No abstract

Leaf collection from the field, labeling and tracking back to the source plants after genotyping are rate limiting steps in leaf DNA-based genotyping. In this study, an optimized genotyping method using endosperm DNA sampled from single maize seeds was developed, which can be used to replace leaf DNA-based genotyping for both genetic studies and breeding applications. A similar approach is likely to be suitable for all plants with relatively large seeds. Part of the endosperm was excised from imbibed maize seeds and DNA extracted in 96-tube plates using individuals from eight F 2 populations and seven inbreds. The quality of the resultant DNA was functionally comparable to DNA extracted from leaf tissue. Extraction from 30 mg of endosperm yields 3-10 lg DNA, which is sufficient for analysis of 200-400 agarose-gel PCR-based markers, with the potential for several million chip-based SNP marker analyses. By comparing endosperm DNA and leaf DNA for individuals from an F 2 population, genotyping errors caused by pericarp contamination and hetero-fertilization were found to average 3.8 and 0.6%, respectively. Endosperm sampling did not affect germination rates under controlled conditions, although under normal field conditions the germination rate, seedling establishment, and growth vigor were significantly lower than that of non-sampled controls for some genotypes. However, careful field management can compensate for these effects. Seed DNA-based genotyping lowered costs by 24.6% compared to leaf DNA-based genotyping due to reduced field plantings and labor costs. A substantial advantage of this approach is that it can be used to select desirable genotypes before planting. As such it provides an opportunity for dramatic improvements in the efficiency and selective gain of breeding systems based on optimum combinations of markerassisted selection and phenotypic selection within and between generations.

To increase genetic gain for tolerance to drought, we aimed to identify environmentally stable QTL in per se and testcross combination under well-watered (WW) and drought stressed (DS) conditions and evaluate the possible deployment of QTL using marker assisted and/or genomic selection (QTL/GS-MAS). A total of 169 doubled haploid lines derived from the cross between CML495 and LPSC7F64 and 190 testcrosses (tester CML494) were evaluated in a total of 11 treatment-by-population combinations under WW and DS conditions. In response to DS, grain yield (GY) and plant height (PHT) were reduced while time to anthesis and the anthesis silking interval (ASI) increased for both lines and hybrids. Forty-eight QTL were detected for a total of nine traits. The allele derived from CML495 generally increased trait values for anthesis, ASI, PHT, the normalized difference vegetative index (NDVI) and the green leaf area duration (GLAD; a composite trait of NDVI, PHT and senescence) while it reduced trait values for leaf rolling and senescence. The LOD scores for all detected QTL ranged from 2.0 to 7.2 explaining 4.4 to 19.4% of the observed phenotypic variance with R2 ranging from 0 (GY, DS, lines) to 37.3% (PHT, WW, lines). Prediction accuracy of the model used for genomic selection was generally higher than phenotypic variance explained by the sum of QTL for individual traits indicative of the polygenic control of traits evaluated here. We therefore propose to use QTL-MAS in forward breeding to enrich the allelic frequency for a few desired traits with strong additive QTL in early selection cycles while GS-MAS could be used in more mature breeding programs to additionally capture alleles with smaller additive effects.

Purpose: To quantitatively describe the structural corneal changes from infancy to early adulthood using ultrasound biomicroscopy. Methods: In this prospective study, 168 ultrasound biomicroscopy images were obtained from 24 healthy eyes of 24 patients who consented and enrolled in the Pediatric Anterior Segment Imaging Innovation Study. Their ages ranged from birth to 26 years. An established ultrasound biomicroscopy imaging protocol including seven views of one eye per patient were obtained and measured using ImageJ software (National Institutes of Health). Twelve corneal structural parameters were measured. Means were compared between younger and older groups. Results: Among the 12 measured structures, 5 demonstrated statistically significant differences ( P < .05) between patients younger than 1 year and patients older than 1 year. The mean values for corneal cross-sectional width and length, central corneal thickness, and radii of curvature (anterior and posterior) were significantly different in patients younger than 1 year. Curvature and limbus-to-limbus dimensions changed more dramatically than thickness and tissue density. When comparing the youngest to oldest subgroups, anterior curvature flattened (6.14 to 7.55 radius), posterior curvature flattened (5.53 to 6.72 radius), angle-to-angle distance increased (8.93 to 11.40 mm), and endothelial cross-sectional distance increased (10.63 to 13.61 mm). Conclusions: Pediatric corneal structures change with age. The most significant changes occur in the first months of life, with additional changes later in childhood. This study further demonstrates the importance of age in pediatric corneal imaging analysis. [ J Pediatr Ophthalmol Strabismus. 2020;57(4):238–245.]