Today's commercially grown romaine is vulnerable to what's known as lettuce dieback disease. The disorder, which can easily devastate entire fields of this popular lettuce, is caused by one or more soil-dwelling Tombusviridae viruses.

Two Agricultural Research Service plant geneticists have now bred what are apparently the first parent romaine lettuces that are resistant to these pernicious plant viruses. Edward J. Ryder and colleague Rebecca C. Grube developed the three novel lettuces, known as 01-778M, 01-781M and 01-789M, at the agency's U.S. Agricultural Research Station in Salinas, Calif.

These lettuces result from about three years of research and testing in both infested and disease-free fields at Salinas and two other coastal California sites. The scientists noted that the lettuces have not yet been tested in other regions of California or Arizona where romaine lettuce is grown.

Small supplies of the seeds of the new lettuces are available to plant researchers and breeders.