The increasing demand of organically produced lettuce can only be met by enlarging the assortment and stabilizing the yield. Cultivating lettuce of a high quality safely
requires varieties with improved stress tolerance, a well-developed ability to utilize nutrients, a low demand of water, as well as a high resistance to pathogens,
particularly to downy mildew. Planting mixtures might be seen as an alternative method to present pure varieties. The results of four-year studies in the field in three
locations showed that line mixtures reacted in a far more stable way to stress factors than pure varieties. The diversity in cultures is promoted by mixing so that the
variation of resistance can be exploited to control diseases. Total losses caused by Bremia lactucae like in pure varieties did not occur. The homogeneity of mixtures in
the habitus is sufficient for direct marketing and retail
