Cytological and breeding behavior of pentaploids derived from 3x × 4x crosses in potato

Abstract

Cytology and breeding behavior of Solanum commersonii - S. tuberosum hybrids derived from 3 x x 4 x crosses was examined. The chromosome number of hybrids ranged from hypo-pentaploid (2 n=5 x - 8=52), to hyper-pentaploid (2 n=5 x + 7=67), with the euploid pentaploid 2 n=5 x=60 class predominant. The high variability in chromosome number of the 3 x x 4 x hybrids was attributed to the fact that meiotic restitution during megasporogenesis of the 3 x female may have involved poles with various chromosome numbers, resulting in 2 n eggs with 24-48 chromosomes. Microsporogenesis analyses provided evidence that chromosome pairing between S. commersonii and S. tuberosum genomes occurred. In addition, chromosome distribution at anaphase I and anaphase II revealed an average chromosome number of 29.5 and 29.1 per pole, respectively. To further study the extent of transmission of extra genome chromosomes from pentaploids, 5 x x 4 x and 4 x x 5 x crosses were performed, and the chromosome number of resulting progeny was determined. Ploidy ranged from 2 n=4 x=48 to 2 n=5 x=60 following 5 x x 4 x crosses, and from 2 n=4 x + 1=49 to 2 n=5 x=60 following 4 x x 5 x crosses. These results provided indirect evidence that the pentaploid hybrids produced viable aneuploid gametes with a chromosome number ranging from 24 to 36. They also demonstrated that gametes with large numbers of extra chromosomes can be functional, resulting in sporophytes between the 4 x and 5 x ploidy level. Fertility parameters of crosses involving various (aneuploid) pentaploid genotypes were not influenced by chromosome number, suggesting a buffering effect of polyploidy on aneuploidy. The possibility of successfully using (aneuploid) pentaploid genotypes for further breeding efforts is discussed.

Pairing analysis and in situ Hybridisation reveal autopolyploid-like behaviour in Solanum commersonii × S. tuberosum (potato) interspecific hybrids

“…Homoeologous pairing was also observed in PMC from the BC 1 and BC 2 progenies, showing mostly multivalents (16 on average in the BC 1 and 13 in the BC 2 ) with relatively few bivalents and very few univalents. It appears to be higher than that observed by Barone et al (1999) and Carputo (2003). Put together, our chromosome pairing evidence indicates that the F 1 triploid hybrids between S. commersonii and S. tuberosum Group Phureja behave as autotriploids and that homoeologous recombination can take place among all their chromosomes.…”

“…In our case BC 1 plants were aneuploid, while Barone et al (1999) found that most were exact allopentaploids. The cases of 5x-aneuploids were explained in terms of occasional omission of chromosomes in the restitution nuclei forming 2n eggs (Carputo 2003). The most important post-zygotic barrier in potatoes is EBN.…”

Pólen 2n e mecanismos meióticos de formação em Solanum commersonii ssp

“…e S. commersonii subsp. malmeanum Bitt., que possuem alelos de resistência a baixas temperaturas, resistência à murcha bacteriana causada por Ralstonia solanacearum e à podridão mole e canela preta causadas por Erwinia carotovora, além de apresentar um alto teor de matéria seca (CARPUTO, 2003;ROCHA et al, 2000).…”

Resistance to Frost and Tuber Soft Rot in Near-Pentaploid Solanum tuberosum-S. commersonii Hybrids

“…The strategy was based on doubling the chromosome number of CMM, and on the production of 3x(2EBN) bridges derived from 4x × 2x crosses between 4x(2EBN) CMM and 2x(2EBN) genotypes. Since the triploids produced 2n eggs, they could be used in 3x × 4x crosses with TBR to obtain (near)pentaploid bridges displaying a high level of aneuploidy (Carputo 2003). The unique ploidy of the genotypes produced made this material suitable for broadening our understanding of the cytological, genetic and reproductive behavior of genotypes with odd ploidies.…”