Pre- and post-fertilization barriers to backcrossing the interspecific hybrid between Allium fistulosum L. and A. cepa L. with A. cepa

Abstract

To facilitate the introgression of desirable traits of Allium fistulosum into the genome of A . cepa, several accessions of the hybrid between these species were pollinated with A . cepa as the recurrent parent, and in vitro ovary and ovule culture were performed to obtain an increase in the recovery of backcross progeny . Compared to the results obtained from seed development in planta, the increase in the number of backcross progeny was generally very limited, and in some cases even a decrease was found . Raising the sucrose concentration in the ovary culture medium resulted in a higher frequency of ovules developing back seed coats but this was not followed by an increase in the number of backcross progeny obtained . Pollen tube growth of A . cepa was disturbed in the styles of the interspecific hybrids . Per ovule, frequencies of micropylar penetration exceeded frequencies of backcross progeny only to a limited extent . Hence, it was concluded that in the tested interspecific hybrid accessions the attainable gain in viable backcross progeny by the application of in vitro culture techniques is limited by strong pre-fertilization barriers acting at the level of stylar incongruity.

Meiotic Irregularities in Interspecific Crosses Within Edible Alliums

“…Pre-fertilization barriers in distant crosses, such as failure in pollen germination, slow pollen tube growth, or foreign pollen tube arrest in the style have been reported in different species (Kiełkowska & Adamus, 2006;Manickam & Sarkar, 1999b) including alliums (Gonzalez & Ford-Lloyd, 1987;Ohsumi et al, 1993;van der Valk et al, 1991a). Postfertilization barriers are related to abnormalities in the development of the zygote, absence or abnormal development of the endosperm which causes embryo starvation and abortion (Zenkteller, 1990).…”

“…Cytological studies showed reproductive abnormalities in F1 hybrids and their progenies. Irregularities of chromosome pairing and occurrence of a range of structural changes in meiotic chromosomes resulted in unbalanced chromosome complements in the gametes, often causing lowered fertility or even sterility of the F 1 hybrids (Khush & Brar, 1992;Peffley, 1986;van der Valk et al, 1991a).…”

“…Hence, hybrids between onion and A. fistulosum as well as several backcross progenies were deeply studied, with A. cepa as either the female parent (Emsweller & H.A. Jones, 1935a, 1935bLevan, 1941;Van der Meer and Van Benekom, 1978) or pollen parent (Peffley, 1986;Peters et al, 1984;van der Valk et al 1991a). Cytological studies have shown that chromosome pairing is highly variable in the F 1 hybrid depending on the parental combination (Emsweller & H.A.…”

“…Levan's (1941) attempts to backcross (BC) F 1 hybrid A. cepa x A. fistulosum to cepa were unsuccessful. The studies of van der Valk et al (1991a) showed that difficulties in this type of cross were due to pre-fertilization barrier, as the growth of onion pollen tubes in the style of the hybrid was disturbed. Maeda (1937) backcrossed F 1 to A. fistulosum and obtained viable seeds.…”

Hybridization and Molecular Characterization of F1 Allium Cepa × Allium Roylei Plants

“…Unfortunately, subsequent backcrosses of the obtained F 1 A. cepa × A. fistulosum hybrids to A. cepa have proved problematic. The difficulties observed in genome transmission in advanced backcross generations have been explained by the sterility of F 1 A. cepa × A. fistulosum hybrids probably resulting from one of three possible mechanisms: stylar incongruity (van der Valk et al, 1991a), nuclear cytoplasmic incompatibility (Ulloa et al, 1995) or central cell nuclear cytoplasmic incongruity (Mangum and Peffley, 2005). Due to problems in introgression of Japanese bunching onion traits into onion, so far only four new varieties of A. fistulosum have been developed: Beltsville Bunching, Delta Giant, Top Onion and Wakegi Onion (Kik, 2002).…”