ARS physiologist John Burke and postdoctoral researcher Rao Kottapalli perform a chlorophyll fluorescence assay on peanut leaf samples from irrigated and drought-stressed plants. This assay is one of several that are used to screen germplasm for variability in abiotic stress tolerance. The monitor in the background shows an image of a peanut DNA microarray that is used to identify genes involved in stress response and to compare contrasting germplasm.