Maternal effects and germination timing mediate the expression of winter and spring annual life histories in Arabidopsis thaliana

In natural populations of the annual plant Arabidopsis thaliana, season of germination determines life history. Spring annuals overwinter as seeds and germinate and flower in spring. Winter annuals germinate in fall, overwinter as rosettes, and flower in spring. In many plant species, germination is affected by the maternal phenotype during seed production. In those that produce seeds on branches from the main stem and branches from basal nodes, like A. thaliana, there may be positional effects on germination. This study examines the effects of maternal branch type on germination in artificial seasonal spring and fall environments. Seeds from apical and basal branches of 41 accessions of A. thaliana were weighed and divided between spring (low temperature for 21 d) and fall (ambient temperature) germination environments. Maternal branch type had significant effects on germination fraction and seed mass, but the direction of the effect differed among accessions. The genetic correlation between seed mass and germination fraction was positive for seeds in the spring germination environment and negative in the fall germination environment. There was a positive longitudinal cline for seed mass, a negative longitudinal cline for germination fraction, and a latitudinal cline for germination fraction that depended on the germination environment. These results show that there is geographic variation in germination traits and suggest that genetic variation in mass can lead to variation in season of germination for A. thaliana.