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K.G.V. Davidson, F.D. Moore III, E.E. Roos, S. Nath, and S. Sowa

Five seed-quality indices based on individual seed electrolyte leakage tests were evaluated. Zea mays L. seeds were soaked for 6 hours, and individual seed leachate conductivity values were obtained. A total of 100 cells were scanned, one seed per cell, at 5-minute intervals for the first 30 minutes, followed by 15-minute intervals for the remaining 330 minutes. Seeds were allowed to dry for 5 to 7 days at room temperature and then were tested for germinability at 25C for 7 days. Radicle lengths were measured after 72 hours. The Richards function was fitted to cumulative frequency distributions of μAmps to obtain internal slope (IS), mean μAmp, and median μAmp values for each scan. Initial leach rate (ILR) was estimated after fitting hyperbolic functions to μAmp vs. soak time data. Average leach rate (ALR) was also derived from fitting the Richards function to μAmp vs. soak time data. Linear regression of seed quality on IS, mean, and median μAmp values after 5 hours of imbibition yielded r2 values of 0.91, 0.81, and 0.86 for predicting viability and 0.56, 0.46, 0.52 for predicting radicle length. Thus, IS was the best seed quality predictor, followed closely by median and mean μAmp values. ILR and ALR were not correlated with seed quality.

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K.G.V. Davidson, F.D. Moore III, and E.E. Roos

Multiple electroconductivity readings (μAmps) of leachates from individual seeds during the first 6 hr of imbibition was examined as a possible predictor of seed quality. Readings from each sample of 100 seeds were formed into frequency distributions and the mean, median. and internal slope were calculated using an automated computer retrieval system. Internal slope is a non-central tendency measure based on the slope of a line tangent to the inflection point of the S-shaped cumulative frequency distribution (CFD) of μAmps. Radicle lengths (3 days) and germination (7 days) percentages were regressed on each of the two measures of central tendency and also the CFD shape indicator, internal slope. None of the three predictors were satisfactory for estimating seed vigor (root lengths) of maize (Zea mays L.) or wheat (Triticum aestivum L.) or germination of wheat seed lots. Internal slope was useful in estimating viability of artificially aged maize seeds (r2= 0.91), which compared favorably with our previous results using naturally aged red clover (Trifolium pratense L.) seed lots. Overall the seed quality of the unaged wheat lots was fairly high and the electrolyte leakage test was not sensitive enough to detect differences within these lots.

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F. D. Moore III and E. E. Roos

An index “internal slope” derived from the cumulative frequency distribution of individual seed leachate conductivities is related to seed quality; the larger the index value the less variation among individual seeds in a sample (100 seeds) and the higher the seed quality. We have recently developed data acquisition/instrurment control/data smoothing/data analysis software which accesses frequency and cumulative frequency distributions of individual seed conductivities and the derived index on an almost continuous basis from the start of the first soaking.

At present, lack of convergence with regard to curve fitting may occur necessitating multiple sampling times. A “window in time” approach is described whereby index estimates during a two-hour interval within the index stability phase are averaged. Evidence of the method's ability to assess seed vigor will be presented.

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Rebecca L. Turk, Helen T. Kraus, Ted E. Bilderback, William F. Hunt, and William C. Fonteno

1.8 m wide × 9.8 m long × 1.2 m deep with a substrate volume of 15.3 m 3 . A 0.9-m raised berm covered with weed fabric was built between each bed. Rain gardens were dug to have a slight internal slope of 2%. Before filling each rain garden, a 10