BackgroundGenotyping-by-sequencing (GBS) has been used broadly in genetic studies for several species, especially those with agricultural importance. However, its use is still limited in autopolyploid species because genotype calling software generally fails to properly distinguish heterozygous classes based on allele dosage.ResultsVCF2SM is a Python script that integrates sequencing depth information of polymorphisms in variant call format (VCF) files and SuperMASSA software for quantitative genotype calling. VCFs can be obtained from any variant discovery software that outputs exact allele sequencing depth, such as a modified version of the Tassel-GBS pipeline provided here. VCF2SM was successfully applied in analyzing GBS data from diverse panels (alfalfa and potato) and full-sib mapping populations (alfalfa and switchgrass) of polyploid species.ConclusionsWe demonstrate that our approach can help plant geneticists working with autopolyploid species to advance their studies by distinguishing allele dosage from GBS data.Electronic supplementary materialThe online version of this article (10.1186/s12859-018-2433-6) contains supplementary material, which is available to authorized users.

One of the current challenges of tropical fruit crop improvement is to incorporate molecular marker-based approaches into conventional breeding programmes. This study was designed to build an integrated genetic map of the sweet passion fruit (Passiflora alata), a diploid (2n = 18) outcrossing species which is greatly appreciated for in natura consumption, and reported to inspire cosmetic and pharmaceutical companies to create plant-derived compounds. With this in mind, a full-sib family of 180 individuals was genotyped using different molecular marker types, such as amplified fragment length polymorphisms (AFLP), microsatellite-AFLP (M-AFLP), simple sequence repeats (SSR), resistance gene analogues (RGA) and target region amplification polymorphism (TRAP). On average, the rate of polymorphism between the parental genotypes was 20.3%. We also searched for single nucleotide polymorphisms (SNPs) in some AFLP bands and in seven gene fragments, and found one SNP every 87 bp. All SNPs were biallelic and occurred most frequently in putative gene fragments (81.5%) rather than in AFLP bands (60.0%) analyzed. Excellent gel profiles were obtained allowing the recognition of all types of segregation expected for a progeny of an outcrossing species. Multipoint linkage analysis was performed using OneMap software, with logarithm of the odds (LOD) score ≥ 5.6 and recombination fraction <0.5. The resulting integrated map consists of 549 markers, 2.0% of which fit a segregation ratio of 1:1:1:1, 1.3% a ratio of 1:2:1, 27.3% a ratio of 3:1 and 69.4% a ratio of 1:1. The map spanned a total of 2073.0 cM, with an average distance between adjacent markers of 3.8 cM. This is the first linkage study on sweet passion fruit and should prove useful for quantitative trait loci mapping.

Plant cytogenetic studies have provided essential knowledge on chromosome behavior during meiosis, contributing to our understanding of this complex process. In this review, we describe in detail the meiotic process in auto- and allopolyploids from the onset of prophase I through pairing, recombination, and bivalent formation, highlighting recent findings on the genetic control and mode of action of specific proteins that lead to diploid-like meiosis behavior in polyploid species. During the meiosis of newly formed polyploids, related chromosomes (homologous in autopolyploids; homologous and homoeologous in allopolyploids) can combine in complex structures called multivalents. These structures occur when multiple chromosomes simultaneously pair, synapse, and recombine. We discuss the effectiveness of crossover frequency in preventing multivalent formation and favoring regular meiosis. Homoeologous recombination in particular can generate new gene (locus) combinations and phenotypes, but it may destabilize the karyotype and lead to aberrant meiotic behavior, reducing fertility. In crop species, understanding the factors that control pairing and recombination has the potential to provide plant breeders with resources to make fuller use of available chromosome variations in number and structure. We focused on wheat and oilseed rape, since there is an abundance of elucidating studies on this subject, including the molecular characterization of the Ph1 (wheat) and PrBn (oilseed rape) loci, which are known to play a crucial role in regulating meiosis. Finally, we exploited the consequences of chromosome pairing and recombination for genetic map construction in polyploids, highlighting two case studies of complex genomes: (i) modern sugarcane, which has a man-made genome harboring two subgenomes with some recombinant chromosomes; and (ii) hexaploid sweet potato, a naturally occurring polyploid. The recent inclusion of allelic dosage information has improved linkage estimation in polyploids, allowing multilocus genetic maps to be constructed.

The genus Gossypium is composed of both diploid and allotetraploid species. The five allotetraploid species of Gossypium are sexually compatible, and only partial sexual barriers have been described. Natural hybrids among them do not occur or occur in situ with very low frequency in Brazil in the rare places where cultivated upland cotton ( Gossypium hirsutum L.) occurs in a sympatric range with Gossypium barbadense L. or Gossypium mustelinum Miers. We evaluated the presence of pollen competition as a prezygotic barrier in crosses between upland cotton and G. barbadense and G. mustelinum. We found that G. barbadense pollinated with a mixture of 50% upland cotton and 50% G. barbadense pollen resulted in 17.4%–31.1% interspecific hybrids, depending upon the upland cotton genotype used as pollen donor. Mixtures containing pollen from G. mustelinum and upland cotton, used to pollinate G. mustelinum in proportions of 25%:75%, 50%:50%, and 75%:25%, produced 61.3%, 22.5%, and 3.6% interspecific hybrids, respectively. These low rates of hybrid production demonstrate that pollen competition is present with G. mustelinum and G. barbadense and confirms this mechanism as a sexual barrier.

No abstract

No abstract

Breeding for yield and fruit quality traits in passion fruits is complex due to the polygenic nature of these traits and the existence of genetic correlations among them. Therefore, studies focused on crop management practices and breeding using modern quantitative genetic approaches are still needed, especially for Passiflora alata, an understudied crop, popularly known as the sweet passion fruit. It is highly appreciated for its typical aroma and flavor characteristics. In this study, we aimed to reevaluate 30 genotypes previously selected for fruit quality from a 100 full-sib sweet passion fruit progeny in three environments, with a view to estimating the heritability and genetic correlations, and investigating the GEI and response to selection for nine fruit traits (weight, diameter and length of the fruit; thickness and weight of skin; weight and yield of fruit pulp; soluble solids, and yield). Pairwise genetic correlations among the fruit traits showed mostly intermediate to high values, especially those associated with fruit size and shape. Different genotype rankings were obtained regarding the predicted genetic values of weight of skin, thickness of skin and weight of pulp in each environment. Finally, we used a multiplicative selection index to select simultaneously for weight of pulp and against fruit skin thickness and weight. The response to selection was positive for all traits except soluble solids, and the 20% superior (six) genotypes were ranked. Based on the assumption that incompatibility mechanisms exist in P. alata, the selected genotypes were intercrossed in a complete diallel mating scheme. It is worth noting that all genotypes produced fruits, which is essential to guarantee yields in commercial orchards.

No abstract