago, in response to the development of fruit trees in northern Argentina and inquiries from local farmers, we evaluated plantations in the northwest and northeast. We identified symptoms similar to those caused by viruses,” stated Dariel Cabrera Mederos, a researcher at Conicet's Agricultural Phytopathology and Modeling Unit and the Plant Pathology Institute of INTA.

He remarked, “These evaluations involved researchers and students from INTA research stations, Conicet, universities, technical schools, and technology validation centers, working together as part of the research team.”

“The observed symptoms, along with the significance of this fruit for local producers, motivated us to investigate further,” Cabrera Mederos confirmed.

Papaya, also known as mamón, is the fourth most produced tropical fruit globally.

In Argentina, it is mainly cultivated in subtropical provinces like Salta, Jujuy, Chaco, Corrientes, Formosa, and Misiones, where over 300 producers operate. Due to its economic potential, largely due to market demand and industrial uses, the area under cultivation has grown in the last decade.

During field visits, researchers noted disease symptoms, such as mosaic patterns on leaves that were not consistent with previously identified viruses.

Cabrera Mederos indicated that samples taken underwent several analyses, which revealed a connection to a new potexvirus, previously unreported worldwide, known as papaya virus X.

This new virus is mechanically transmitted and has been found in most areas inspected in Salta and Jujuy.

Assessments conducted in Corrientes, Salta, and Jujuy since 2021 revealed papaya plants exuding latex from their fruits.

Mederos explained, “Molecular analysis of these samples indicated the presence of a virus linked to meleira, one of the most destructive diseases affecting papaya globally. Genetic analysis later verified the presence of this new virus.”

Identification and Management

PRSV typically causes mosaic patterns, leaf deformation, and ring patterns on fruit, while papaya virus X results in intense mosaic patterns on leaves without impacting the fruit.

In the case of meleira, fruits exhibit spontaneous latex exudation, which oxidizes and leads to distinctive symptoms. The high rate and severity of symptoms in the field indicate potential reductions in crop yields.

“While we have yet to conduct direct yield impact studies, we know that the incidence can reach 100% in the initial year, complicating the handling and washing of fruits intended for sale,” Cabrera Mederos noted. Furthermore, “the rapid spread of this disease complicates the establishment of new plantations.”

In Brazil, meleira has caused total destruction of papaya plantations as a preventive measure against disease transmission.

Preliminary findings confirm the virus’s mechanical transmission, suggesting the need for sterilizing tools used during field sanitation, especially when entering new plantations.

“Additionally, we recommend preventive management measures, ranging from careful planning during cultivation and nursery stages to plantation management practices. This includes avoiding proximity to infected areas, using barrier plants, and regularly disinfecting and monitoring crops,” Cabrera Mederos advised.

Ongoing research into these diseases aims to provide official information to Senasa and propose effective management strategies for producers.

Photo courtesy of INTA