Can Population Crosses Be a Means to Exploit Heterosis in American Wildrice?.

American wildrice (Zizania palustris L.) is a cross-pollinating crop with a recent domestication history in North America. When self-pollinated, it undergoes severe inbreeding depression. Seed storage problems also continue to hamper the development of inbred lines that could be used as the basis for a hybrid breeding program. One alternative is to identify advanced breeding populations of distinct origins that may be genetically divergent enough to display heterosis when a large number of non-inbred individuals from the populations are intermated to form a population cross. Five such populations were intermated with each other in a non-reciprocal diallel fashion by planting and emasculating "female" population rows within "male" population blocks. The resulting F₁ seeds were tested for heterosis in a single-location yield trial against their parent populations the first year. Yield, seed shattering, seed size, panicle length, and other traits were measured. Little evidence of heterotic combinations was found in this trial. Several of the F₁ population crosses were grown out in blocks and carried forward to the F₂ generation. Seeds of the F₂ generation as well as remnant F₁ seeds were planted in a second trial and re-tested against their parent populations the following year. Additional population crosses were also tested in a separate trial. Second year results are pending. Diversity analysis of parent populations using highly polymorphic SSR markers will provide an estimate of the genetic distances between the populations.