Karyotype Analysis Of Acacia Senegal Var. Senegal

Abstract

Hashab tree (Acacia senegal) is an important species for its environmental and economical benefits like Gum Arabic production. Gum Arabic yield varies considerably between individual trees, which may be due to variation in karyotype. The aim of this study was to karyotype Hashab trees in terms of chromosomes number, length, symmetry index and centromere position. Seeds were obtained from Kordofan States. They were treated with hot water and placed in damp filter paper at temperature between 22 to 25 Cº for germination. Roots tips were collected after three days in the morning and midday and two pretreatments of colchicine and potassium chloride applied before fixation. They were prepared for microscopic examination by squash and permanent methods. The results showed that roots collected at midday showed active mitotic divisions compared to those collected in the morning. Also, pretreatment with potassium Chloride resulted in full spread of the chromosomes better than colchicines. The karyotype showed the number of chromosomes was 26 chromosomes (2n = 2x =26) while only one cell showed possible tetraploidy (52 chromosomes). The chromosomes were ranked from 1 to 13 according to the total length that varies from 2.80 μm to 5.41μm. According to the centromere position, the haploid set of the chromosomes was classified as one median, three slightly sub median, seven sub median and two highly sub median. The symmetry index and total formula were 0.51 and 43.75% respectively, indicating the symmetry of A. senegal genome