In another move to cope with soaring vegetable imports, domestic seed makers have begun curbing exports of vegetable seeds that return to Japan as produce, officials of the Japan Seed Trade Association said Tuesday.

The voluntary export curb, a first for seed makers, follows criticisms from Liberal Democratic Party lawmakers and others that the rapid growth of vegetable imports is partially due to seed exports.

Domestic seed producers annually sell about 69 million tons of seeds, of which 94 percent goes to the Japanese market. The rest is exported by Japanese trading houses and other businesses. Later, some of the green peppers, eggplant, watermelon and other produce from the seeds is exported to Japan.

The voluntary curb, which the officials said is to promote domestic cultivation of vegetables, comes on top of emergency restrictions imposed April 23 on imports -- mainly from China -- of stone leeks, shiitake mushrooms and rushes used in tatami mats.

Japan has also slowed quarantine inspections of vegetables since April, ostensibly to prevent the entry of crop-damaging insects.