Recessive male floret color for tracking gene flow in cultivated northern wild rice (Zizania palustris L.)

Northern wild rice (NWR; Zizania palustris L.) is a wind-pollinated, annual, aquatic grass that grows naturally in the Great Lakes region of the United States and Canada and is also cultivated in flooded paddies, predominantly in California and Minnesota. A better understanding of pollen-mediated gene flow is needed within the species for both conservation and breeding efforts as cultivation occurs within the species’ natural range and spatially-isolated, paddy structures are limited within breeding programs. Widely-cited pollen travel research in NWR demonstrated that pollen could travel at least 3200 m. However, a population segregating for male sterility was used as the pollen recipient in the study and was determined to not be adequate for NWR pollen travel studies. Here, we present the characterization of a recessive white male floret (WMF) population in contrast to the dominant, purple male floret (PMF) color of cultivated NWR along with estimates of pollen-mediated gene flow in a cultivated paddy setting. Studies conducted in 2018 and 2019 revealed that the primary amount of pollen-mediated gene flow occurred within the first 7 m from the PMF donor source with no gene flow detected past 63 m. These results suggest that the likelihood of pollen-mediated gene flow between cultivated NWR and natural stands remains low. We also identified a strong linkage between male floret, collar, and culm color. This study demonstrates that the WMF trait is an excellent candidate for use in pollen-mediated gene flow studies in NWR.