Variation of karyotype formula, and asymmetry between individual plants of garlic and its relationship with ac transposon

الملخص EN

To study the karyotypic variation between the roots generated from cloves and bulbs within one genotype and among two different garlic accessions (Baladi and Egaseed1), the karyotype formula and asymmetry estimated from chromosome criteria (short arm, long arm, total length, centromeric index, arm ratio and relative length) were analyzed.

Almost all examined cells of the two studied genotypes showed 8 chromosome pairs (four large and four medium sized).

In Baladi genotype, four categories of karyotypic formula (8m, 7m+ 1sm, 6m+ 2sm and 5m+ 3sm) could be determined.

The former two (8m and 7m+ 1sm) were frequently predominant, while the other two categories (6m+ 2sm and 5m+ 3sm) were found in rare frequency.

Data showed variation in karyotypic formula among different cells of the same clove as well as among the different cloves of the same bulb.

Values of this parameter ranged from 52.22% to 58.26% and were evidently different among the three examined cells of the same clove as well as between the cloves and subsequently between bulbs of Baladi genotype.

However, Egasseed1 showed three categories of karyotypic formula (8m, 7m+ 1sm and 6m+ 2sm).

Karyotypic asymmetry indices of the examined cells in this genotype ranged from 54.91% to 58.64% .

In addition, the number of satellite (SAT) bearing chromosomes varied from zero to three chromosomes.

According to the existence and number of SAT chromosomes (chromosomes with secondary constrictions, SC) per genome of cloves and bulbs of the two studied genotypes, the examined cells have been divided into five forms (cells with zero, one, two, three or four SC chromosomes).

All five SC chromosome forms are found in cloves and bulbs of Baladi genotype but with different percentages.

Data also showed considerable differences of the percentages of these forms within and between cloves and bulbs of the two studied genotypes.

SC and SAT could be observed in all 8 chromosome pairs but with different numbers and distributions.

Data obtained after conventional PCR amplification of Ac transposable element clearly showed the existence of common monomorphic base fragment (100 bp) in all examined 18 cloves of the two studied garlic genotypes (Baladi and Egaseed1).

In addition, one polymorphic band of ~500 bp was detected in one clove from the first bulb and two cloves from the second bulb of Baladi genotype.

Likewise, this band (~500 bp) has appeared in two cloves from the first bulb of Egaseed 1 genotype.

The finding that there is additional 500 bp fragment of Ac transposable element in some cloves might be due to molecular relationship between autonomous and non-autonomous (truncated) transposition and may reflect the effect of transposition on chromosome structure and consequently on the karyotypic formula and asymmetry.