People should dispose of papaya seeds properly if they are uncertain about the sources of the plant they are from, organic farmers advise.
They say proper disposal is vital to control the proliferation of genetically modified papaya trees and minimise the risk of contamination.
'Many people love papaya and sometimes they like to plant their own with the seeds left from the fruit. But they might release more GM papayas unknowingly,' Fan Ling grower Augustine Lo Yat-man said.
Contamination occurs when the pollen of a male GM papaya is carried to the flower of a female non-GM plant by insects or the wind.
Scientists said this cross-pollination would not alter the plant itself or create genetically modified fruit, but the seeds could be changed. Trees grown from these seeds and their fruit would contain modified genes.
To avoid contamination, natural papaya plants should be planted with a buffer area between them and modified trees. Generally a kilometre is enough as bees seldom travel further. But this is difficult in Hong Kong where farms are so close together.
Distinguishing GM from non-GM papaya is difficult, if not impossible. Farmers cannot find out if their papaya are contaminated without a laboratory test costing HK$1,000.
Lo feels public education is equally important, so he attaches a note to his produce reminding consumers not to replant the seeds.
But some farmers are taking a more ambitious approach. They are introducing a scheme to replace papaya trees, regardless of their status, with GM-free ones.
Under the scheme, more than 600 trees have been switched at four villages in the New Territories, and 400 more will be replaced before winter.
'Hong Kong is such a small place and it is much easier than the mainland or other places to get rid of them,' said Vicky Lau Yuen-yee, from Green Farm, who helps contact farmers to make the switch.
But Professor Jonathan Wong Woon-chung, from Organic Resource Centre, said the switch's impact would be limited. 'No matter what you do, the risks will not be totally eradicated,' he said.
He advises farmers to replace their trees every one or two years and plant only seeds certified as GM-free. 'This will ensure the first-generation fruits will be GM-free but for future generations the risks remain,' he said.