Ethylene Evolution is Positively Correlated with Seed Vigor in Sweet Corn and Tomato Seed Lots with Differing Vigor Levels but Similar Germination Capacity

Sweet corn (Zea mays L.) and tomato (Lycopersicon esculentum Mill.) seeds were aged naturally for 18 months or artifi cially aged using saturated salt accelerated aging to provide seed lots that differed in seed vigor, but retained a high standard germination percentage. Seed vigor was confi rmed using standard vigor tests, including time to radicle emergence, cold, and accelerated aging tests. Ethylene evolution from both sweet corn and tomato seeds during germination was positively correlated with seed quality. Differences in ethylene evolution between nonaged and aged seeds were greater in seeds germinated on exogenous 1-aminocyclopropane-1-carboxylic acid (ACC). After 36 hours, there was about a 15-fold increase in ethylene evolution from seeds treated with 5 mM ACC compared to untreated seeds. Naturally and artifi cially aged seeds responded similarly and showed reduced ethylene production compared to nonaged seeds. In contrast to ethylene production, endogenous ACC titers were less for nonaged compared to aged seeds. Exogenous application of ACC to artifi cially aged seeds reduced the time to radicle protrusion, but did not completely reverse age-related effects on vigor. The data indicate that the reduced ability to produce ethylene in aged seeds was related to ACC oxidase (ACCO) synthesis or activity. Using Northern blot analysis, ACCO mRNA was detected after 48 hours of imbibition in nonaged seeds, but was undetectable in aged seeds affi rming the contention that ACCO synthesis was delayed or reduced by aging. The current study provides additional support for ethylene as a biochemical indicator of seed vigor in seed lots with reduced vigor but high germination capacity. triphosphate (ATP), and glutamic acid decarboxylase activity (GADA) tests. Biochemical tests for vigor are not routinely used by seed technology labs because of the complexity of the tests and an inconsistent correlation with seedling emergence. Ethylene is an easily measured volatile compound and appears to be ubiquitously produced in nondormant seeds following im- bibition with a sharp increase associated with radicle emergence (Matilla, 2000). The ability to evolve ethylene has been suggested as a seed vigor test (Khan, 1994). Numerous studies have shown a positive correlation between seed quality in diverse species and ethylene production (Gorecki et al., 1991; Ketring et al., 1974; Khan, 1994; Takayanagi and Harrington, 1971). These studies used natural or artifi cial seed aging to obtain deteriorated seed lots. In all cases, ethylene production was positively correlated with germination capacity. However, these studies evaluated seed lots with seed viability well below those acceptable for use by commercial seed companies. It is diffi cult to determine from these studies whether ethylene evolution was strictly associated with seed vigor or the seedʼs capacity to germinate. Therefore, the objective of this study was to determine if ethylene evolution was correlated with seed vigor in lots that differed in vigor as determined by standard physiological vigor tests, but retained similar standard germination percentages.