25 Mannitol Priming Induces Biochemical Changes and Enhances Germination Capacity and Seedling Vigor in Marigold (Tagetes spp.) I. Afzal 1 , S. Ashraf 2 , M. Qasim 2 , S.M.A. Basra 1 , M. Shahid 3 and B. Hussain 1 1 Department of Crop Physiology, University of Agriculture, Faisalabad, Pakistan 2 Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan 3 Department of Biochemistry, University of Agriculture, Faisalabad-38040, Pakistan Keywords: seed priming, mannitol, emergence, α-amylase, African and French marigold Abstract Marigold is one of the important annual flowers grown for commercial purposes all over the world. A fast decline in vigor and viability of marigold seeds is a main problem under ambient storage conditions. Little information has been reported on seedling development of marigold subsequent to priming. Therefore, a laboratory study was carried out to investigate the influence of priming with mannitol (2, 4 and 6%) on germination and seedling growth of African and French marigold seeds. Priming with 2 and 4% mannitol for 24 h maximally increased final germination percentage, germination capacity, germination index, shoot and root lengths of both marigold species as compared to all pre-sowing seed treatments including control. Similarly, at those concentrations mannitol significantly reduced mean emergence time and days to 50% emergence, increased seedling emergence uniformity, final seedling emergence percentage and seedling growth. In conclusion, priming with 2% mannitol proved to be the most effective priming agent in both marigold cultivars. This could be attributed to the effect of mannitol in increasing reducing and total sugars as well as α-amylase activity in primed seeds. INTRODUCTION Marigold is grown as ornamental crop for cut flowers and as a landscape plant throughout the world. African marigold petals are commercially valuable as a natural source of xanthophyll pigments used primarily in poultry industry to intensify yellow colour of egg yolk (Kaul et al., 2000). Due to market demand in recent years, there has been increasing interest in cultivation of this plant. But, the emergence and stand establishment of marigold seeds are often slow and extremely erratic, particularly under hot or cool field conditions. Seed priming (controlled hydration followed by redrying) has been used to reduce germination time, synchronize germination, improve germination rate and crop establishment in many crops under suboptimal temperatures (Yoon et al., 1997; Afzal et al., 2008). Primed seeds germinate in a wider range of temperatures (Bray, 1995) and are less sensitive to oxygen deprivation (Corbineau et al., 1993) than unprimed ones. Limited work has been reported regarding biochemical and physiological changes induced by mannitol priming in marigold seedlings. Therefore, this study was carried out to investigate the potential of mannitol as priming agent on enhancing germination capacity and seedling growth of marigold species and to determine levels of total sugars and α- amylase activity as biochemical indicators. MATERIAL AND METHODS Seeds of African marigold (Tagetes erecta L.) and French marigold (Tagetes patula L.) cultivars were soaked in aerated solution of solution of 2, 4 and 6% mannitol separately for 24 h at 25±2°C in dark and then spread in a thin layer on dry filter paper and dried for 2 d at 30°C until the initial seed weight (Bradford, 1986). Four replicates of 25 primed or non-primed seeds were germinated in 9 cm diameter petri dishes (for 10 days) and in plastic trays (for 25 days) under continuous fluorescent light at 25°C in a growth chamber (Vindon, England). Germination and emergence parameters were calculated as described in the Association of Official Seed Proc. V th IS on Seed, Transplant and Stand Establishment of Hort. Crops Eds.: J.A. Pascual and F. Pérez-Alfocea Acta Hort. 898, ISHS 2011