ORIGINAL PAPER Effect of post-irradiation ageing on onion seeds Muhammad Amjad Æ Muhammad Akbar Anjum Received: 23 December 2005 / Accepted: 9 May 2006 / Published online: 28 November 2006 Ó Franciszek Go ´ rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´ w 2006 Abstract Seeds of onion (Allium cepa) cv. Ailsa Craig were exposed to various doses of gamma radia- tion (0, 10, 20, 40, 80 and 100 krad) and subjected to accelerated ageing (RH 100%, 42°C) for 12 h. Radia- tion doses significantly affected the percentage of normal seedlings, abnormality types (%) and seedling growth. Seed viability, conductivities of seed leachates, final germination (%), germination speed and time to reach 50% germination (T 50 ) were not affected by the seed irradiation. Accelerated ageing after irradiation had significant influence on seed viability, conductivi- ties of seed leachates, final germination (%) and per- centage of normal seedlings. Germination speed, T 50 and seedling growth were not affected by the acceler- ated ageing. However, all the parameters studied were significantly influenced by the interaction of radiation doses and accelerated ageing. Accelerated ageing generally enhanced the damaging effects of irradiation on seeds. Therefore, it was concluded that onion seeds should not be exposed to adverse environmental con- ditions after irradiation. Keywords Allium cepa  Onion  Seed irradiation  Accelerated ageing  Germination potential  Seedling growth  Seed viability Introduction Gamma radiation has widely been used to enhance the storability of grains and legumes, improve seed ger- mination, increase yield and quality of produce, and to induce genetic variability in crop plants (Anjum et al. 1990; Ripa and Audrina 1993; Munishamanna et al. 1998; Latha and Nair 1999; Selim and El-Banna 2001; Viccini and Carvalho 2001). High doses of gamma radiation produce deleterious effects, such as poor growth and genetic damage. Relatively low doses usually alter growth characteristics, whereas very low doses have been shown to stimulate plant growth (Watanabe et al. 2000). However, radiosensitivity varies from species to species and even among geno- types of the same species (Ahmad and Qureshi 1992; Feng 1996; Kumar and Chaudhary 1996). Gamma radiation interferes with the process of cell division, resulting in cytological abnormalities. Therefore, fre- quency of dividing cells is affected, culminating into altered growth and morphological variability. Damag- ing effects of irradiation on seed depends upon various factors including physiological condition of seed, irra- diation dose, dose rate, etc. Storage of seed after gamma irradiation may lead to genetic repairing (Mishra and Raghuvanshi 1988). According to Punjabi and Basu (1982), hydration–dehydration of seeds be- fore or soon after irradiation considerably minimized the adverse effects of irradiation on germinability and root growth. They also found that hydration–dehy- Communicated by M. Horbowicz. M. Amjad Institute of Horticultural Sciences, University of Agriculture, Faisalabad 38040, Pakistan M. A. Anjum University College of Agriculture, Bahauddin Zakariya University, Multan 60800, Pakistan M. A. Anjum (&) Pakistan Council for Science and Technology, Shahrah-e-Jamhuriat, G-5/2, Islamabad, Pakistan e-mail: anjumbzu@yahoo.com; anjumbzu@hotmail.com 123 Acta Physiol Plant (2007) 29:63–69 DOI 10.1007/s11738-006-0010-5