What was it all about?

This investment, which ran from 2018 to 2022, worked towards the development of new testing protocols and the delivery of clean material to help protect the papaya industry against papaya sticky disease.

Papaya sticky disease has been identified in Australia. Plants infected with the disease have fruit that exudes a watery latex which dries on the skin, producing unmarketable fruit. In Australia, the disease is caused by a seed-transmissible virus (PMeV2-Aus) and has only recently been discovered, with very little known about it. -

The project had three main objectives; to develop a clean seed testing protocol targeting the causal agent(s) of papaya sticky disease, to generate clean seed for lines and varieties of importance to industry, and to undertake activities to improve knowledge of papaya sticky disease in Australia.

Clean seed testing protocol

A robust testing methodology has been developed and validated to routinely diagnose plant infection with PMeV2‑Aus, the causal agent of sticky disease in Australia. This test can be used for diagnostics of any strain currently identified in Australia. This test, and the slower more generic test can be accessed by industry through Grow Help, the Department of Agriculture and Fisheries fee-for-service pathology service.

Generation of virus free parental material

Ten parent lines testing clean from PMeV2-Aus have been delivered to industry. These lines were chosen as a priority by industry for production of current hybrids. Representatives of these plants have been entered into tissue culture for long term maintenance. Papaya Seeds Australia, the commercial seed production for Australian Industry, have been informed of methods for production of virus free seed with respect to the current knowledge of virus epidemiology. If recommendations are followed, clean seed will soon be available to growers.

Knowledge development of papaya sticky disease

The project has demonstrated that there is only a single, encapsulated virus involved in the papaya sticky disease in Australia, in contrast to the situation in Brazil and elsewhere. The properties of the Australian strain of the virus appear to be different to what is reported elsewhere, or there are assumptions being made about PMeV2.

The rapid movement of virus into clean planting material indicates an aerial insect vector. The lack of uninfected plant material has limited the amount of epidemiology that could be performed on the PMeV2‑Aus so far. The multiplication of clean parent material by tissue culture can allow this work to begin.

Current knowledge of the virus involved in sticky disease and project progress has been disseminated to growers both through the industry communication circular ‘Papaya Press’, and grower meetings throughout the term of the project.  

ACT NOW

Further information about Papaya Leaf Diseases can be found on the Queensland Government Department of Agriculture and Fisheries website.

Read this Papaya Clean Seed Update published in Papaya Press magazine, May 2020, page 5.

Information is also available from this Papaya sticky disease: biosecurity alert published on the WA Department of Primary Industries and Regional Development website in July 2022.