Maize is known to be susceptible to drought stress, which negatively affects vegetative growth and biomass production, as well as the formation of reproductive organs and yield parameters. In this study, 27 responsive traits of germination (G) and seedlings growth were evaluated for 40 accessions of the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) germplasm collection, under no stress and simulated drought stress treatments by 10%, 15%, and 20% of polyethylene glycol (PEG). The three treatments significantly reduced G% and retarded seedlings growth, particularly the 15% and 20% PEG treatments; these two treatments also resulted in a significant increase of abnormal seedlings (AS). The heritability (H2) and correlations of the traits were estimated, and drought tolerance indices (DTIs) were calculated for traits and accessions. The H2 of G% values were reduced, and H2 for AS% increased as the PEG stress increased. Positive correlations were found between most trait pairs, particularly shoot and root traits, with 48 highly significant correlations under no stress and 25 highly significant correlations under the 10% PEG treatments, particularly for shoot and root traits. The medium to high heritability of shoot and root seedling traits provides a sound basis for further genetic analyses. PCA analysis clearly grouped accessions with high DTIs together and the accessions with low DTIs together, indicating that the DTI indicates the stress tolerance level of maize germplasm. However, the resemblance in DTI values does not clearly reflect the origin or taxonomic assignments to subspecies and varieties of the examined accessions.

SummaryThis study aimed at investigating the changes imposed by gamma radiation in mitotic activities and the chromosomes as well as the vegetative criteria and yield of M1 and M2 plants of five cowpea cultivars. Seeds of cultivars (Kaha 1, Dokki 331, Azmerly, Cream 7 and Giza 6) were exposed to levels of γ-radiation ranging from 50 to 300 Gy. Low levels of γ-radiation enhanced mitotic activity and resulted in significant increase in chromosomal abnormalities in the root tip cells of M1 and M2 plants. The percentage of abnormalities varied among the varieties and was generally lower in M2 plants compared to M1 plants. The 50-Gy and 100-Gy doses of γ-radiation induced positive effects on plant growth and yield of M1 plants, while the 300 Gy of γ-radiation caused detrimental damage on three cultivars (Dokki 331, Azmerly and Cream 7), which failed to grow to flowering. More pronounced improvements in growth and yield were recorded in M2 plants; the increase in growth and yield was often associated with increased mitotic activity and the occurrence of chromosomal abnormalities, indicating that γ-radiation-induced chromosomal abnormalities are not likely to be associated with negative effects on growth or yield. Based on the calculated yield index, 50 Gy of γ-radiation may be used to improve the yield of three varieties (Dokki 331, Azmerly and Cream 7) and the 100 Gy dose may be recommended for improving the yield of the two varieties, Kaha 1 and Giza 6.

The origin and ancestry for Egyptian clover, Trifolium alexandrinum, was examined using AFLP data. The data support a close relationship of T. alexandrinum accessions from Syria and Egypt to T. apertum, T. berytheum, and T. salmoneum. However, crossability and geographic distributions suggest that T. apertum is an unlikely progenitor. In contrast, T. salmoneum appears to be the most probable progenitor for Syrian material of Egyptian clover, although a close relationship to T. berytheum was also revealed. The ability of these species to cross freely indicates that T. salmoneum and T. berytheum may be regarded as the primary ancestors from, which man domesticated Egyptian clover through artificial selection in Syria. Following domestication, the earlier forms of the crop species could have been taken into rain-fed cultivation in Palestine and irrigated cultivation in Egypt. In this regard, the domestication of Egyptian clover may be analogous to other crops, such as barley and wheat, which were also domesticated in the Fertile Crescent and taken into cultivation in the Nile Valley. It appears that genetic improvement of the crop occurred in Egypt after cultivation, and that the varieties that were developed in Egypt were later distributed worldwide.

Knowledge of the origin and domestication history of crop plants is important for studies aiming at avoiding the erosion of genetic resources due to the loss of ecotypes and landraces and habitats and increased urbanization. Such knowledge also strengthens the capacity of modern farming system to develop and scale-up the domestication of high value potential crops that can be achieved by improving the knowledge that help to identify and select high value plant species within their locality, identify and apply the most appropriate propagation techniques for improving crops and integrate improved crop species into the farming systems. The study of domestication history and ancestry provide means for germplasm preservation through establishment of gene banks, largely as seed collections, and preservation of natural habitats. Information about crop evolution and specifically on patterns of genetic change generated by evolution prior, during, and after domestication, is important to develop sound genetic conservation programs of genetic resources of crop plants and also increases the efficiency of breeding programs. In recent years, molecular approaches have contributed to our understanding of the aspects of plant evolution and crops domestication. In this article, aspects of crops domestication are outlined and the role of molecular data in elucidating the ancestry and domestication of crop plants are outlined. Particular emphasis is given to the contribution of molecular approaches to the origin and domestication history of barley and the origin and ancestry of the Egyptian clover.

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