Survival characteristics of corn seed during storage. I. Normal distribution of seed survival

Understanding the survival characteristics of hybrid corn (Zea mays L.) seed during storage is necessary to predict seed deterioration. This investigation tested one key assumption of the Ellis and Roberts viability equation, namely, that seed survival is normally distributed. Eleven corn seed lots (six hybrids) with little mechanical injury and a wide range in initial vigor were stored in various combinations of constant temperatures (20, 30, 40, and 50 degrees C) and seed moisture contents (100, 120, 140, and 160 g kg(-1), fresh weight basis). Seed-survival curves were constructed by conducting successive germination tests at frequent intervals during storage. The chi-square goodness-of-fit test was used to evaluate the normality of survival curves constructed from either full or truncated (germination between 95 and 5%) data sets. When the data were truncated, the majority (79%) of the 187 survival curves analyzed were classified as normal (P > 0.05) or near-normal [P < 0.05 but relatively small chi-square, heterogeneity factor (H = chi-square/df) < 10]. Only 57% of the curves from the full data set followed a normal or near-normal distribution. Seed moisture and storage temperature had no consistent effect on the shape of the survival curves. Survival of low-vigor seed lots was more likely to be normally or near-normally distributed than was survival of high vigor seed lots. The assumption that seed survival is normally distributed was generally valid for truncated data sets of hybrid corn seed in constant storage environments.