Cytogenetic Analysis of Mehr Cotton Cultivar and Its Crossing Progenies: A Search for Unreduced Pollen Grains

Abstract

SummaryCotton is cultivated in Iran with diploid and tetraploid forms and hybridization is a means to increase the genetic diversity and obtain new elite cultivars in this crop. The present study considers cytogenetic study of the Mehr (Gossypium hirsutum) cotton cultivar and its crossing progenies. The cultivars showed bivalents, univalents and quadrivalents in metaphase of meiosis I. They differed significantly in mean values of chiasmata formation and chromosome pairing due to genetic difference. Different types of meiotic abnormalities like chromosome stickiness, laggard formation, micronucleus, tripolar and multipolar cell formation, cytomixis and unreduced pollen grain formation occurred in the parental genotypes and their hybrids. Grouping of the cultivars based on cytogenetic features showed the effect of parental genotypes on the meiotic behavior of their crossing progenies.Key words Hybrid cotton genotypes, Meiosis, Unreduced pollen grain.Cotton with its diploid (Gossypium herbaceum) and tetraploid (G. hirsutum) cultivars constitutes one of the most important crop plants of Iran cultivated in many regions of the country. Tetraploid cotton (Gossypium hirsutum) has a genome constitution of AADD (2n=52) (Menzel and Brown 1978) and is one of the worlds most dominant cotton cultivars.Hybridization is the main breeding strategy in cotton plants with the aim to broaden the genetic diversity available and produce new genotypes. Due to continuous artificial selection and cultivation of cotton cultivars, genetic erosion happens and useful genetic loci may be omitted from the germplasm. This could result in vulnerability to pests and diseases (Sheidai et al. 2008, Van Esbroeck andBowman 1998). Therefore, making new hybrid combinations and studying the amount of genetic diversity obtained is important.Our previous cytogenetic studies on cotton involved other cotton cultivars and they were mainly concerned with chiasma frequency and distribution (see for example, Sheidai et al. 2008, Tafvizi et al. 2010, Sheidai and Dezfolian 208, Sheidai et al. 2006, However the present report considers cytogenetic characteristics of the Mehr cultivar and its crossing progenies for the first time with special attention to unreduced (2n) gamete formation.

Assessment of Gene Flow BetweenGossypium hirsutumandG. herbaceum: Evidence of Unreduced Gametes in the Diploid Progenitor

“…Furthermore, Skovsted (1934), working on the production of hybrids between diploid Asiatic and tetraploid New World cotton, obtained a hybrid with 52 chromosomes, and hypothesized the production of 2 n gametes in the diploid parent. Likewise, in cytogenetic studies of cotton cultivars grown in Iran, the occurrence of large pollen grains was assumed to be potential unreduced gametes (Sheidai 2008; Noormohammadi et al 2012), although other methods are considered to be necessary to confirm the correlation between size and ploidy in pollen (Dewitte et al 2012). For the same type of sterile hybrids (triploids 2 n  = 39, one tetraploid 2 n  = 52) obtained by crossing A-genome Asiatic cottons with tetraploid New World cottons, Amin (1940) reported that backcrossing to New World cottons gave occasional success in boll setting on the F1s.…”