Molecular characterization of a given set of maize germplasm could be useful for understanding the use of the assembled germplasm for further improvement in a breeding program, such as analyzing genetic diversity, selecting a parental line, assigning heterotic groups, creating a core set of germplasm and/or performing association analysis for traits of interest. In this study, we used single nucleotide polymorphism (SNP) markers to assess the genetic variability in a set of doubled haploid (DH) lines derived from the unselected Iowa Stiff Stalk Synthetic (BSSS) maize population, denoted as C0 (BSSS(R)C0), the seventeenth cycle of reciprocal recurrent selection in BSSS (BSSS(R)C17), denoted as C17 and the cross between BSSS(R)C0 and BSSS(R)C17 denoted as C0/C17. With the aim to explore if we have potentially lost diversity from C0 to C17 derived DH lines and observe whether useful genetic variation in C0 was left behind during the selection process since C0 could be a reservoir of genetic diversity that could be untapped using DH technology. Additionally, we quantify the contribution of the BSSS progenitors in each set of DH lines. The molecular characterization analysis confirmed the apparent separation and the loss of genetic variability from C0 to C17 through the recurrent selection process. Which was observed by the degree of differentiation between the C0_DHL versus C17_DHL groups by Wright’s F-statistics (FST). Similarly for the population structure based on principal component analysis (PCA) revealed a clear separation among groups of DH lines. Some of the progenitors had a higher genetic contribution in C0 compared with C0/C17 and C17 derived DH lines. Although genetic drift can explain most of the genetic structure genome-wide, phenotypic data provide evidence that selection has altered favorable allele frequencies in the BSSS maize population through the reciprocal recurrent selection program.
Coffee seeds rapidly lose viability during storage, which hinders the development of vigorous seedlings for crop establishment. There are reports that seed endosperm is more sensitive to deterioration than embryos, which can be excised and cultivated in vitro. However, a substantial number of plants grown in vitro do not survive during transfer to a greenhouse or field environment. The objective of this study was to evaluate the acclimatization of coffee seedlings of cultivar Catuaí Amarelo IAC 62, developed from zygotic embryos obtained from aged seeds in different substrates and environments, for the production of well-developed seedlings suitable for planting. For this purpose, seedlings were obtained from the in vitro cultivation of embryos obtained from seeds of two quality levels: freshly harvested seeds and artificially aged seeds. Zygotic embryos were extracted from the seeds and cultivated in MS medium. At 60 days, the percentages of normal and abnormal seedlings and dead seeds were evaluated. The good-quality seedlings grown in vitro for 60 days were transplanted into two different substrates (Tropstrato and coconut fiber) and acclimatized in two environments (growth room and greenhouse with a misting system). The plants were evaluated for height, stem diameter, number of leaves, chlorophyll content, and growth rate. The greenhouse environment was better for seedling growth, possibly due to its higher sunlight and temperature. The best substrate was coconut fiber, as it ensured better development of plants from freshly harvested seeds and those from aged seeds. It is possible to develop healthy seedlings from seeds with low viability
During drying and freezing, protective mechanisms act to maintain seed physiological quality. Some of these mechanisms contribute to the integrity of cell membranes. The damage caused to cell membranes due to cell stress can be seen in ultrastructural studies, comparing these results to those of physiological evaluation. The aim of this study was to investigate ultrastructural changes in endosperm cells of coffee seeds brought about by drying and by exposure to low temperatures. Seeds of Coffea arabica were dried in silica gel to moisture contents of 40, 20, and 5 % (wb) and brought to equilibrium at temperatures of 10,-20, and-86 o C. Germination, vigor, and tetrazolium tests were performed for evaluation of seed physiological quality. Ultrastructural damage was analyzed by scanning electron microscopy. Coffee seeds with 40% moisture content have whole, swollen, and expanded cells, with a filled lumen and without signs of damage. The physiological and ultrastructural quality of seeds exposed to below zero temperatures with 40% moisture content is compromised. They have null germination and empty cells, indicating leakage of cell content. Drying of coffee seeds leads to uniform contraction of inner cell content. Drying of coffee seeds to 5% moisture content leads to intense contraction of cell volume, with physiological and ultrastructural damage.
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