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Ongoing project

Papaya clean seed program (PP18001)

Key research provider: The Queensland Department of Agriculture and Fisheries

What’s it all about?

Beginning in late 2018, this investment is tasked with delivering a clean seed protocol to help protect the papaya industry against papaya sticky disease.

Papaya meleira virus 2 (PMeV2) is a seed-transmissible virus that is associated with symptom development in papaya sticky disease. Investigations have found the virus in plant lines used to generate seeds for the industry, raising the need for a clean seed program.

The work is also investigating other causal agents of the disease and raising general awareness.

This update first appeared in the November 2020 edition of the Papaya press which is produced by the Papaya industry communications program (PP16001).

Delivered by research provider, Department of Agriculture and Fisheries Queensland (QDAF), the ‘Papaya clean seed program’ (PP18001) is working to better protect the papaya industry from papaya sticky disease by delivering a clean seed protocol. Lead researcher, Dr Paul Campbell, has provided the following update.

Testing for the final three parent lines from Papaya Seeds Australia have recently been initiated through the embryo rescue program to clean up the papaya meleira virus. Though it will be a while before they are large enough to test for the virus.

Similar to results from the first two parent lines, the project team hope to see very low numbers of infected plants after the embryo rescue. So far, they’ve identified only five infected plants from the embryo rescued material, with most plants having been tested several times.

The project team have been working with Papaya Seeds Australia to move virus free plants into the field to establish reinfection rates and monitor for the presence of the virus. This is critical in the development of a management plan for parental lines to ensure virus free seed for industry.

Clean plants from the previous seven parent lines have all been established in tissue culture to safeguard industry’s investment towards clean seed. Over eighty plants from six parental lines have been planted in the field at both the Tablelands and on the coast.

Plants are being regularly sampled and tested for papaya meleira virus, to evaluate virus movement in the field. The speed of the reinfection will have a large impact on the management of the parent material to produce clean seed moving forward.

The project team at QDAF have also been working on developing a new type of test to support the virus diagnostics. This new test seeks to identify if a plant is infected within 45 minutes directly from a drop of latex
from the fruit. No special equipment will be required, the reaction will just need to be kept at a constant 65°C.

In the future this kind of test could be used directly by industry to check on the infection of the plants. Further work is being done to explore the availability of tests to diagnose infection directly from a small amount of leaf tissue.

This update first appeared in the May 2020 edition of the Papaya press which is produced by the Papaya industry communications program (PP16001).

Delivered by research provider, Department of Agriculture and Fisheries Queensland (QDAF), the ‘Papaya clean seed program’ (PP18001) is working to better protect the papaya industry from papaya sticky disease by delivering a clean seed protocol. Lead researcher, Dr Paul Campbell, has provided the following update on the virus transmission studies conducted to test virus free plants.

The production of parent lines free of the virus that causes papaya sticky disease continues to move forward, with the plants of seven parent lines being tested under the embryo rescue system and over 200 virus free plants currently in an insect proof screen house.

The numbers of infected plants continue to be low, with only five plants testing positive for the virus from the embryo rescue material. These materials are currently being established in tissue culture to assess long-term maintenance of the virus free lines.

It’s vital that we undergo this monitoring and testing for the creation of lines for the seed industry into the future. Currently, the project team are working with Papaya Seeds Australia to move some of the virus free plants into the field to establish reinfection rates.

The plants will be monitored for the presence of the virus over the next year to see how quickly they get infected by the virus, which will provide information vital to developing the management plan of parental lines to ensure virus free seed for industry.

With access to virus free material, the project team have begun working on characterising the virus to better understand how it is spread and how soon it can be detected post-infection. None of this basic knowledge is presently available and will be critical for future management decisions.

This update first appeared in the November 2019 edition of the Papaya press which is produced by the Papaya industry communications program (PP16001).

Delivered by research provider the Department of Agriculture and Fisheries Queensland (DAF), the Papaya clean seed program (PP18001) works to deliver a clean seed protocol to help better protect the papaya industry against papaya sticky disease. DAF researcher on the project, Dr Paul Campbell, provided a quick update on the progress towards improving understanding of the disease, and management options for future seed production processes.

The first plantlets produced under the clean seed project have tested negative to the virus PMeV2 Aus that causes papaya sticky disease. Initial stages of the project have focused on four parental lines, including the parents of the popular red variety RB1. The plants were produced through embryo rescue and tissue culture, and when planted out, they were protected in insect proof caging to stop the virus coming in from outside. The initial lines put through this system had ~98 % virus‑free plants. 

The transmission of viruses by seed is never one hundred percent. Even if the seed is infected, the embryo inside the seed may not be, but the process of germination infects the seedling. By using embryo rescue, we eliminate that infection mechanism and increase the chances of getting clean planting material. Dr Chat Kanchana-Udomkan (Griffith University), has done a great job getting the embryo rescue system established for the different parent lines. Finding the right seed age for embryo rescue is critical to the success of the technique.

Next steps for the project are to establish tissue culture lines for long term protection of the clean mother plant lines and get more parent lines through the system. We will also be starting some basic virus transmission studies now that there are some virus free plants available.

Related levy funds
Details

This project is a strategic levy investment in the Hort Innovation Papaya Fund.