Genetic diversity and selection signatures in maize landraces compared across 50 years of in situ and ex situ conservation

Genomics-based, longitudinal comparisons between ex situ and in situ agrobiodiversity conservation strategies can contribute to a better understanding of their underlying effects. However, landrace designations, ambiguous common names, and gaps in sampling information complicate the identification of matching ex situ and in situ seed lots. Here we report a 50- year longitudinal comparison of the genetic diversity of a set of 13 accessions from the state of Morelos, Mexico, conserved ex situ since 1967 and retrieved in situ from the same donor families in 2017. We interviewed farmer families who donated in situ landraces to understand their germplasm selection criteria. Samples were genotyped by sequencing, producing 74,739 SNPs. Comparing the two sample groups, we show that ex situ and in situ genome-wide diversity was similar. In situ samples had 3.1% fewer SNPs and lower pairwise genetic distances (Fst 0.008–0.113) than ex situ samples (Fst 0.031–0.128), but displayed the same heterozygosity. Despite genome-wide similarities across samples, we could identify several loci under selection when comparing in situ and ex situ seed lots, suggesting ongoing evolution in farmer fields. Eight loci in chromosomes 3, 5, 6, and 10 showed evidence of selection in situ that could be related with farmers’ selection criteria surveyed with focus groups and interviews at the sampling site in 2017, including wider kernels and larger ear size. Our results have implications for ex situ collection resampling strategies and the in situ conservation of threatened landraces

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

Diversity and conservation priorities of crop wild relatives in Mexico

Crop wild relatives (CWR) are valuable resources for crop breeding due to their close genetic relationship to the cultivated plants and their wide genetic variation, allowing the introgression of desirable traits into the crops, such as resistance to plant pests and diseases or adaptability to climate change. Mexico is a centre of agrobiodiversity, including CWR, but climate change, and other factors, are contributing to the loss of important Mexican CWR genetic diversity. The in situ and ex situ conservation status of Mexican priority CWR were assessed through a gap analysis as part of a national CWR conservation strategy for Mexico, to ensure the long-term preservation and improve the availability of these genetic resources. A set of 310 priority CWR taxa, previously identified as part of the national CWR inventory for Mexico, were analysed. Species distribution modelling and ecogeographic diversity analyses were used to detect gaps in in situ and ex situ conservation at taxon and ecogeographic levels. Priority target sites were identified throughout the country for complementary in situ and ex situ conservation of these taxa. The results obtained allow us to make recommendations for immediate conservation actions, thus helping to mitigate the threats to Mexican agrobiodiversity and enhance both national and global food security