Production of high quality seed corn (Zea mays L.) would be facilitated by the harvesting of the seed at a kernel maturity which is highly correlated with maximum seedling vigor. This study attempted to correlate several kernel maturity indices with measures of seedling vigor in a maturing seed corn crop.Hybrid seed samples were taken from two field locations of production of maternal parents ‘A632’, ‘Va26’, ‘B73’, and ‘Mo17’ from 35 days to 98 days after silking. Kernel maturity indices evaluated were: 1) fresh kernel respiration rates, 2) black layer development, 3) moisture percentage, and 4) dry weight accumulation. After drying, the seed was grown on moistened, rolled paper towels in the dark for seven days at 25 C. Vigor measurements included germination percentage, shoot dry weight, and root dry weight. Although germination percentages were high over all harvest dates, both shoot and root dry weight were highly dependent on date of harvest. Distinct vigor maxima and minima were noted, and the first and last sample dates never corresponded to maximum shoot and root dry weight. Dates of maximum vigor and kernel maturity patterns were specific for each hybrid. Maximum kernel dry weight was correlated with maximum shoot and root dry weight, and the range of kernel moisture percentage corresponding to initial attainment of maximum kernel dry weight was small.
Our purpose is to examine statistical methods, particularly field plot technique, hypothesis testing, and inference suggesting, from a seed corn (Zea mays L.) company viewpoint. Company managers must look beyond traditional statistical methods to develop systems that identify superior new products. These systems should mimic the processes used by farmers in selecting new hybrids that provide superior performance in the broad range of environments where they will be grown. This paper shows the evolution of seed company strategy to identify superior hybrids in product development and testing systems. Test resource allocation has changed to fewer replicates per location, to more locations per year, to more years per hybrid comparison, and to more data integration across test types. Experimental design has changed from sophisticated to simple designs, from experiment summaries to head‐to‐head comparisons (two hybrids compared in all tests in which both were grown) then to head‐to‐group comparisons (series of head‐to‐head comparisons for a hybrid with appropriate elite hybrids within a maturity group), and from analyses of variance to t‐test analyses. Stability regressions have become more popular. As improved statistical methods have been used, more genetic progress per unit of time has resulted; hybrids have become more stress tolerant, thus more widely adapted.
Genetic vulnerability of corn (Zea mays L.) has increased repeatedly since the growing of hybrid corn, single cross hybrids, and popular hybrids. We definite genetic vulnerability as the potential susceptibility of a crop to future attack by some biological or environment stress due to growing large numbers of a uniform biotype over large geographical areas. Genetic diversity, which usually decreases genetic vulnerability, has lacked a good method for measurement. The purpose of this study was to develop and test a method for measuring genetic diversity of corn and to assess genetic vulnerability in the U.S. Corn Belt by comparing genetic diversity of popular hybrids between two major and seed companies. Genetic diversity was estimated by the formula: GD = 1‐[(H‐C)/(H‐S)], where GD equals genetic diversity, H equals the average performance of the two hybrids, C equals the hybrid‐by‐hybrid cross, and S equals the average of the selfed hybrids. The method assumes heterosis is caused by some degree of dominance and epistasis is absent. A higher than average performing cross of two hybrids (less inbreeding depression) indicates more genetic diversity between the hybrids while lower than average performance of the cross (more inbreeding depression) indicates less diversity. Data were collected for grain yield, time to flower, grain moisture, and plant height on five popular hybrids from each of two major seed companies. Results for yield provided more precise estimates of GD than other performance traits measured. Genetic diversity averaged 0.74 and ranged from 0.17 to 1.37 and 0.28 to 1.12 among hybrids within companies. The GD estimate for the two most popular hybrids of 1985, 3732 and T1100 was 0.94. Our results help those needing a method to measure genetic diversity and should also encourage those concerned about genetic vulnerability in corn.
In soybeans (Glycine max (L.) Merr.) an epigeal emerger, the sole seedling organ responsible for elevating the cotyledons and epicotyl to the soil surface is the hypocotyl. Yet, soybean seedling and, in particular, hypocotyl growth under field conditions have not been well studied.We measured hypocotyl length and swelling index (mg fresh weight/cm length) of several cultivars and two seed sizes at several planting dates and depths. Genetic variability was found in these two measurements. Cultivar differences in hypocotyl length generally followed the “long” and “short” hypocotyl classification of cultivars based on hypocotyl growth at 25 C. Hypocotyl swelling‐index differences generally were independent of the “long” and “short” cultivar classification. Hypocotyl length was highly correlated with rapidity of emergence, whereas hypocotyl swelling index was not highly correated with this measurement. Small seed of ‘Amsoy 71’ and ‘Corsoy’ produced seedlings with longer hypocotyls than did large seed, but there was no effect of seed size on hypocotyl length in ‘Wayne’. Small seed of all cultivars produced seedlings with lower values of hypocotyl swelling‐index than did large seed. Depth of planting significantly affected hypocotyl length and swelling index, but the specific soil factors affecting these two measurements were not identified. The consistently larger values of hypocotyl swelling index at deep as compared with shallow plantings, as web as the relatively large values for this measurement in the field as compared with those obtained in the laboratory, suggested that soil resistance is one limiting soil factor.
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