Research on the inheritance of fasciation in lettuce (Lactuca sativa L.)

Summary Inheritance of fasciation was investigated in reciprocal crosses between two lettuce varieties: Suzan (non-fasciated) and Noran (fasciated). In glasshouses parental plants, F₁, F₂, and F₃ populations were assessed for fasciation according to a scale from 0 (non-fasciated)-9 (extremely fasciated).The observed environmental variation for fasciation of the homozygous parents was very low or absent, but the environmental variation for the F₁ populations was large. On the basis of this large variation of the heterozygous F₁ plants we supposed that such a variation also occurred in F₂ and F₃ populations.Considerable mortality was observed in all generations, which supposedly occurred at random in parents and F₁ but was non-random in the segregating F₂ and F₃ populations. So, means and variances of F₂ populations will be biased and therefore they were not used for genetical analyses of fasciation.From F₁ and F₃ populations and from some F₂ populations it appeared that no differences occurred between reciprocals. The differences for fasciation between reciprocal F₂ populations in the 1977 A experiment may result from non-random plant survival. A regression of F₃-means on the values for fasciation of parental F₂ plants, adjusted for their inbreeding, resulted in a realized h²-narrow of 0.4. This indicates that in the surviving plants of the F₂ populations still additive genetic variation was present to select successfully for non-fasciated plants.