Improving Navajo spinach (Cleome serrulata Pursh) seed germination with cold stratification and hormone additions

Abstract

Seed germination of Cleome serrulata Pursh (Capparaceae), often called Navajo spinach, stinkweed, or Rocky Mountain beeplant, is often quite low, and ways to increase germination percentage have not been determined. Cleome serrulata produces large amounts of pollen for many insect pollinators, contributes to erosion control, and is occasionally used as forage. The distribution of C. serrulata across the US and Canada suggests chilling and scarification could positively impact seed germination. This study applied various combinations of chilling duration (4 or 8 wk) over a range of temperatures (4 °C [39 °F], 7 °C [45 °F), 10 °C [50 °F], or 20 °C [68 °F; control]), scarification with H₂O₂, and various hormones (GA₃ or GA_4/7 and BA) to C. serrulata seed grown in Logan, Utah (seed source origin was Chinle, Arizona). Initial viability for C. serrulata seed was 94% via tetrazolium testing. Seed germination was responsive to both temperature and hormone applications. As chilling temperature increased from 4 ° to 20 °C (39–68 °F), germination percentage decreased from 50% to less than 2%. Various hormone treatments consisting of GA_4/7 and BA applied prior to chilling resulted in seed germination of greater than 80% whereas less than 10% of untreated seeds germinated. Additionally, the speed of germination (T₅₀) increased with temperature while germination spread (T_10–90) decreased in hormone treatments. Our findings show that chilling duration, gibberellins, and seed after-ripening all influence seed germination and should be used to improve plant establishment.