Genetic strategies to determine the mode of 2n egg formation in diploid potatoes

Abstract

In this study, nineteen diploid potato clones (Solanum spp . 2n = 2x = 24) were identified as 2n egg producers on the basis of fruit set in 2x-4x crosses . The segregation of three genes mapped close to the centromere, Got-1 (1 .1 cM), Pgm-2 (2 .0 cM), and Sdh-1 (8 .3 cM), were analyzed in the tetraploid offspring in these 2x-4x crosses to discriminate between First Division Restitution (FDR) and Second Division Restitution (SDR) modes of 2n egg formation . The co-dominant nature of these markers lead to more precise estimates of the recombinational frequencies as a result of completely classifying the segregating progenies . 2x-4x data revealed a predominance of SDR mechanisms occurring in 20 of the 21 families analyzed . With a SDR mode established, half-tetrad analysis (HTA) of four distal loci, 6-Pgdh-3, Mdh-1, Pgi-1, and Aps-1, revealed two SDR segregation patterns in some of the families . One pattern fit the expectations for the distal arm position . The gene-centromere map distances based upon SDR modes in the families following this pattern, were generally close to 4x-2x (FDR) estimates suggesting similar recombination rates between micro-and mega-sporogenesis . Heterozygosity transmission, on average, was 39 .1% . In the other segregation pattern, in which the diploid parents were derived from S. chacoense PI 230580, higher than expected homozygosity levels were found in the female 2n gametophyte populations . A post-meiotic doubling of the reduced megaspore, which generates homozygous 2n eggs, is suggested to operate in three families . The common genetic background of the diploid clones suggested a heritable nature of this mechanism . Pooled data from these three deviant families calculated that 1 .8% of the heterozygosity was transmitted to the tetraploid progeny .It is concluded that utilization of seven enzyme-coding loci, with previously established gene-centromere map distances, in 2x-4x crosses improved half-tetrad analysis (HTA) as a means to determine the mode of 2n gamete formation in megasporogenesis and megagametogenesis of diploid Solanum species.

Multilocus half-tetrad analysis and centromere mapping in citrus: evidence of SDR mechanism for 2n megagametophyte production and partial chiasma interference in mandarin cv ‘Fortune’

“…Analysis of the pattern of heterozygosity restitution within a linkage group is an alternative way to map the centromere compared with half-tetrad multilocus allelic configuration analysis Centromere mapping has been carried out in several crops (Douches and Quiros, 1988;Okagaki et al, 2008) and animals (Kauffman et al, 1995;Lindner et al, 2000), using HTA. In the present work, HTA has been carried out in two ways: by multilocus allelic conformation analysis, as described in Tavoletti et al (1996) and by comparison of observed and theoretical pattern of heterozygosity restitution rate within the linkage group under several models.…”

Estimation of the coefficient of double reduction in the cultivated tetraploid potato

“…The procedure regarding tissue processing, electrophoresis, staining, and non1enclature is described by Douches and Quiros (1988); however, a TRIs-borate buffer, pH 8.3 and gel system (Stuber et al 1988) was substituted for the TRIs-citrate buffer, pH 7.8. The MDH, PGI, 6-PGDH and IDH enzyme systems were resolved in the histidine-citrate, pH 5.7 buffer system, while the PRX and PGM enzyme staining was reserved for the TRIs-borate, pH 8.3 system.…”

“…Provided there is no selection associated with this process, the haploids express the gametophytic output of the parental tetraploids. Our ability to esti mate double reduction in potato has been enhanced because: (1) the process of extracting haploids has become routine using the haploid pollinator technique (Hougas and Peloquin 1958) and has resulted in large numbers of haploids (Kotch and Peloquin 1987), and (2) researchers have developed codominant potato isozyme loci with the resolution to detect allelic dosage within a tetraploid locus (Staub et al 1984;Martinez Zapater and Olivier 1984;Quiros and McHale 1985;Douches and Quiros 1988).…”

Postmeiotic restitution in 2n-egg formation of diploid potato

“…Through the use of appropriate meiotic mutants in potato, it has been possible to select genotypes that produce highly heterozygous FDR to relatively homozygous SDR populations of 2n-gametes (Ramanna, 1983;Werner & Peloquin, 1987;Werner et al, 1992;Douches & Quiros, 1988;Jongedijk et al, 1991;Bastiaanssen et al, 1996). It is believed that different meiotic aberrations can occur in one plant resulting in a mixture of FDR and SDR 2n-eggs (Conicella et al, 1991;Werner & Peloquin, 1991).…”

“…Previous investigations (Douches & Quiros, 1987, 1988Jongedijk et al, 1991;Werner et al, 1992;Barone et al, 1995) lacked segregation data for several loci on a single chromosome, preventing a detailed examination of the degree of heterozygosity, the restitution mechanism and the number of crossovers per chromosome in each individual 2n-egg. This also prevented firm conclusions on the exclusive occurrence of one restitution mechanism or a mixture of several restitution mechanisms in a genotype.…”