SSR Markers Reveal Extremely High Outcrossing Fertility of Lowland Switchgrass Under Naturally Open Pollinating Conditions

Switchgrass (Panicum virgatum L.) is being developed as a major cellulosic crop for bioenergy production.  However, no information is available on mating behavior of plants under naturally open pollinating conditions. Accordingly, the objective of this study was to quantify selfing and outcrossing rates of switchgrass plants grown in the field. Two small (NL94 C2-3 and SL93 C2-3), each having 5 parents and two large (NL94 C3 and SL93 C3), each having 26 parents, lowland switchgrass breeding populations field established with three replications were used in the experiment for two years.   Ten seedlings from open-pollinated seeds of each parent per replication were developed in a greenhouse at the Agronomy Research Station, Oklahoma State University, resulting in 30 progeny plants (10 plants by three replications) per parent each year. In 2010, DNA samples were isolated from 1700 progeny of 62 seed parents while DNA samples were extracted from 773 progeny of the same parents in 2011. Sixteen Simple Sequence Repeat (SSR) markers were used to identify breeding origins of the progeny plants as compared with respective seed parents. Among 2473 progeny examined over the two years, only one progeny of SL93 4x4 was identified to be selfed, indicating an extremely high outcrossing rate of 99.96%.  And it appears there were no significant effects on outcrossing mating behavior in lowland switchgrass due to genotypes and environmental factors.  The findings should help better understand the sexual reproduction characteristics of lowland switchgrass and the identified selfed progeny could be useful in inbred line development.