Variability structure and heritability of germination timing in Capsella bursa‐pastoris (L.) Medik. (Shepherd's purse)

Abstract

Germination variability enables weedy species to colonise disturbed habitats and is expected to evolve in response to changing selection pressures. The paucity of information about germination variability in weeds prompted a detailed study of this topic with two agricultural and two non‐agricultural populations of Capsella bursa‐pastoris (Shepherd's purse). Variance in germination time was partitioned amongst and within populations, and amongst racemes and silicles within individual plant, and broad‐sense heritability (H2) was estimated. Agricultural populations exhibited a shorter and more uniform germination timing than non‐agricultural populations. However, differences amongst populations explained 7%–12% of the total variance, while differences amongst individuals and racemes accounted for approximately 40–54% and 10% of the total variance for germination time. For germination time, H2 = 0.4 when averaged across all time points, peaking at H2 = 0.7 at a time coinciding with the exponential phase of the germination curve. Maintaining predominantly intrapopulation variability in germination timing appears to be important for long‐term fitness in this species.