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No abstract

A ternary model system, sodium stearate (NaSt) crystallites dispersed in mixtures of water and propylene glycol (PG) at 1-5 wt % NaSt concentrations, has been studied. Two different morphologies, fibers and platelets, were observed with light and electron microscopy. At the molecular level, however, these two morphologies share the same layered crystalline structure as revealed by X-ray diffraction. NaSt fibers occur in water-rich mixtures, and by cryogenic electron microscopy they are shown as lamellar ribbons. With increasing PG/H2O ratios in the NaSt/H2O/PG system, platelike crystallites become the preferred morphology. The rheological properties of these suspensions were studied and correlated with the observed morphologies. Decreasing solvent polarity induced morphological transformation from fibers to plates, as further demonstrated by changing solvents from water, to glycerin, to ethylene glycol, and to propylene glycol. The delineation of these trends can be useful in the design of cleaning products. Additionally, in a brief study of sodium myristate (NaMy) in water, we conclude that the NaMy fibers are lamellar crystals.

Crude soybean oil contains phospholipids (2.5 wt%) that must be removed from oil during processing. A common method is the water-degumming process. A ternary phase diagram of soybean oil-water-soybean PC, a major component of phospholipids, was established. From this diagram, phase transitions and compositions of phases can be determined. A theoretical model describing the relationship between aggregation curvature and the amount of water added is presented to explain the phase transitions. The amount of water absorption by the lamellar phase should be larger than the critical value of 34 wt% based on the total weight of water and PC. Below this critical amount, phospholipids tend to form liposomes. Above the critical point and below the saturation point, larger aggregates of particles form and can be easily separated. When more water is added to reach the water adsorption limit, about 40 wt% based on the total weight of water and PC, a phase transition boundary is observed, beyond which a third phase, water, appears and the particle size falls dramatically. In between the critical line predicted by the model and the water adsorption saturation line observed experimentally, there is an operation window on the ternary phase diagram for the water-degumming process.

Wheat stripe rust,

Wheat stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici, is one of the most destructive plant diseases in China. Gansu and Ningxia Provinces are considered to be the key areas for over-summering of this pathogen in China. In this study, 283 P. striiformis f. sp. tritici isolates were collected in these two provinces. Amplified fragment length polymorphism (AFLP) was used to analyze the population genetics and to infer the chance of population exchanges between different geographic locations and seasons. The genotypic diversity of the Gansu population (0.514) was slightly higher than that of the Ningxia population (0.489). The occurrence of frequent population exchanges between these two regions was observed, showing that 40 AFLP genotypes were shared by the populations of the two provinces. Gene flow between these two regions in autumn and spring subpopulations was also detected. The genotype distribution in three populations of Ningxia from opposite sides of the Liupan Mountains revealed possible significant effects of the mountains on limiting gene flow and population exchange. Phylogenetic analysis confirmed the possibility of recombination in some of the studied subpopulations in both provinces.

Puccinia striiformis f. sp. tritici is the causal pathogen of interregional epidemics of wheat stripe rust in China via long-distance migration. Gansu Province serves as putative inoculum center providing oversummering inoculum, while Sichuan Basin area serves as a region providing huge amounts of overwintering inoculum. Thus, the relationship between these two regions in population exchange and migration become important in prediction of interregional epidemics. In this study, we compared the population genetic structure and race composition between Gansu and Sichuan Basin populations to infer their migration relationships. A total of 526 isolates, spanning 3 years, were genotyped using eight pairs of amplified fragment length polymorphism markers, and a subset of 98 isolates were inoculated onto 19 Chinese differentials to perform the race analysis. Twenty-three common races and 26 shared genotypes supplied molecular evidence for migration between Gansu and Sichuan Basin populations. Bayesian assignment and principal component analysis revealed that the genetic group assignment of the Sichuan Basin populations (10SB and 11SB) changed in the spring to align with the fall Gansu populations in the prior seasons (09GS and 10GS), which indicated an asymmetric migration from Gansu Province to the Sichuan Basin area. The linkage disequilibrium and the parsimony tree length permutation test revealed a strong annual recombination signal in the Gansu populations and an inconsistent signal in the Sichuan Basin populations.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most important fungal diseases of wheat in China. Xinjiang, Qinghai, and Gansu Provinces, located in the northwest of China, are the key regions for interregional epidemics of wheat stripe rust due to their geographic as well as crop-planting features, in relation to pathogen’s life cycle, reproduction, and population genetics. To study the population genetic structures of the pathogen in these areas, 217 isolates of P. striiformis f. sp. tritici were collected from different geographic locations at various elevations in the three provinces. The amplified fragment length polymorphism (AFLP) genotypes and virulence phenotypes were analyzed for Xinjiang, Qinghai, and Gansu populations. Frequent genotypic exchanges between Xinjiang and Qinghai and between Qinghai and Gansu populations were detected, demonstrating that the populations of Xinjiang and Gansu may not be completely isolated. Genotypic diversity in Gansu Province was much higher than that in Xinjiang or Qinghai Province. The Xinjiang population was genetically closer to the Qinghai population than to the Gansu population. The race dynamic patterns in Qinghai were consistent with those in Gansu but the similar component pattern of the race dynamics in Xinjiang appeared late, following those in Gansu and other interior epidemic regions of China. No significant correlation between the AFLP genetic distance and the virulence distance in the Xinjiang, Qinghai, and Gansu populations was determined. A possible recombination signature of the pathogen population was detected in Gansu population and some subpopulations in Qinghai but not in Xinjiang population.