Seed companies are developing lettuce varieties resistant to Corky root disease, though progress is slow due to lab challenges. Some resistant varieties are now available for batavia, chestnut leaf, and pomelo types.
Corky root disease challenges lettuce growers
Corky root disease, caused by the soil-borne pathogen Rhizorhapis suberifaciens, is a significant problem for lettuce farmers. The disease affects plant roots, leading to reduced growth and yield, and is difficult to study in laboratory settings due to the pathogen's elusive nature.Seed companies develop intermediate resistance
Some seed companies have developed lettuce varieties with intermediate resistance to Corky root, but they may not widely publicize these traits. This is because identifying the cause of resistance in cultivation can be complex, slowing down the selection and release of resistant varieties.New resistant varieties for batavia lettuce
Batavia lettuce is one of the types for which resistant varieties are beginning to be offered, though options remain limited. Vilmorin-Mikado's Cortizone is the first batavia variety in France with Cork resistance, while Enza Zaden and Rijk Zwaan are also developing resistant varieties, with trials planned for 2027.Chestnut leaf lettuce has more resistant options
Chestnut leaf lettuce, both red and blonde, currently has the most resistant varieties available. Vilmorin-Mikado offers Eglantine and Bonemine, while Rijk Zwaan plans to introduce Bensaï in 2027. These varieties are designed to be planted in different seasons and regions.Blonde chestnut leaf lettuce options
For blonde chestnut leaf lettuce, Vilmorin-Mikado's Quator has been available for several years, with planting periods varying by region. Rijk Zwaan's Kiden is a newer addition, available for summer planting.Pomelo lettuce lags behind in resistance
Pomelo lettuce has fewer resistant varieties compared to chestnut leaf and batavia types. Vilmorin-Mikado leads in this area, offering Pavarotti as a resistant variety. Rijk Zwaan also has Abellina, which is resistant to Corky root and suitable for southern France.Combining resistances to multiple pathogens
Seed companies are also developing varieties that combine resistance to Corky root with resistance to two races of Fusarium, a fungal pathogen. Rijk Zwaan is working on a range of such varieties, including a red chestnut leaf and batavia with dual resistance, expected in 2027.Current resistant varieties with multiple resistances
Vilmorin-Mikado already offers several varieties with high resistance to Bremia and intermediate resistance to Fusarium. These include Abrivado, Charlestone, and Mascarpone. A red chestnut leaf variety with full Bremia and Fusarium resistance is also set to be added to their catalog in 2027.
