Role of Pericarp in Reducing Spinach (Spinacia oleracea L.) Seed Germination at Supra-optimal Temperatures

Abstract

Germination of the spinach (Spinacia oleracea L. var. grabra cv. Nobel) seed was examined at supra-optimal temperatures. Almost all seeds germinated rapidly at 20 degrees C. However, germination decreased as temperature was raised and fell to about 10% at 35 degrees C. Removal of the pericarp as well as presoaking treatment markedly improved germination, especially at 35 degrees C. Germination of pericarp-removed seeds was inhibited by water soluble extracts from seeds and pericarp, but not by those from presoaked seeds. The inhibitory activity of the extracts was not affected much by incubation temperatures before extraction. Sulphuric acid treatment conducted to modify the physical properties of the pericarp and hydrogen peroxide treatment conducted to elevate the oxygen tension promoted germination. Thus, the poor germination at high temperatures may be caused mainly by the pericarp, which produces germination inhibitors or gives mechanical resistance and impermeability to gases. Even in the pericarp-removed seeds, germination was delayed at high temperatures, indicating that high temperature directly affected the embryo.