1. Department of Mathematics University of Nebraska‐Lincoln Lincoln Nebraska 68588 USA
2. Department of Agronomy and Horticulture University of Nebraska‐Lincoln Lincoln Nebraska 68588 USA
3. Department of Agronomy University of Wisconsin‐Madison Madison Wisconsin 53706 USA
4. Department of Agriculture, Nutrition and Veterinary Sciences University of Nevada‐Reno Reno Nevada 89557 USA
5. School of Biological Sciences and Department of Mathematics University of Nebraska‐Lincoln Lincoln Nebraska 68588 USA