Development of onion (Allium cepa L., cv. ÔEarly Cream GoldÕ) seed under cool climate conditions in Tasmania, Australia occurred over a longer duration than previously reported, but similar patterns of change in yield components were recorded. In contrast to previous studies, umbel moisture content declined from 85 to 67 % over 57 days while seed moisture content decreased from 85 to 31 %. Seed yield continued to increase over the duration of crop development, with increasing seed weight compensating for seed loss resulting from capsule dehiscence in the later stages of maturation. Germination percentage was high and did not vary significantly from 53 to 77 days after full bloom (DAF), but mean germination time declined and uniformity of germination increased significantly over the same time period. The percentage abnormal seedlings declined with later harvest date, resulting in highest seed quality at 77 DAF. The results of this study suggest that the decision to harvest cool climate onion seed crops before capsule dehiscence will result in a loss of potential seed yield and quality.
Three types of anomalies in thermal maturity exist within the frontal thrust‐belt of the Ouachita Mountains, Arkansas, USA. The anomalies were documented by combining structural mapping with measurements of vitrinite reflectance; all samples were obtained from surface exposures. Maturity‐inversion occurs along the Y‐City Fault, where Jackfork and Johns Valley strata (Lower Pennsylvanian) have been thrust over less‐mature sequences of the lower Atoka Formation (Middle Pennsylvanian). An apparent shear‐heating aureole is also associated with this important thrust, although the spatial extent of the aureole is limited. When allowances are made for both structural and stratigraphic position, we find that internal gradients in vitrinite reflectance within individual thrust‐sheets are abnormally low. We attribute these gradients to tectonic burial. Weak remnants of the primary stratigraphic gradients are retained in most instances, so organic metamorphic reactions evidently failed to equilibrate during thrust‐loading; rapid unroofing of the thrust‐belt may have begun even as some faults remained active. Similar patterns of maturation should be expected within other thrust‐belts where peak burial and heating events were synchronous with deformation. Under these circumstances, subsurface projections of maturation trends should be keyed to structural (rather than stratigraphic) position.
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