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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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H. K. Cahn, F. D. Moore III, and H. G. Hughes

Carbon dioxide concentrations measured within and above a strawberry plant (Fragaria × ananassa) canopy were significantly higher during enrichment with carbonated water or 900 kg CO2 ha-1 hr-1 applied as gas. Both sources were applied to the base of the plants through drip irrigation tubing under a black polyethylene mulch (0.025 mm) covering or over bare unmulched soil. Mulch affected the concentrations at the top of the strawberry canopy differently for the two sources of CO2 enrichment. Carbonated water was found to reduce the pH of the calcareous soil at the research site (pH 8.2) during and between irrigations. The greatest single pH reduction was 2.6 pH units during irrigation measured in mulched soil; significant soil pH reductions were detected as long as 28 days after irrigation underneath the mulch. Soil pH “duration” below pH 7.4 was 70% greater considering mulch and carbonated water vs. no mulch and carbonated water irrigation.

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F.D. Moore III, S.R. Nath, and Y-C Wang

Duration of growth is dependent on morphological events or changes in growth rate. It is the latter that is associated with phasic development. The most productive phase of plant growth is the linear or constant rate phase, primarily because it endures longer than the exponential phase. The purpose of our research was to objectively determine the true tree-height growth pattern, the linear and stationary phases of height growth, and to mathematically derive the maximum slope (maximum growth rate) of the growth curve, its location (inflection point), and the maximum slope of the logarithmic form (maximum relative growth rate) of the growth curve. The data were composed of 333 tree-height records covering 240 years from 200 beechwoods in the U.K. Height-age data were fitted using a splined function (S) and the Chapman-Richards function (CR). The growth curve and critical points on the curve were derived from the CR model. The linear phase began when trees were 9 and lasted 43 years. However, the stationary phase did not begin until age 162. Anecdotal evidence suggests that very little fruiting occurs before age 50. Based on derived critical points and anticipated source-sink dynamics, the reproductive stage should have taken place during the progressive “deceleration phase” when trees were between 31 (location of the maximum slope, also inflection point) and 162 (from quadratic root). The linear phase ended at 52 years, (coinciding with minimum acceleration) and may prove a more accurate estimate than 31. Maximum slope was 1.2 m per year occurring at age 31. Maximum slope of the log curve was 0.14 m·m–1 per year. The advantage of the CR function and the importance of the derived quantities and growth phases will be discussed.

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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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Jian Fang, E.E. Roos, C.T. Walters, and F.D. Moore III

Seed hydration and dehydration affects many physiological reactions, including priming, accelerated aging, and desiccation intolerance. Maize grains were repeatedly imbibed and desiccated, or imbibed and held for periods of time to identify the role of each of these factors. Grains were equilibrated to 12% moisture content (mc) and subjected to cycles (up to 14) of hydration (2 hours) and immediate dryback, or one hydration of 2 to 12 hours and dryback. Germination and vigor (root length and leachate conductivity) were determined after each cycle. Grains adjusted to three levels of hydration (27%, 34%, and 40%) were held for up to 10 days in a sealed desiccator. Each day samples were taken and either dried to the original mc prior to evaluation, or evaluated immediately as above. With each cycle of 2 hours of imbibition, seed mc increased (22% to 39%). Root lengths increased (priming effect) during the early cycles of imbibition and dryback. Decline in germination after eight cycles was a result of either accelerated aging or desiccation intolerance. Based on the results of the holding study, both factors contributed to deterioration, but desiccation intolerance was only observed when mc was above 27%. Conductivity of grain leachates was not correlated with loss of germination or vigor in whole grains, but appeared to reflect deterioration in isolated embryos.

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Jian Fana, E.E. Roos, C.W. Vertucci, and F.D. Moore III

Seed water content has been considered the most important factor controlling various physiological reactions in seeds. Hydration/dehydration affects many physiological reactions, including the “priming effect” and “accelerated aging,” depending on time and level of hydration. Corn seeds (11% mc) were subjected to six cycles of hydration (2 h) and dryback or one hydration of 12 h and dryback. Following soaking, seeds were dried quickly by using a fan to remove moisture and then equilibrated to their initial mc. Seeds were evaluated for germination and vigor (root length and leachate conductivity). Percent germination of seeds treated with either continuous or intermittent hydration and dehydration was >90%. Vigor of seeds hydrated for successive 2-h cycles initially increased (priming effect); however, after the sixth cycle, vigor was equal to the nontreated control seeds. One cycle of hydration for 12 h then dryback had no effect on germination but did increase vigor. We are now extending the number of 2-h hydration periods to 10 to determine when damage occurs from these cycles. Our objective is to better understand the relationship between seed hydration and physiological changes associated with seed priming, accelerated aging, and imbibition damage.