A rapid means of sex identification in Silene latifolia by use of flow cytometry

Sex identification in dioecious plants using nonflowering material would have broad applications in both basic and applied research. We present a method using flow cytometry for diagnosing the sex of the dioecious species Silene latifolia Poiret (Caryophyllaceae) by means of sexual differences in nuclear DNA content and base-pair composition. Males have a significantly larger genome, attributable to the known sex-chromosome heteromorphism. Males and females also differ in the AT/GC composition, attributable to differences in non-recombining portions of the sex chromosomes. The two measures enable assignment of individuals to sex with a combined error rate of 9%. These results for S. latifolia indicate useful directions for future research into sex diagnostics for other dioecious species.</p

A rapid means of sex identification in Silene latifolia by use of flow cytometry

Sex identification in dioecious plants using nonflowering material would have broad applications in both basic and applied research. We present a method using flow cytometry for diagnosing the sex of the dioecious species Silene latifolia Poiret (Caryophyllaceae) by means of sexual differences in nuclear DNA content and base-pair composition. Males have a significantly larger genome, attributable to the known sex-chromosome heteromorphism. Males and females also differ in the AT/GC composition, attributable to differences in non-recombining portions of the sex chromosomes. The two measures enable assignment of individuals to sex with a combined error rate of 9%. These results for S. latifolia indicate useful directions for future research into sex diagnostics for other dioecious species.</p

Genome size variation in guayule and mariola: fundamental descriptors for polyploid plant taxa

Citation: Sanchez, P., . . . & Gore, M. (2013). Genome size variation in guayule and mariola: Fundamental descriptors for polyploid plant taxa. Industrial Crops and Products, 54(1), 1-5. https://doi.org/10.1016/j.indcrop.2013.12.052Guayule (Parthenium argentatum A. Gray) has tremendous potential as a domestic source of natural rubber production in the southwestern United States. However, genetic improvement of guayule has been slowed by its complex mode of reproduction, natural ploidy series, and lack of genetic and genomic resources. The interspecific hybridization of guayule with its closest sister taxon mariola (P. incanum Kunth) offers an opportunity to access novel genetic variation for guayule breeding programs, but mariola accessions available from the U.S. National Plant Germplasm System (NPGS) have never been evaluated for natural variation in ploidy level. In addition, the nuclear genome sizes for guayule and mariola at any ploidy level are unknown. To that end, we examined the ploidy of 10 mariola accessions, which revealed a natural polyploid series ranging from triploid (2n = 3x = 54) to pentaploid (2n = 5x = 90). In contrast, a ploidy analysis of five guayule accessions uncovered a natural polyploid series that ranged from diploid (2n = 2x = 36) to hexaploid (2n = 6x = 108). More than one ploidy level among individual plants (mixed ploidy) and instances of aneuploid plants were observed for accessions of both guayule and mariola. The nuclear genome sizes of guayule and mariola were similar at identical ploidy levels, and the genome size of diploid guayule (1624 Mb) was almost twofold smaller than the genomes of sunflower (H. annuus L. 2n = 2x = 34) and lettuce (L. sativa L.; 2n = 2x = 18), two other Compositae (Asteraceae) species that are being genome-sequenced. The results from this study will serve as a foundation for interspecific breeding and genome sequencing of guayule and mariola

Association Mapping: Critical Considerations Shift from Genotyping to Experimental Design

The goal of many plant scientists' research is to explain natural phenotypic variation in terms of simple changes in DNA sequence. Traditionally, linkage mapping has been the most commonly employed method to reach this goal: experimental crosses are made to generate a family with known relatedness, and attempts are made to identify cosegregation of genetic markers and phenotypes within this family. In vertebrate systems, association mapping (also known as linkage disequilibrium mapping) is increasingly being adopted as the mapping method of choice. Association mapping involves searching for genotype-phenotype correlations in unrelated individuals and often is more rapid and cost-effective than traditional linkage mapping. We emphasize here that linkage and association mapping are complementary approaches and are more similar than is often assumed. Unlike in vertebrates, where controlled crosses can be expensive or impossible (e.g., in humans), the plant scientific community can exploit the advantages of both controlled crosses and association mapping to increase statistical power and mapping resolution. While the time and money required for the collection of genotype data were critical considerations in the past, the increasing availability of inexpensive DNA sequencing and genotyping methods should prompt researchers to shift their attention to experimental design. This review provides thoughts on finding the optimal experimental mix of association mapping using unrelated individuals and controlled crosses to identify the genes underlying phenotypic variation

The abandonment of maize landraces over the last 50 years in Morelos, Mexico: a tracing study using a multi-level perspective

Understanding the causes of maize landrace loss in farmers’ field is essential to design effective conservation strategies. These strategies are necessary to ensure that genetic resources are available in the future. Previous studies have shown that this loss is caused by multiple factors. In this longitudinal study, we used a collection of 93 maize landrace accessions from Morelos, Mexico, and stored at the International Maize and Wheat Improvement Center (CIMMYT) Maize Germplasm Bank, to trace back to the original 66 donor families after 50 years and explore the causes for why they abandoned or conserved their seed lots. We used an actor-centered approach, based on interviews and focus group discussions. We adopt a Multi-Level Perspective framework to examine loss as a process, accommodating multiple causes and the interactions among them. We found that the importance of maize landrace cultivation had diminished over the last 50 years in the study area. By 2017, 13 families had conserved a total of 14 seed lots directly descended from the 1967 collection. Focus group participants identified 60 accessions that could still be found in the surrounding municipalities. Our findings showed that multiple interconnected changes in maize cultivation technologies, as well as in maize markets, other crop markets, agricultural and land policies, cultural preferences, urbanization and climate change, have created an unfavorable environment for the conservation of maize landraces. Many of these processes were location- and landrace-specific, and often led to landrace abandonment during the shift from one farmer generation to the next.</p