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Ultra dry seed storage was studied in onion (Allium cepa L.) and china aster [Callistephus chinensis (L.) Nees] to find out its effect on seed longevity under ambient and controlled low temperatures. Seeds of onion cultivars Arka Kalyan and Arka Niketan ultra dried to 2.8 and 2.6 %, respectively, and seeds of china aster cultivar Arka Kamini ultra dried to 3.0% were compared with seeds of respective cultivars having moisture content close to recommended levels for packing in moisture proof containers. These seeds were hermetically sealed in aluminium pouches and stored at ambient and controlled (constant 15°C) temperatures. The initial germination in onion was 90.0 and 88 % in Arka Niketan and Arka Kalyan, respectively, and it remained unaffected after ultra drying. During storage, ultra dry seeds and seeds with ~5% moisture content of both varieties showed no significant reduction in seed germination, first count, seedling vigour and field emergence even after 54 months of storage both under ambient and controlled temperatures. In china aster, seeds with 5.9% moisture showed decline in seed viability and vigour under ambient temperature after 18 months of storage and rapid decline was noticed after 24 months of storage, reaching zero at 36 months but at 15°C showed no decline in viability up to 48 months of storage. Ultra dry seeds maintained higher viability and vigour at both ambient and at 15°C even after 48 months of storage. Genetic fidelity tests on onion seed clearly demonstrated that neither the profiles of soluble proteins and enzymes nor the DNA were affected by ultra drying.