The US department of agriculture’s Agricultural Research Service (ARS) has developed seven new iceberg lettuce breeding lines with resistance to bacterial leaf spot (BLS).
The disease, which is caused by the pathogen Xanthomonas campestris pv. vitians, is an important disease of lettuce occurring sporadically in most major growing areas worldwide.
BLS thrives in wet, cool conditions and causes black spots to form on lettuce leaves. These black spots can merge and create papery, brown-to-black patches on the head. Upon harvest, growers must peel and discard the leaves to remove the patches, resulting in smaller heads that command less money.
BLS is difficult to prevent because the disease is highly dependent on weather conditions - growers could spray crops, but any application would have to be before symptoms developed, which is impractical. Because BLS is sporadic and unpredictable, these pre-emptive sprayings would be unnecessary in most seasons and lead to increased production costs. Therefore, according to ARS geneticist Ryan Hayes, creating disease-resistant breeding lines is the most efficient and cost-effective tool to manage BLS in lettuce.
Hayes, along with geneticist Edward Ryder (now retired) and plant pathologist Carolee Bull, developed the seven new breeding lines at the ARS Crop Improvement and Protection Research Unit in Salinas, in the centre of California’s salad belt. Between them they have worked for a decade on the project.
Similar in appearance to the famous Salinas variety created by Ryder, these lines are the first with commercially useful levels of resistance to BLS. ARS is providing these lines to seed companies, which in turn use them to develop new iceberg varieties for commercial use.
Hayes said: “These are not finished, named varieties yet, but the germplasm has been given to private seed companies and researchers and in five to 10 years, depending on their priorities, there will probably be commercial, named varieties.”
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