WHEAT COLEOPTILE AND ROOT-GROWTH AND SEEDLING SURVIVAL AFTER DEHYDRATION AND REHYDRATION

Wheat (Triticum aestivum L.) seed frequently is planted deeply in dry soil that supports germination but not emergence. Our objective was to ascertain the effect of dehydration on seedling survival and developm ent, particularly the coleoptile and root, and their ability to resume growth after rehydration. Seeds of 'Larned', a tall, hard red winter wheat with a long coleoptile, were germinated for 1, 2, 3, 4, or 5 d a nd seedlings were dehydrated for 1, 2, 3, 4, or 5 d and then rehydrate d. Seedling survival was greater than 75% after 1 to 3 d germination a nd all dehydration treatments, but declined from about 60% to zero aft er germination for 4 d and dehydration for 3 d or more. Dehydration re duced coleoptile lengths by 17 to 58% compared with the control. Semin al roots also were highly sensitive to dehydration, except at early st ages, but were replaced quickly at all stages when seedlings were rehy drated. Changes in seed weight suggest that reserves were important fo r recovery of seedlings from dehydration. Increasing depth of planting and duration of germination successively reduced emergence of seedlin gs from seeds that were germinated for 1 to 4 d and then dehydrated fo r 2 d. The results demonstrated that emergence of wheat seedlings is i ncreasingly impaired by dehydration as germination progresses, that th e seedling stage when dehydration occurs is more important than the du ration of the stress, and that coleoptile and root growth and seed res erves are involved in seedling responses to dehydration.