Frequency of Polyploids of Solanum tuberosum Dihaploids in 2X × 2X Crosses

When breeding diploid potatoes, tetraploid progeny can result from the union of 2n eggs and 2n pollen in 2x-2x crosses. Thirty-three crosses were made to examine tetraploid progeny frequency in 2x-2x crosses. All crosses were between S. tuberosum dihaploids and diploid self-compatible donors, M6 and DRH S6-10-4P17. Using chloroplast counting for ploidy determination, the frequency of tetraploid progeny was as high as 45% in one of the 33 crosses. Based upon single nucleotide polymorphism (SNP) genotyping, the tetraploid progeny were attributed to bilateral sexual polyploidization (BSP), which is caused by the union of 2n egg and 2n pollen. Dihaploids were identified that produce lower frequencies of 2n eggs. The results of this study suggest that S. tuberosum dihaploids with a high frequency of 2n eggs should be avoided in 2x - 2x crosses for diploid breeding programs.

Erratic Male Meiosis Resulting in2nPollen Grain Formation in a 4x Cytotype (2n=28) ofRanunculus laetusWall. ex Royle

Two accessions were studied for male meiosis inRanunculus laetusfrom the cold regions of Northwest Himalayas. One accession showed the presence of 14 bivalents at diakinesis and regular segregation of bivalents at anaphase I which lead to normal tetrad formation with fournmicrospores and consequentlynpollen grains and 100% pollen fertility. Second accession from the same locality revealed the erratic meiosis characterized by the presence of all the 28 chromosomes as univalents in meiocytes at metaphase I. Univalent chromosomes failed to segregate during anaphases and produced restitution nuclei at meiosis I and II. These restitution nuclei resulted into dyads and triads which subsequently produced two types of apparently fertile pollen grains. On the basis of size, the two types of pollen grains were categorized asn(normal reduced) and2n(unreduced, 1.5-times larger than thenpollen grains). The estimated frequency of2npollen grains from dyads and triads (61.59%) was almost the same as that of the observed one (59.90%), which indicated that2npollen grains inR. laetuswere the result of dyads and triads. The present paper herein may provide an insight into the mechanisms of the formation of various intraspecific polyploids through sexual polyploidization inR. laetus.