Studies on rice transformation and the use of transformed plants [electronic resource]

This research was conducted to enhance utilization of the Liberty herbicide resistance transgene in rice. Non-lethal methods to determine the sensitivity of transgenic rice plants to hygromycin B and Liberty were developed, tested and used in this research. Four homozygous transformed plants were selected to make reciprocal crosses with their non-transformed parent cultivars Taipei 309 and Nipponbare. Their resistances to Liberty and hygromycin B were controlled by the closely linked single dominant genes bar and hpt. Some non-resistant phenotypes in the F2 populations were due to gene silencing. The bar gene in some of these plants were allelic and some were non-allelic. When seven independently transformed homozygous transgenic plants with bar and hygromycin genes from Taipei 309 and Nipponbare were crossed reciprocally, progeny evaluations showed five allelic locations among the seven transgenic plants. Twenty additional homozygous transgenic plants from independent transformation events were crossed reciprocally with the previous seven transgenic plants. Evaluation of F1, F2, and F3 populations showed that some of the genes were allelic, but most of them were non-allelic with two or more pairs of genes being expressed. The functional foreign gene (bar) appeared to be restrictively inserted into the rice genome in some cases and was not randomly inserted and expressed. Three to five repeated backcrosses were made using transgenic plants as the donor and current cultivars as the recurrent parents. The results from selected progeny rows, and two-years of yield tests with selected lines, indicated that the target bar gene could be transferred to lines similar to commercial cultivars from homozygous transformants in 4-5 years of backcrossing, giving lines similar to the recurrent parents based on phenotype and yield potential. Liberty herbicide has antibiotic characteristics and suppressed growth of several rice fungal pathogens and Burkholderia glumae in in vitro tests. Liberty had a short residual activity against Rhizoctonia solani in field tests, but single applications of Liberty after disease development had started in the field significantly reduced sheath blight ratings and yield loss. Control of sheath blight by Liberty was equal to or better than that given by the registered fungicide Quadris

Highly efficient spin-orbit torque and switching of layered ferromagnet Fe3GeTe2

Among van der Waals (vdW) layered ferromagnets, Fe3GeTe2 (FGT) is an excellent candidate material to form FGT/heavy metal heterostructures for studying the effect of spin-orbit torques (SOT). Its metallicity, strong perpendicular magnetic anisotropy built in the single atomic layers, relatively high Curie temperature (Tc about 225 K) and electrostatic gate tunability offer a tantalizing possibility of achieving the ultimate high SOT limit in monolayer all-vdW nanodevices. The spin current generated in Pt exerts a damping-like SOT on FGT magnetization. At about 2.5x1011 A/m2 current density,SOT causes the FGT magnetization to switch, which is detected by the anomalous Hall effect of FGT. To quantify the SOT effect, we measure the second harmonic Hall responses as the applied magnetic field rotates the FGT magnetization in the plane. Our analysis shows that the SOT efficiency is comparable with that of the best heterostructures containing three-dimensional (3D) ferromagnetic metals and much larger than that of heterostructures containing 3D ferrimagnetic insulators. Such large efficiency is attributed to the atomically flat FGT/Pt interface, which demonstrates the great potential of exploiting vdW heterostructures for highly efficient spintronic nanodevices