Sporophytic-gametophytic herbicide tolerance in sugarbeet.

In vitro selection procedures for herbicide tolerance were initially developed in the sporophytic generation of sugarbeet (Beta vulgaris L.), and then tested in the gametophytic generation. The primary objective of our study was to develop and evaluate in vitro techniques for identifying genotypes within heterogeneous seedling populations tolerant to specific herbicides, and to use meristematic cloning procedures to synthesize clones genetically tolerant to the herbicide. Seed from cloned selections tolerant to the herbicide ethofumesate were obtained and compared to plants from seed of the original population (using germination, central bud development, and root dry weight). Verification for in vitro selection accuracy was accomplished by pollen germination studies in the gametophyte. The results indicate that in vitro selection of germinated seedlings in the presence of the proper concentration of challenging agent can be effective in identifying genotypes tolerant to ethofumesate. Such identification was accomplished in fully differentiated tissue, but without the necessity of mature plants. Gametophytic studies, via pollen germination, indicated an association between genes operating in the sprophyte and those in the gametophyte. Cloning the seedlings identified as tolerant genotypes, and subsequent intercrossing of these clones provided a convenient method of synthesizing populations with gene frequencies shifted in the direction desired.