A team of scientists at the US department of agriculture’s Agricultural Research Service (ARS) has developed seven kinds of parent iceberg lettuce that resist corky root disease and attack by lettuce mosaic virus.
Plant geneticist Edward Ryder, now retired, and colleagues Ryan Hayes and Beiquan Mou at Salinas, California, developed the salads especially for California’s soils and conditions, which are similar to growing areas in parts of Spain.
Corky root causes lettuce roots to develop ugly, yellow-to-brown lesions that harden to a cork-like texture.
Infected plants may produce stunted heads 30-70 per cent smaller than normal. The bacteria Sphingomonas suberifaciens causes the disease.
The other headache, lettuce mosaic, results in stunted growth, as well as unattractive mottling of leaves.
Green peach aphids, about 25 millimetres long, can spread the virus from infected to uninfected plants as they move about a lettuce field, sipping plant juices.
These new lettuces have now joined the ranks of others developed at the agency’s research station in Salinas.
Breeding strong natural resistance into lettuce still prevails as the most economical way to defend the lettuce from disease-causing microbes.
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