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Submitted to: Symposium Proceedings
Publication Type: Proceedings Publication Acceptance Date: 9/30/2010 Publication Date: 9/30/2010 Citation: Walters, C.T. 2010. Seed Longevity and deterioration in orthodox seed: A perspective based on structural stability of Visco-Elastic Materials. Symposium Proceedings IuFRO Tree Seed Symposium: Recent Advances in Seed Research and Ex Situ conservation, Taipei, Taiwan 16-18 August 2010. TFRI Extension Series No. 212: 1-8. Interpretive Summary: Problem: Early deterioration in seeds is asymptomatic for an unknown duration and then there is a period of catastrophic loss of seed viability. Unexplained variation in the duration of the asymptomatic phase within and among species, the lack of detectable symptoms of aging, and the long time taken to reach the threshold marking rapid mortality make it difficult to predict germplasm longevity. Moreover, viability models used to quantify aging rate under diverse conditions show exceptions to predicted behavior at moisture and temperature extremes and preclude prediction of when germplasm in genebanks should be monitored to confirm viability and regenerated before viability viability losses are realized. Accomplishment: This proceedings report reviews knowledge about seed quality factors and places the relationship between orthodox, intermediate and recalcitrant seeds into the context of biomechanical factors of the seed. A perspective that presents seeds as visco-elastic materials, and considers aging as a reaction that inextricably links structural and chemical stability, accounts for apparent temperature and moisture anomalies. A major consequence of this perspective is that moisture, temperature and seed quality interact to control the rate at which seeds age. Impact: The interaction of seed quality, moisture and temperature may explain the wide variation in seed longevity observed within and among species and ultimately lead to a mechanistic model that explains why, and accurately predicts when, seeds die during storage. Technical Abstract: Longevity of orthodox seeds during storage under controlled conditions can be estimated by mathematical models describing general temperature and moisture responses and accounting for variation within species by the initial seed quality. Despite the well-known trends, longevity of a particular seed lot is hard to reliably predict. Poor predictive power may result from our inability to adequately define initial seed quality and identify the traits associated with it. Or, reliable predictions may be limited because models do not fully account for anomalies in temperature and moisture response or interactions among factors. This paper presents seed deterioration as a problem of maintaining structural stability within the cytoplasmic matrix of seed cells as they dry and while they are stored. This perspective challenges a number of assumptions of the models used to define orthodox seed behavior. Concepts about visco-elastic behavior build from earlier concepts about the role of molecular glasses in seed longevity and provide a means to explain anomalous response to storage environment that distinguish orthodox from recalcitrant and intermediate behaviors. |
