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Nader Soltani, Peter H. Sikkema, and Darren E. Robinson

Limited information exists on sweet corn (Zea mays) tolerance to postemergence (POST) applications of thifensulfuron-methyl under Ontario growing conditions. Eight sweet corn hybrids were evaluated for tolerance to thifensulfuron-methyl in four field experiments conducted in 2003 and 2004. Thifensulfuron-methyl was applied POST at 6 and 12 g·ha–1 a.i., the registered and twice the registered rate for use in soybean in Ontario. Sweet corn hybrid responses to thifensulfuron-methyl varied. Delmonte 2038 was the most sensitive to thifensulfuron-methyl and had as much as 92% visual injury, 76% height reduction, and 98% yield reduction compared to the nontreated control. Empire, GH1861, GH2298, and GH2684 hybrids showed visual injury of 53%, 55%, 53%, and 61%, height reduction of 34%, 31%, 32%, and 26% and yield reduction of 77%, 68%, 68%, and 51%, respectively. GG214, GH2547, and GSS9299 sweet corn hybrids were not as sensitive to thifensulfuron-methyl. The initial sensitivity observed in these hybrids was minimal and transient with no effect on yield. Although thifensulfuron-methyl is safe for use on some sweet corn hybrids, it has the potential to cause severe crop injury and yield reduction in other hybrids and therefore it should not be recommended for weed management in sweet corn production in Ontario.

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V.M. Russo, J. Williamson, K. Roberts, J.R. Wright, and N. Maness

Sugars move through stalks to be deposited in kernels in sweet corn (Zea mays L.). Concentrations of sugars in stalks change as plants pass through developmental stages. To follow such changes, carbon-13 nuclear magnetic resonance spectroscopy (C-nmr), a technology that can measure concentrations of sugars in tissues, was compared with analysis by high-performance liquid chromatography (HPLC). A shrunken-2 hybrid (cv. Illini Gold), was monitored from mid-whorl to fresh-market maturity (R3). Internodes near the base of the stalk, just below the ear, and between an ear and the tassel were sampled at each developmental stage. Chemical shifts in C-nmr spectra were measured in parts per million hertz (ppm) down-field relative to tetramethyl silane. Through silk emergence (R1) C-nmr spectra were similar regardless of internode, having line positions between 60 and 105 ppm. Unique lines for glucose, fructose, and sucrose were at 96, 98, and 104 ppm, respectively, and mole fractions were similar to those determined by HPLC. The highest concentrations were recorded at R1 for sucrose (26.1 mg·mL-1), from tasseling (VT) through R3 for fructose (avg. 30.4 mg·mL-1), and from VT to R1 for glucose (avg. 32 mg·mL-1). Carbon-13 nuclear magnetic resonance spectroscopy can be used, with minimal sample handling, to monitor sugar concentrations in sweet corn.

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J.R. Heckman, W.T. Hlubik, D.J. Prostak, and J.W. Paterson

Research was conducted with sweet corn (Zea mays L.) to evaluate the presidedress soil NO3 test (PSNT) originally developed for use on field corn on a wide range of New Jersey soils. Soil NO3-N concentrations reflected differences in N availability due to manure or preplant N application. The relationship between soil NO3-N concentration and relative yield of marketable ears was examined using Cate–Nelson analysis to define the PSNT critical level. Soil NO3-N concentrations >25 mg·kg–1 were associated with relative yields at ≥92%. The success rate for the PSNT critical level was 85% for predicting whether sidedress N was needed. Including NH4-N in the soil analysis did not improve the accuracy of the soil test for predicting whether sidedress N was needed. Although the PSNT is quite accurate in identifying N-sufficient sites, it appears to offer only limited guidance in making N-fertilizer rate predictions. The PSNT is most useful on manured soils, which frequently have sufficient N. The test likely will help decrease the practice of applying “insurance” fertilizer N and the ensuing potential for NO3 pollution of the environment.

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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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V.R. Bachireddy, R. Payne Jr, K.L. Chin, and M.S. Kang

The analysis of variance of a data set made up of 30 sweet corn (Zea mays L.) hybrids evaluated over 5 years for marketable ears (dozens per hectare) indicated a significant genotype (hybrid) × year (GY) interaction. Three selection methods were compared: 1) a conventional method based on mean yield alone (YA), 2) Kang's ranksum (KRS) method, and 3) Kang's modified rank-sum (KMR) method. The number of hybrids selected on the basis of YA, KRS, and KMR was 13. The KRS selected the lowest number of unstable hybrids (three) compared with the YA and KMR, which selected eight and six unstable hybrids, respectively. The mean yields of the selected hybrids were 3034 dozen/ha for YA, 2945 dozen/ha for KRS, and 3019 dozen/ha for KMR. The mean yield of KRS-selected hybrids and KMR-selected hybrids was <2.9% and 0.5%, respectively, than that of YA-based selections. This yield reduction was regarded as insignificant considering the farmer would be able to choose more consistently performing hybrids on the basis of KRS than on the basis of KMR or YA. Heterogeneity due to environmental index is the mean of all genotypes in the jth year and X is the overall mean) was significant and was removed from the GY interaction. The removal of heterogeneity revealed that hybrids 77-2269, 116-Kandy Korn-EH, Golden Queen, 141-Sundance, Merit, and Stowell Evergreen were unstable because of a linear effect of the environmental index, and that hybrids 76-2681 and 806F-Truckers showed stable performance due to a linear effect of the environmental index.

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Jian Fang, Frank Moore, Eric Roos, and Christina Walters

Seed moisture content (MC) has been considered the most important factor controlling physiological reactions in seeds, and MC changes with relative humidity (RH) and temperature (T). This relationship is revealed by studying the interaction of RH and T at equilibrium. Cucumber (Cucumis sativus L.), lettuce (Lactuca sativa L.), maize (Zea mays L.), onion (Allium cepa L.), pea (Pisum sativum L.), and watermelon (Citrullus lanatus M. & N.) seeds were equilibrated over sulfuric acid (1% RH) and various saturated salt solutions (5.5% to 93% RH) at temperatures from 5 to 50 °C. Best-fit subset models were selected from the complete third-order model MC = β0 + β1 *RH + β2 *T + β3 *RH2 + β4 *T2 + β5 *RH*T + β6 *RH3 + β7 *T3 + β8 *RH*T2 + β9 *RH2*T, using Mallows' minimum Cp as the selection criterion. All six best subset models (R 2, 0.98 to 0.99) had the same functional form, MC = β0 + β1 *RH + β2 *T + β3 *RH2 + β5 *RH*T + β6 *RH3 + β9 *RH2*T. Coefficients had essentially the same respective values among all species except onion and pea, for which some coefficients were statistically different from those of the other species (P ≤ 0.05). All models indicated that seed MC increased as RH increased and decreased as T increased; but RH had the greater influence. The inverse relationship between seed MC and T, although slight, was evident in the response surfaces. The interaction effect of RH and T on MC was significant at P ≤0.001. These results suggest that orthodox seed species respond similarly to T and RH. This in turn suggests that a common model could be developed and used for optimizing seed storage environments.

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Gunching Siriwitayawan, A. Bruce Downie, and Robert L. Geneve

Sweet corn (Zea mays L.) and tomato (Lycopersicon esculentum Mill.) seeds were aged naturally for 18 months or artificially aged using saturated salt accelerated aging to provide seed lots that differed in seed vigor, but retained a high standard germination percentage. Seed vigor was confirmed using standard vigor tests, including time to radicle emergence, cold, and accelerated aging tests. Ethylene evolution from both sweet corn and tomato seeds during germination was positively correlated with seed quality. Differences in ethylene evolution between nonaged and aged seeds were greater in seeds germinated on exogenous 1-aminocyclopropane-1-carboxylic acid (ACC). After 36 hours, there was about a 15-fold increase in ethylene evolution from seeds treated with 5 mm ACC compared to untreated seeds. Naturally and artificially aged seeds responded similarly and showed reduced ethylene production compared to nonaged seeds. In contrast to ethylene production, endogenous ACC titers were less for nonaged compared to aged seeds. Exogenous application of ACC to artificially aged seeds reduced the time to radicle protrusion, but did not completely reverse age-related effects on vigor. The data indicate that the reduced ability to produce ethylene in aged seeds was related to ACC oxidase (ACCO) synthesis or activity. Using Northern blot analysis, ACCO mRNA was detected after 48 hours of imbibition in nonaged seeds, but was undetectable in aged seeds affirming the contention that ACCO synthesis was delayed or reduced by aging. The current study provides additional support for ethylene as a biochemical indicator of seed vigor in seed lots with reduced vigor but high germination capacity.

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Jose Alvarez and C.A. Sanchez

The economics of producing sweet corn (Zea mays L.) and head lettuce (Lactuca sativa L.) on Florida Histosols were analyzed with and without P application constraints based upon quadratic response functions derived from two experiments with each crop. At the lower end of the historical price range, production of both crops is unprofitable, especially when P is constrained. At higher prices, net returns for sweet corn under P constraints are relatively small compared with the capital invested; net returns are higher for lettuce. However, an analysis of historical monthly prices showed that those high prices rarely occur. Values for the marginal contribution of the last unit of P show that constraints greatly limit net returns. Many sweet corn and head lettuce producers may be forced out of business if P fertilization rates are arbitrarily lowered below the economic optimal rate.

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I.J. Warrington and R.A. Norton

Plants of chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura], radish (Raphanus sativus L.), corn (Zea mays L.), and cucumber (Cucumis sativus L.) were grown under 8-, 12-, 18- or 24-hour daylengths and at three photosynthetic photon fluxes (PPF) within each daylength to evaluate growth and development responses to daily quantum integral (PPF × duration). For the same daily quantum integral, dry matter accumulation and leaf area development were less under 24-hour than under 18-hour daylengths with chrysanthemum and radish. With corn and cucumber, these values were similar under 12-, 18-, and 24-hour daylengths. In all of the species, leaf area and dry matter development were lowest under the 8-hour daylength. Continuous (24-hour) daylength produced some growth abnormalities in radish and chrysanthemum. Specific leaf weight in all species and flower node count in cucumber were linearly related to daily quantum integral up to the highest values examined (73.5 mol·day-1·m-2). All species showed expected photoperiod responses with respect to flowering, but the rate of floral development and number of flower buds formed were highest under the highest PPF (and highest daily quantum integral) treatments. The results indicate that field phenotypes can be obtained in controlled environment (CE) conditions, providing the field daylength and daily quantum integral conditions are reproduced.

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L.W. Lass, R.H. Callihan, and D.O. Everson

Predicting sweet corn (Zea mays var. rugosa Bonaf.) harvest dates based on simple linear regression has failed to provide planting schedules that result in the uniform delivery of raw product to processing plants. Adjusting for the date that the field was at 80% silk in one model improved the forecast accuracy if year, field location, cultivar, soil albedo, herbicide family used, kernel moisture, and planting date were used as independent variables. Among predictive models, forecasting the Julian harvest date had the highest correlation with independent variables (R2 = 0.943) and the lowest coefficient of variation (cv = 1.31%). In a model predicting growing-degree days between planting date and harvest, R2 (coefficient of determination) = 0.85 and cv = 2.79%. In the model predicting sunlight hours between planting and harvest, R2 = 0.88 and cv = 6.41%. Predicting the Julian harvest date using several independent variables was more accurate than other models using a simple linear regression based on growing-degree days when compared to actual harvest time.