.Effect of Ageing on Onion (Allium cepa L (Seeds Quality (Germination and Vigour

Abstract

This study was conducted in the laboratory of the Seed Administration, Federal Ministry of Agriculture and Forestry, Khartoum Sudan, to show the effect of normal and accelerated ageing (AA) on onion seed quality. Seed samples were drawn according to the International Seed Testing Association (ISTA, 1999) from four seed lots produced in four consecutive seasons (2004, 2005, 2006 and 2007) and stored in a normal store room under normal storage conditions. According to their production season, they are considered to be of four ages (one, two, three and four years old, respectively).The seed samples were tested in two experiments. The first one was for testing the effect of normal aging and the second one for testing the effect of AA, on seed quality. The AA treatment were done according to Matthew and Powell,(1981) where the seed moisture content (SMC) was increased from the initial moisture content (5% SMC) to 10, 12.5 and 15 %, and dried again to 5% at 45oC for 48, 72 and 96 hours (accelerated aging durations (AAD), respectively. Both germination and emergence (vigour) and their attributes (germination percentage, mean germination time, germination homogeneity, emergence percentage, mean emergence time and emergence homogeneity, respectively) were evaluated. For both experiments the germination and its attributes were evaluated after growing the seeds on filter paper in Petri dishes under controlled conditions, where as the IV emergence and its attributes were evaluated after growing the seeds in sand in plastic pots under room conditions. The experimental units of both experiments were distributed in a complete randomized design (CRD) with four and three replications, respectively. The results showed that ageing has significant effect on both germination and emergence (vigour) and their attributes) of onion, especially if the seeds were above two years old. The interactions between normal and AA were significant, especially at 12.5 % SMC and 72 hours AD at 45oC. Seeds more than two years old had almost lost their vigour at this AA treatment. The highest AA (15% SMC and 96 hours AD) led to a complete seed deterioration. It could be concluded that onion seeds quality decreased significantly after two years age and above three years age would lose vigour and may be of no commercial value as seed . AA treatment of 12.5%SMC and 72 hours AD may be suitable as vigour test of onion seed lots of two years age and the relatively lower AA treatment (10% SMC and 48 hours AAD) for older seed lots (above two years old) because a higher SMC and a longer AA (12.5 % and 72 hours, respectively) may increase the effect of temperature and may be conducive to fungal growth and so accelerated seed deterioration.