Asia’s rice production hit by ‘very aggressive’ weedy varieties, with up to 80% of harvest loss

As a result of the invasive weedy rice, harvest quality, yields and in turn market value of regular rice have declined significantly in recent years.

“They have become feral through a sort of accidental selection. They will eventually stick out over a crop field, but the problem is that by the time they are visible, there can often be quite an infestation,” Kenneth Olsen, Professor of Biology at Washington University, told This Week in Asia.

“A major weedy rice infestation can reduce crop harvests in a given field by over 80 per cent,” he said.

The origins of weedy rice are unclear, although farmers first reported its presence about two decades ago. A high proportion of its varieties in East Asia appears to be directly descended from hybrid rice varieties introduced in the 1980s, Olsen said. Other varieties of weedy rice have also crossbred with wild rice varieties in Asia.

“These very aggressive weedy forms can outcompete other rice crops [in terms of growth],” he said.

It only requires a small amount of weedy rice plants per square metre to cause huge damage to the harvest of cultivated rice, Olsen said. For instance, the US saw crop losses equivalent to an amount that was sufficient to feed 12 million people due to the damage caused by weedy rice in the last few years, he added.

Some of the weedy varieties are highly effective at dispersing their seeds in rice fields because of a certain genetic mutation.

“These seeds can lie dormant and be perfectly viable for 20 years,” Olsen said.

Major rice producer Thailand had reported losses of about 10 per cent of its output as a result of the weedy rice problem in recent years, said Tonapha Pusadee, one of the study’s co-authors.

Some studies show that weedy rice varieties found in