The Ellis‐Roberts deterioration model depends on the assumption that the rate of seed deterioration is the same among seed lots of a crop species when stored in identical environments. The rate of deterioration of 11 corn (Zea mays L.) seed lots from six hybrids was measured during storage in various combinations of constant temperatures (20, 30, 40, and 50°C) and seed moisture contents (100, 120, 140, and 160 g kg−1, fresh weight basis). The seed‐survival curves were constructed by conducting successive germination tests at frequent intervals during storage. The rates of seed deterioration were estimated by probit analysis and differences among seed lots were identified by analysis of variance. The deterioration rates were significantly different among seed lots in 16 of 21 storage environments when analyzing full data sets (all data points) and in 14 of 21 storage environments when using truncated data sets (germination percentages between 5 and 95%). Both genotype and initial seed quality affected the rate of deterioration with low‐vigor seed lots generally deteriorating at a faster rate than high‐vigor seed lots. The rate of deterioration was greatly influenced by storage environment and increased with an increase in storage temperature, seed moisture, or both. The assumption of a constant rate of seed deterioration in identical storage environments was not valid for hybrid corn seed.

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The Ellis‐Roberts deterioration model depends on the assumption that the rate of seed deterioration is the same among seed lots of a crop species when stored in identical environments. The rate of deterioration of 11 corn (Zea mays L.) seed lots from six hybrids was measured during storage in various combinations of constant temperatures (20, 30, 40, and 50°C) and seed moisture contents (100, 120, 140, and 160 g kg−1, fresh weight basis). The seed‐survival curves were constructed by conducting successive germination tests at frequent intervals during storage. The rates of seed deterioration were estimated by probit analysis and differences among seed lots were identified by analysis of variance. The deterioration rates were significantly different among seed lots in 16 of 21 storage environments when analyzing full data sets (all data points) and in 14 of 21 storage environments when using truncated data sets (germination percentages between 5 and 95%). Both genotype and initial seed quality affected the rate of deterioration with low‐vigor seed lots generally deteriorating at a faster rate than high‐vigor seed lots. The rate of deterioration was greatly influenced by storage environment and increased with an increase in storage temperature, seed moisture, or both. The assumption of a constant rate of seed deterioration in identical storage environments was not valid for hybrid corn seed.

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in any environment. The development of quantitative models culminated with the viability equation (Eq. [1]) An assumption of the Ellis-Roberts viability equation, that all seedof Ellis and Roberts (1980a) lots of a species deteriorate at the same rate in the same storage environment, was not valid for hybrid corn (Zea mays L.) seed. Thus,[1]an alternative model was developed that used a potential storability index (P G , the time for germination to decline to a level G ) and awhere v is the probit or standard normal equivalent storage environment coefficient (SEC, the factor by which seed londeviate of germination (%), K i is the initial seed lot gevity is altered by a change in storage temperature and seed moisture constant (on the probit scale), p is the storage period content) to predict deterioration of hybrid corn seed. The alternative (days), m is moisture content (%, fresh weight basis), t is model was derived from the ratio of seed longevity of the same seed temperature (ЊC), and K E , C W , C H , and C Q are constants lot in two storage environments. The P G in the storage environment having common values for all seed lots of a species. was estimated as the product of P G in a rapid-aging test and SEC, which was determined with a regression model based on the differences in The significant characteristics of this equation are the temperature and moisture between the two environments. The model inclusion of initial seed quality, storage temperature and was evaluated by predicting the time to 90 and 50% germination (P 90 seed moisture. Equation [1] has been evaluated in a and P 50 ) for high-and medium-quality seed lots stored under a rangenumber of crop species (Ellis and Roberts, 1980b, 1981; of constant conditions. There was generally good agreement between Ellis et al., 1982; Kraak and Vos, 1987; Ellis, 1988; Tepredicted and observed P 90 and P 50 , with many of the predicted values Krony et al., 1993; Fabrizius et al., 1999) and is depenwithin 10% of observed values across five seed lots. The storage dent on two key assumptions: normality of distribution conditions in the rapid-aging test had no effect on the predictive of seed deaths with time and a constant rate of seed ability of the model. This model provides an effective approach to predicting corn seed longevity that may be useful in managing seed deterioration for all seed lots within a species stored in storage.identical conditions. The failure of seed survival to be normally distributed has been reported for several crop species (Moore and S. Tang, RiceTec, Inc., P.O. Box 1305, Alvin, TX 77512; D.M. Tewas expressed as equilibrium relative humidity (Ellis et