Zymogram patterns of alpha-amylase isozymes in Ethiopian tetraploid wheat landraces: insight into their evolutionary history and evidence for gene flow

The variation for alpha -amylase isozymes was analyzed in 71 tetraploid whe at (AABB genome) landraces from Ethiopia, including accessions of Triticum dicoccon Shrank, T. turgidum L., T. durum Desf., T. pyramidale Percival and T. aethiopicum Jakubz., by thin-layer polyacrylamide gel isoelectric focus ing. Four zymogram. phenotypes were obtained from all the materials studied . Except in T. dicoccon, however, the standard pattern of the durum wheat v ariety, LD222, was predominant. T. dicoccon showed two zymogram types that differed for the absence or consistently weak activity of band 18 (alpha -A my-B1) of the malt type. Band 1 (alpha -Amy-B3) of the malt type was fixed in T. dicoccon and present in only 10% of the free-threshing (FT) types. Ge nerally, the results indicated that the variation for alpha -amylase isozym es in cultivated tetraploid wheats, including landraces from secondary cent ers, is low possibly due to the founder effect or as a result of selection. The data were useful for inferences about the evolutionary history of Ethi opian wheat landraces. It is speculated that T. dicoccon was the first whea t to arrive in the Ethiopian highlands ca. 5000 years ago. However, it is n ot known whether the present day FT Ethiopian tetraploid wheat landraces ar e direct descendants of T. dicoccon, or whether they were introduced indepe ndently. The clear differences in alpha -amylase zymogram. patterns favor t he latter hypothesis. However, the presence of band 1 in some of the FT typ es indicated the occurrence of gene flow between the FT types and T. dicocc on, which may also explain the quantitative nature of spike threshability i n these landraces. Possible implications for durum wheat breeding are discu ssed.