No description available.

No description available.

No description available.

The serpentine endemic, Mimulus nudatus, lives sympatrically on the serpentine soils of Lake County, California, with its probable progenitor, the bodenvag species M. guttatus. This thesis examined the mechanisms which enable M nudatus and M guttatus to coexist in sympatry. In addition, it sought to determine the genetic basis of the postzygotic reproductive isolating barrier between M nudatus and M guttatus, in order to distinguish between the classical allopatric and the ecotypic models of speciation. The postzygotic barrier achieving reproductive isolation between the species was at the seed provisioning stage and was strong for both local and distant populations of M guttatus. In addition, there was some evidence for premating pollinator isolation, since honey bees preferentially visited M guttatus and Dialictus preferred M. nudatus. In spite of the majority of pollinator visits being intra-specific, M nudatus still suffered a reduction in fertility caused by interspecific crossing, although M guttatus experienced no such reduction. To avoid M nudatus being outcompeted into extinction, the two species must thus be sufficiently ecologically different. In the field and in the greenhouse, whilst M guttatus experienced a reduction in fitness as calcium levels decreased, the fitness of M nudatus was independent of calcium levels. Therefore one hypothesis suggested for the ecological differentiation of the two species, was that M nudatus had evolved greater tolerance to calcium deficient soils. The genetic basis of the postzygotic reproductive isolating barrier between M nudatus and M guttatus was investigated by using crosses to a third species, M cupriphilus, which was used since it gave fertile hybrids with both species. It was not possible to determine the genetic basis of the postzygotic reproductive isolating barrier between M nudatus and M guttatus since the results in the crossing program were contradictory. Some results supported the simple two gene complementary interaction system previously found for populations of M guttatus, but others did not. Hence no distinction could be made between the allopatric and ecotypic models of speciation.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 87-96). Also available in print.

No description available.

To determine the optimal seeding rate and utilization of seed treatment combinations for maximizing soybean yield within optimal and late planting dates. Also, experiments were conducted to quantify effects of soybean stand loss and to determine optimal seeding rates at various planting dates comparing three seed treatments. Experiments were conducted to test influence of planter type and seeding rate on soybean. Soybean seed treated with at planting insecticides showed no difference in yield compared to fungicide only treated seed. Also, yields were maximized at low seeding rates where no stand loss occurred. Soybean yields benefited from where seeding rates were increased at 20% and 40% stand loss. Higher seeding rates can provide significant risk of yield and economic losses if no stand loss occurs. Optimal plantings can significantly increase soybean yields compared to later plantings. There was a significant difference in yield where fungicide only treated seed was planted compared to seed treated with a neonicotinoid. Low seeding rates maximized yield at optimal planting dates but were penalized at late planting dates. Soybean yields benefited from increased seeding rates at the later planting dates but there was no difference in any of the seed treatments compared to untreated soybean. Also, there was less variation in inter-spacing of plants at the lower seeding rate compared to higher seeding rate when using the cone planter compared to the other planter types. There was no difference in yield for soybean planted with any of the evaluated planter types. Yield differences were observed from higher seeding rate compared to low seeding rate.

published_or_final_version / Biological Sciences / Master / Master of Philosophy

Thesis (Ph. D.)--Oregon State University, 1993. / Typescript (photocopy). Includes bibliographical references (leaves 91-95). Also available on the World Wide Web.

Dissertation (PhD)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.