The Queensland papaw industry could be under threat following reports that papaw seeds could spread papaya ringspot virus (PRSV).
This is based on the visit by two Queensland Department of Primary Industries (QDPI) researchers to the Philippines to discuss the results of research work conducted by Filippino scientist, Dr. Villegas. The work showed that papaw seeds may occasionally spread PRSV type p.
Queensland Fruit and Vegetable Growers are writing to the Minister for Primary, Industries, Simon Crean, to request that AQIS immediately impose a moratorium on the import of papaws from PRSV-infected countries until it is established whether or not the disease can be transmitted by seeds in the Australian papaw variety.
PRSV is a serious disease of papaws which can cause substantial losses in production and fruit quality. It was found in Australia for the first time in March, 1991, in the south east Queensland region.
Disease-infected plants are characterised by mottled yellow leaves and fruit which is covered with concentric rings and spots or c-shaped markings.
Dr. Villegas' research involved growing papaw plants from seeds that originated from PRSV-infected plants. "The experiments were apparently conducted in double-lined houses to prevent infection of the plants by insects," said Saleena Ham, horticulturist with Queensland Fruit and Vegetable Growers.
"The research was conducted to test a belief in the Philippines that PRSV is occasionally spread by seeds. Two seeds out of 1344 seeds (all derived from fruit of one infected tree) used in the experiment grew out with the infection."
The Australian Quarantine and Inspection Service (AQIS), previously has had no evidence that the disease may be spread by seeds.
"The understanding in Australia has been that it is carried through the sap of the plant, mainly by aphids," said Ms Ham.
"This is correct, however, Dr. Villegas's research has proven that it may also be spread by seed.
"The QDPI researchers who met with Dr. Villegas felt that her results were significant proof that seeds may spread the disease," said Ms Ham.
"In addition to this, a report has recently been released on a new device which is being used in the Philippines to screen seeds for PRSV. Known as the ELISA test, the device is a type of diagnostic kit, which treats papaw seeds as PRSV carriers. This report adds further weight to the assumption that PRSV is spread by seeds. The QDPI is now planning to repeat the experiment conducted in the Philippines to see if the Australian type of papaw plant will reveal the same results.
"The Australian type is the hermaphrodite variety. This type has both sexes combined in one plant. The filipino strain is the dioecious variety which does not combine two sexes in one plant. Therefore, there is a chance that results from the Australian experiment may differ from Dr. Villega's results," said Ms Ham.
However, if the results of the Australian research prove successful, it may be a step forward in preventing further import of the disease. To date, no further outbreaks of PRSV have been found in south east Queensland, but this situation is being carefully monitored by the QDPI.
DATE: March 1992
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