Chromosome Pairing and Chiasma Formation in Some Olive (Olea europaea L.) Cultivars of Iran

Abstract

Summary Cytogenetic characteristics of 11 olive cultivars were studied considering their chromosome pairing and segregation. The cultivars studied possessed 2nϭ4xϭ46 chromosome number and formed only bivalents in metaphase of meiosis-I. The cultivars differed significantly in their chiasma frequency and distribution as well as chromosome pairing indicating partly their genetic distinctness. Meiotic abnormalities including laggard chromosomes and chromosome stickiness occurred in the cultivars studied. B-chromosomes, cytomixis and unreduced pollen grains were observed in some of the cultivars. Clustering and ordination of the olive cultivars based on cytogenetic characteristics showed distinctness of these cultivars. B-chromosomes and unreduced pollen grain formation are new in olive cytogenetics.Key words B-chromosome, Cytogenetics, Cytomixis, Olive.The olive-tree (Olea europaea L.) is one of the most characteristic species of the Mediterranean area and nowadays is the only cultivated representative of the genus Olea. Since its chromosome complement is 46, it is considered-although not demonstrated-a tetraploid species by Brousse (1987), while according to Green and Wickens (1989) olive is a diploid species, comprising the cultivated type (var. sativa) and the wild type sylvestris (syn. Olea oleaster Hoffm. et Link). Cultivated olives are propagated vegetatively while wild olives only reproduced by sexual mean. These two olive types are interfertile (Zohary and Spiegel-Roy 1975).Olea europaea is the only cultivated representative of the genus Olea, having about 2600 different cultivars cultivated in different regions of the world. Since the beginning of its domestication, olive has been propagated vegetatively to exploit the best combination of genes which arose by random crosses or mutations (Carriero et al. 2002). As a result, a great number of varieties are present in all the countries where this species is cultivated, raising several problems for germplasm management and preservation. Evaluation and characterization of olive genetic resources is therefore crucial.In general very little work is available about olive cytogenetics (Bitonti et al. 1999, Minelli et al. 2000 and as a result of shortage of knowledge on the olive genome, there is controversy about olive phylogeny and its relationship to its related wild forms (Zohary 1994, Bitonti et al. 1999.Olive cultivars are grown in different parts of Iran and cultivation of the same cultivars for long period of time may lead to the genetic erosion confining the subsequent breeding programs. Therefore it is necessary to study the available diversity and introduce new variability as well. For this reason, the present study considers cytogenetic study of 11 olive cultivars available in Iran, considering the chromosome pairing and segregation, the occurrence of B-chromosomes and cytogenetic abnormalities for the first time.

Species Relationships in Hordeum: Cytology and RAPD Analyses

“…Young flower buds were collected from 10 randomly selected plants of each species/population and fixed in glacial acetic acid : ethanol (1 : 3) for 24 h. Flower buds were washed and preserved in 70% ethanol at 4°C until used (Sheidai et al 2008). Cytological preparations used squash technique and 2% aceto-orcein.…”

“…For grouping of the species a combined data set was produced from meiotic data obtained in this study and karyotype data reported before (Sheidai and Rashid 2007). Since the species studied differed in their chromosome number, relative cytological data were used, for this purpose, mean of ring and rod bivalents per cell, mean of univalents per cell and total chiasmata per bivalent were used (Sheidai et al 2008).…”

“…Since the species studied differed in their chromosome number, relative cytological data were used, for this purpose, mean of ring and rod bivalents per cell, mean of univalents per cell and total chiasmata per bivalent were used (Sheidai et al 2008). Similarly karyotype features not affected by the chromosome number, including size of the longest and shortest chromosomes, total form percentage (TF%) and A1 and A2 karyotype indices of Romero-Zarco (Sheidai and Rashid 2007) were used. Cluster analysis using Unweighted Paired Group with Arithmetic Average (UPGMA) and Neighbor Joining (NJ) methods was performed on relative cytological characteristics.…”

“…Extensive cytological studies have been carried out in the genus Hordeum mainly concerned with chromosome number and polyploidy level (Bothmer 1979, Bothmer et al 1986a, b, 1987, Zhang et al 1990, Jahan et al 1992, Bothmer et al 1995, Bao-Rong 1997, Sheidai et al 2008. The study of the meiotic behaviour of interspecific hybrids suggested the existence of 4 basic genomes of H, I, X and Y in the genus (Bachmann 1998).…”

“…Parsa (1950), Mobayyen (1981) and Bor (1970) reported the occurrence of 11 Hordeum species in Iran; however the species recognition is varied by these authors. Our previous cytogenetic study of the genus contained karyotype analysis of some species (Sheidai and Rashid 2007), while the present study considers chiasma frequency and chromosome pairing in 6 populations of 4 species as well as RAPD analysis of 10 species of Iran.…”