INTERNATIONAL JOURNAL OF AGRICULTURE & BIOLOGY 1560–8530/2004/06–4–708–711 http://www.ijab.org Loss of Vigour and Viability in Aged Onion (Allium cepa L.) Seeds M. MUMTAZ KHAN 1 , M. JAVED IQBAL, M. ABBAS, H. RAZA, R. WASEEM AND ARSHAD ALI† Institute of Horticultural Sciences, University of Agriculture, Faisalabad–38040, Pakistan †Department of Agricultural Extension, University of Arid Agriculture, Rawalpindi–Pakistan 1 Corresponding author’s e-mail: mumtaz59pk@hotmail.com ABSTRACT Onion (Allium cepa L.) seeds exhibit very short life and loose their viability within 1-2 years. Accelerated ageing studies were conducted on indigenous onion cv. “Desi Red” to investigate the vigour and viability in relation to germinability and seed membrane damage. Seed lost their germinability, vigour and viability progressively with ageing treatment. Germination percentage reduced up to 43%, radicle length 1.7 cm and germination speed 6.68 (GSI). Time to get 50% germination and electrolyte leakage increased significantly (p<0.05) with the ageing time and treatment. While the leaching from viable seeds (control) was negligible. The loss of viability in seeds after ageing appeared related to increased membrane destruction (loss of membrane integrity). This membrane integrity loss may be responsible for the decreased germinability, vigour and ultimately viability. Key Words: Onion (Allium cepa L.); Germinability; Vigour; Membrane destruction; Viability INTRODUCTION Many farmers know from experience that seed of same lots may emerge from the soil quite differently, resulting in erratic field stands, replanting (on some occasions), or both. Vigorous seeds will produce excellent emergence and stands in proper soil environment. It can improve the chances for satisfactory emergence. Advanced stages of seed deterioration are evidenced by visible symptoms during germination and seedling growth. However, these are preceded by more subtle physiological changes whose symptoms can be detected only by sophisticated measurement techniques. Quality seed is defined as varietally pure with a high germination percentage, free from disease and disease causing organisms, and with a proper moisture content and weight. Vigour is often implied when discussing seed quality and most growers have to use the terms quality and vigour interchangeably. Seed vigour comprises those properties, which determine the potential for rapid uniform emergence and development of normal seedlings under a wide range of field conditions (ASPB, 2003). Seed vigour is generally related to yield in vegetables. Studies have shown that this vigour test functions well in forecasting field emergence and stand establishment in a wide range of crop species. In general, when seeds are planted under stressful field conditions, provides higher correlations with field emergence than does standard germination (Pandey et al., 1990). Subsequent studies have verified that accuracy of this test in predicting the life span of a number of different species under a range of storage conditions. The performance capabilities of many seeds deteriorate during prolonged storage, but the rate of deterioration varies greatly among species (Robert, 1989). High temperature, ambient relative humidity, and seed moisture content are the main factors influencing seed storage capability (Abdul-Baki, 1980). The degree of cell membrane damage in response to ageing can be measured in terms of rate of seed electrolyte leakage (Larson, 1968; Simon, 1978; Khan et al., 2003). Damage to the organization of cell membranes during seed ageing may constitute an important factor in explaining seed deterioration (Senaratna et al., 1988; Ferguson et al., 1990). In order to obtain information on seed vigour in a timely manner, the accelerated ageing technique is commonly used, through which changes in the seed at the cellular level during long-term storage can be simulated within a comparatively short period of time by exposing seeds to increased temperatures (40-45 o C) and a high relative humidity (Abdul-Baki, 1969; Delouche & Baskin, 1973). The accelerated aging test is rapid, inexpensive, simple and useful for many species; it can be used for individual seed evaluation and requires no additional training for correct evaluation. Solute leakage accompanies seed imbibition during the process of membrane reorganization following re-hydration. The rate of leakage depends on the degree of cell membrane damage in response to ageing (Larson, 1968; Simon, 1978). Damage to the organization of cell membranes during seed ageing may constitute an important factor in explaining seed deterioration (Priestly & Leopold, 1979; Senaratna et al., 1988; Ferguson et al., 1990; Khan et al., 2003). Onions are one of the oldest vegetables in continuous