Cold stratification requirement to break morphophysiological dormancy of fennel (Foeniculum vulgare Mill.) seeds varies with seed length

Abstract

Seed germination plays a significant role in establishment and growth of seedlings. Two factorial experiments were conducted to investigate seed dormancy and germination in fennel (Foeniculum vulgare Mill.) seeds. The first experiment evaluated cold stratification (0, 2, 4, 6, and 8 weeks), gibberellic acid (0, 500, and 2000 ppm), genotypes ('Chahestan' and 'Fasa'), and incubation temperatures (10, 20, and 30 °C). The second experiment examined the effects of cold stratification (0, 2, 4, 6, and 8 weeks), genotypes ('Chahestan' and 'Fasa'), and seed length (large (>4.7 mm), medium (3– 4.7 mm), and small (2–3 mm)). The results from the first experiment showed that the fennel seeds have linear underdeveloped embryos with an embryo length to seed length ratio (E/S ratio) of 0.24–0.28. Four weeks after cold stratification, embryos typically reached to ∼2.5 mm length with an E/S ratio of ∼0.6, and germination percentages of 70%, and 85% in 'Chahestan' and 'Fasa' (treated with 2000 ppm GA3 and incubated at 10 °C). GA3 improved the germination percentage and germination rate, but could not substitute for cold stratification. Thus, seeds of fennel have non-deep simple of morphophysiological dormancy (MPD). In the second experiment, we found that across all stratification periods, large seeds had longer embryos than medium and small seeds, but the E/S ratio was lower in large seeds than small seeds, showing more morphological dormancy part in large seeds than small seeds. In addition, E/S ratio also peaked in the fourth week of stratification, and after four weeks of stratification, the difference between E/S ratio was not significant. The small seeds have more physiological dormancy part than larger ones. Seed germination was significantly higher in large seeds than in small seeds. More than 70% of large seeds in both genotypes germinated without stratification. Thus, it can be concluded that larger seeds have less physiological dormancy part than smaller ones. To cultivate this medicinal plant, it would be beneficial to use large seeds to ensure a better germination and seedling establishment.