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Matthew D. Kleinhenz

A total of 21 and 28 standard and experimental varieties of yellow and white se- and sh2-type sweet corn (Zea mays) were planted in 1999 and 2000 in Fremont and Wooster, Ohio, which are separated by 193.1 km (120 miles) and contain different soil types. Data are reported here for a subset of these varieties (eight yellow, two white) showing a consistently high level of use in Ohio and planted in both years. Endosperm types were planted in distinct, parallel experiments separated by a minimum of 79.9 m (262 ft) at each site. A randomized complete block design with four replications per variety (V) per location (L) was used, with measures of 13 production- and market-based variables taken from emergence to 48 hours after harvest. Soluble solids 48 hours after harvest were greater at Wooster than Fremont in the sh2 study. Variety had a significant, independent effect on mean plant and ear height in the se and sh2 study, respectively, although further analysis of year × variety (Y × V) and location × variety (L × V) interactions suggested that V affected additional traits. On average, `Tuxedo' (se) and `HMX6383S' (sh2) had superior com-binations of grower- and consumer-oriented traits. However, varieties with the highest levels of percent emergence and marketable yield tended to have lower levels of soluble solids, regardless of endosperm type. Y × V interactions were primarily due to changes in the magnitude of values for individual varieties in each year, not from changes in their relative ranking. The Y × L × V interaction was significant (P ≤ 0.05) for marketable yield, plant and ear height, and the ratio of ear length to diameter in the se study, but zero variables in the sh2 study. Coefficients of determination (R 2) for selected plant and ear traits were unaffected by location. Overall, R2 values ranged from 0.04 (number of rows of kernels × ear diameter, sh2 study) to 0.83 (shank length × total ear length, sh2 study). These data reinforce that genetics strongly affect key traits in sweet corn and identify two potential top performers. The data also suggest that independent L or L × V effects may be minor relative to V effects, even when locations are separated by moderate distances and contain different soil types. Therefore, including more varieties but fewer sites may be warranted in future variety trials. The data also suggest that 1) ratings of variety performance should be based on objective measures of grower- and market-oriented traits and 2) shank length × total ear length and ear height × plant height relationships may be used to improve the efficiency of future evaluations.

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Brian A. Kahn and Niels O. Maness

-1, G-2, and G-3, respectively. A completely randomized experimental design with five replications was used for each of the three GA experiments. Data were subjected to analysis of variance procedures. Main effects of row number and seeding rate

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D.C. Sanders and W.R. Jester

During 2 years, `Takinogawa Long' gobo was seeded with two, three, or four rows per 1.5-m bed at in row spacings of 7.5, 15, 21.5, and 30 cm. Total and marketable yield increased with in-row spacing and marketable yield increased with row number, with greatest yields occurring at 15 cm regardless of row number. Average root weight and yield of forked roots were not affected by row number but increased with in row spacing. Similarly, percent forked roots decreased with more rows per bed. The 15-cm in-row spacing had the greatest yield, but also the greatest weight of culled roots, but none of the populations affected percentage culls. In another study, in-row subsoiling (SS) and in-row banded phosphorus (P) were evaluated. Marketable yield was increased by both SS and P but did not interact. P increased average root weight. Neither SS or P affected forked root yield or cull root yield, but SS decreased forked roots and increased cull production.

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D.C. Sanders, Jay Frick, and W.R. Jester

`Takinogawa Long' gobo was seeded with two, three, or four rows per 1.5-m bed at in-row spacings of 7.5, 15, 21.5, and 30 cm. Total and marketable increased with in-row spacing and marketable yield increased with row number with the greatest yields occurring at 15, regardless of row number. Average root weight and yield of forked roots was not affected by row number, but increased with in row spacing. Similarly, percentage of forked roots decreased with more rows per bed. The 15-cm in-row spacing had the greatest yield, but also the greatest weight of culled roots, but none of the populations affected the percentage culls. In another study, in-row subsoiling (SS) and in-row banded phosphorus (P) were evaluated. Marketable yield was increased by both SS and P, but they did not interact. P increased average root weight. Neither SS or P affected forked root yield or cull root yield, but SS decreased forked roots and increased cull production.

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David B. Rubino and David W. Davis

This study was conducted to investigate the effects of mild mass selection for adaptation on the performance, genotypic variance, combining ability, S1 family-testcross correlation, and midparent heterosis of S1 families derived from a sweet corn (su) × tropical maize (Zea mays L.) composite (Composite 1R). Four cycles of random mating followed by 10 cycles of 10% stratified mass selection were conducted for earliness, plant and ear type, and freedom from pests. Selection significantly (P < 0.01) decreased plant height, ear height, percentage barrenness, and ear length, and significantly (P < 0.01) increased stalk breakage, earliness (Celsius heat units to 50% anthesis and silking), and kernel row number of both S1 families and their testcrosses. Juvenile plant height at 45 days after planting increased in testcrosses only. Percentage tip blanking and pericarp thickness did not change. For most traits, the greatest response occurred during the first five of 10 selection cycles. Cycle 10 testcrosses performed at least as well as elite check testcrosses for eight of 10 traits. The tropical parents improved combining ability for increased juvenile plant height and kernel row number, and decreased percentage of stalk breakage. As a result of selection, genotypic variance among S families decreased by >40% for heat units to 50% anthesis and silking, ear height, and percentage of barrenness, although for all traits measured, significant genotypic variation persisted following 10 cycles of mass selection for adaptation. S1-testcross correlations and percentage midparent heterosis tended to be consistent across selection cycles. Five cycles of mild stratified mass selection increased the adaptation of a temperate sweet corn × tropical maize composite to the temperate zone of the United States while maintaining significant genotypic variation.

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Joseph Aguyoh, Henry G. Taber, and Vince Lawson

Sweet corn (Zea mays L.) growers in the upper midwestern U.S. have used clear plastic mulch to improve early yield and advance crop maturity. Results of this practice have been inconsistent because of early season temperature variability and inadequate information on cultivar adaptation. Our objective was to improve the performance consistency by investigating earliness techniques with the early, sugary-enhancer (se) cultivar Temptation planted at two sites. Treatments were bare soil or clear plastic mulch, rowcovers or none, and direct-seeded or transplanted plants. Transplants were produced in the greenhouse in either 50-cell plastic trays or peat pot strips, 2.3 inches × 4.0 inches deep (6 × 10 cm) and were evaluated according to transplant age and cell size. In the cold springs of 1996 and 1997, the use of clear plastic mulch shortened maturity of sweet corn by 1 and 10 days, respectively, for the silt loam site; but no maturity advantage was observed for the loamy sand site. Clear plastic raised the minimum soil temperature by 3.8 to 4.0 °F (2.1 to 2.2 °C) at both sites. The 2-week-old 50-cell tray transplants matured 6 days earlier than the peat pot strip transplants or direct seeded at both locations in 1997. Marketable yield from the transplants was inconsistent by location and year. Four-week-old transplants did not withstand field stress and performed poorly regardless of type of container. Ear quality as indicated by row number, ear diameter, ear length, and tipfill was lowest with transplants.

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Pedro Revilla, Pablo Velasco, María Isabel Vales, Rosa Ana Malvar, and Amando Ordás

Field corn (Zea mays L. var. mays) cultivar heterosis could improve sweet corn (Zea mays L. var. rugosa Bonaf) heterotic patterns. Two Spanish field corn (Su) and two sweet corn (su) heterotic patterns have been reported previously. The objective of this study was to determine which sweet × field corn crosses could be used to improve sweet corn heterotic groups. A diallel among three sweet corn cultivars (`Country Gentleman', `Golden Bantam', and `Stowell's Evergreen') that are representative of the variability among modern sweet corn cultivars, and three field corn synthetic cultivars [`EPS6(S)C3', `EPS7(S)C3', and `EPS10'] representing the heterotic patterns involving Spanish field corn, was evaluated for 2 years at two locations in northwestern Spain. Differences in heterosis effects (h jj') and average heterosis (h) were significant for all traits except grain moisture. Differences for cultivar heterosis (h j) and specific heterosis (s jj') were significant for grain yield, plant height, and kernel row number. `EPS6(S)C3' had lower s jj' for yield in crosses to `Golden Bantam' than to `Stowell's Evergreen', while `EPS7(S)C3' had higher s jj' in crosses to `Golden Bantam' than to `Stowell's Evergreen'. The best crosses to establish enhanced sweet corn heterotic patterns involving Spanish maize would be `Golden Bantam' × `EPS6(S)C3' and `Stowell's Evergreen' × `EPS7(S)C3'. New sugary 1 cultivars would require preliminary cycles of intrapopulational recurrent selection for agronomic performance and flavor prior initiating an interpopulational recurrent selection program to enhance heterosis.

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Steven D. Siegelin, Darrel D. Daniels, Merrill A. Ross, and Stephen C. Weller

This study was conducted in 1993 and 1994 to determine if nicosulfuron or primisulfuron had any adverse effects on ear or whole-plant development. Factors considered were cultivar, herbicide, rate, and timing of application. Four sweet corn cultivars: `More' (su), `Calico Belle' (se), and `Frontier' and `Challenger' (sh2) were evaluated for foliar injury, plant vigor, plant height (1994 only), ear injury, and yield. Nicosulfuron and primisulfuron were applied at two rates: the labeled rate (x) of 35 g a.i./ha and 40 g a.i./ha, respectively, and at the 2x rate. Herbicides were applied early postemergence at V2 (corn height 10–15 cm) or late postemergence at V7 (corn height 30–50 cm). Plant foliar injury ratings, ear injury ratings, number of ears, number of injured ears, and yields were collected. Ears with injury were described as pinched. There was a constriction of the cob, caused by a reduction in kernel row number, ranging from two to eight rows lost. Sweet corn cultivars varied in their response to nicosulfuron and primisulfuron. Timing of application had a greater impact on ear injury than did the rate. Applications at the V7 stage caused more severe ear injury than application at the V2 stage. Ear injury was more severe in nicosulfuron treatments than primisulfuron treatments. Height reductions were caused by both compounds at both applications, with primisulfuron causing greater stunting. Primisulfuron caused more severe foliar injury.

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T.E. Dickert and W.F. Tracy

Heterosis in corn (Zea mays L.) usually results in earlier flowering, larger plants, and increased yield. In extremely early sweet corn the effect of heterosis on flowering time may be reduced or eliminated due to developmental and physiological requirements for vegetative growth before the transition to reproductive phase. The objective of this study was to determine the level of heterosis and the combining ability for flowering time and other agronomic traits in a diallel cross of six very early open-pollinated sweet corn cultivars. The diallel was grown in 1995 and 1996. Hybrids and parents averaged over hybrids differed for silk date, plant height, ear height, 10-ear weight, ear length, and 100-kernel weight but did not differ for row number and ear width. Heterosis for silk date was significant, but the difference between parents and hybrids was very small, 0.5 day. No hybrids were earlier than the earliest parent, and average midparent heterosis was -0.8%. In contrast midparent heterosis was significant and relatively high for 100-kernel weight (10.0%), ear length (12.9%), ear height (8.6%), plant height (9.0%), and 10-ear weight (28.2%). The traits with low heterosis had very high general combining ability/specific combining ability ratios while these ratios were much smaller in traits with high heterosis. Heterosis for many of the traits, including 10-ear weight, was higher than published values. Conversely, heterosis for flowering time was small, compared to other traits in this study and to published values for silk date, indicating that this extremely early germplasm may be at or near the limit for flowering time under the photoperiod and temperatures typical of summer in Madison, Wis. (43.05°N, 89.31°W).

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Bernardo Ordás, Rosa A. Malvar, Amando Ordás, and Pedro Revilla

showing silks. Plant height, ear length, ear diameter, row number, kernel depth, and kernel width were measured on five plants taken from competitive adult plants in each plot. Yield was measured in each plot and adjusted at a kernel moisture of 140 g