Responses ofIpomoeaspp. and Smallflower Morningglory (Jacquemontia tamnifolia) to Temperature and Osmotic Stresses

Abstract

Seed germination responses to temperature and osmotic stress were determined for smallflower morningglory [Jacquemontia tamnifolia(L.)Griseb.] and seven species ofIpomoea.Cypressvine (I. quamoclitL.), willowleaf (I. wrightiiGray) and smallflower morningglory germinated and seedlings developed more slowly than the other morningglories at 16 C. Maximum germination of ivyleaf [I. hederacea(L.), Jacq. var.hederacea], entireleaf [I. hederacea(L.) Jacq. var.integriusculaGray], pitted (I. lacunosaL.), tall [I. purpurea(L.) Roth], cotton (I. trichocarpaEll.), and smallflower morningglories occurred in 24 h at 20 C. Cypressvine and willowleaf morningglories reached maximum germination in 24 h at 24 C. Optimal root-hypocotyl development occurred at 24 C for pitted, tall, and willowleaf morningglories, while all other species required a temperature of 28 C for maximal root-hypocotyl development in 4 days. Increasing osmotic pressure decreased or delayed germination of all morningglory species. Species tolerance to osmotic stress during germination could be ranked, most to least tolerant, as follows: ivyleaf=entireleaf>pitted=cotton>tall = willowleaf>cypressvine=smallflower. Maximum germination was delayed approximately 24 h for each 2 bar increment increase in osmotic pressure.