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  • Author or Editor: Martin M. Williams II x
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Sweet corn is planted over a 3-month period in the north central United States to extend availability for fresh market and processing; however, the extent to which development and growth of sweet corn changes during this period is unreported. Field experiments were conducted in 2006 and 2007 to determine the effect of five planting dates, ranging from mid-April to early July, on sweet corn establishment, growth, and yield components. Day length at the time of silking decreased from 15.1 h in the mid-April planting to 13.7 h in the early July planting. Development took 13 to 25 fewer days from emergence to silking for the hybrid ‘BC0805’, an 82-day augmented sugar enhancer endosperm type, as planting was delayed from mid-April to early July. Maximum height generally increased through planting dates with as much as 23% taller plants in early July versus mid-April planted sweet corn. While leaf mass was unaffected by planting date, maximum leaf number and rate of leaf appearance steadily decreased with later planting dates. Lower reproductive and total biomass at silking as well as marketable ear yield components were lowest in the early July planting date and were associated with presence of maize dwarf mosaic virus in leaf samples. In response to environmental conditions, the crop canopy undergoes distinct morphological changes as planting is delayed, and those changes may have implications for crop production.

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Yield stability (simply “stability”) is a crop genotype’s performance over a range of environmental conditions, such that a specific genotype may be less sensitive to environmental change (i.e., above-average stability) or more sensitive to environmental change (i.e., below-average stability) relative to other genotypes. The ideal genotype for most crops is believed to have both above-average yield and above-average stability. The objective of the study was to determine the pattern of genotype adoption and use of processing sweet corn in relation to yield and stability. I hypothesized that if yield and stability influence decision-making on genotype choice, then differences among commercial genotypes in such traits would relate to the pattern of adoption and use of those genotypes. Stability analyses of ear mass and case production were conducted on processing sweet corn genotypes grown in varied environments of the United States’ Upper Midwest and Pacific Northwest. Yield and stability of the 12 most tested genotypes were then related to the extent of their adoption and use by a sweet corn processing company over a 20-year period. Although some genotypes exhibited above-average yield or above-average stability, data revealed there was no evidence of both traits in individual genotypes currently used in processing sweet corn. Adoption of genotypes with below-average yield or stability was less than other genotypes. Genotype adoption pattern of case production showed the greatest proportion of adoption of above-average stability genotypes. Stable case production across all environments is a more important trait in a genotype to the sweet corn processor than a genotype with record yields under favorable conditions. This conclusion is consistent with the industry’s need to have a predictable level of performance in the processing facility, through which all raw product must flow, on a daily basis for the about three-month window of harvest in the northern United States.

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Improvements in plant density tolerance have played an essential role in grain corn yield gains for ≈80 years; however, plant density effects on sweet corn biomass allocation to the ear (the reproductive ‘sink’) is poorly quantified. Moreover, optimal plant densities for modern white-kernel shrunken-2 (sh2) hybrids are unknown. The objectives of the study were to 1) quantify the effect of plant density and hybrid on the reproductive sink of sweet corn and 2) determine optimal plant densities for white-kernel sh2 sweet corn. Field experiments were conducted across 2 years on 10 white-kernel sh2 hybrids grown at plant densities ranging from 4.3 to 8.6 plants/m2. Increasing plant density negatively influenced reproductive sink characteristics of individual sweet corn plants, including linear decreases in ear shoots/plant, marketable ears/plant, ear length, filled ear length, ear mass/plant, and kernel mass/plant. Reproductive traits varied widely among hybrids, including ear mass (15.6–20.6 Mt·ha−1) and recovery (32.3% to 42.4%), which is the contribution of fresh kernel mass to total ear mass. Hybrids had a common response to plant density, whereby ear yield was optimized at 5.5 plants/m2 and gross profit margin was optimized at 6.1 plants/m2. Plant density data from 586 growers’ fields suggest current seeding rates have optimized the reproductive sink size for today’s white-kernel sh2 hybrids. However, room exists for improving plant density tolerance, yield, and profitability.

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Snap beans are cultivars of common bean (Phaseolus vulgaris) that are cultivated for their fleshy immature pods that exhibit a wide diversity of pod shapes and sizes. The genetic basis of the snap bean pod shape is complex and involves the interaction of multiple genes. This study used a snap bean diversity panel composed of heirloom and improved cultivars used in North America and genome-wide association studies (GWAS) to investigate the genetic basis of pod morphological characteristics, including length, width, height, width/height ratio, and coefficients of variation (CVs). The GWAS detected multiple genomic regions associated with each pod trait, with a total of 20 quantitative trait loci (QTLs) for pod length, 9 for pod width, 14 for pod height, and 10 for pod width/height ratio. Regarding the CV of each pod trait, genome-wide association analyses detected six QTL for length CVs, five for width CVs, 15 for height CVs, and six for width/height ratio CVs. Thirteen regions in seven chromosomes were associated with two or more pod traits. Eighteen QTLs for pod traits in this study colocated with previously reported QTLs for pod and seed traits. The QTL intervals encompass gene models with homologues in other species that are involved in the control of developmental processes. These results capture the complex nature of the genetic control of snap bean pod traits and confirm the significance of genomic regions harboring overlapping QTLs identified in this and other studies. The phenotypic expression of pod traits in snap bean appears to be under the control of a few genomic regions with a strong effect with additional contributions of multiple small-effect regions. Validation of the function of the candidate genes identified in associated regions will contribute to our understanding of legume pod development.

Open Access

Consumer demand for edamame [Glycine max (L.) Merr.], the vegetable version of soybean (Glycine max), has grown during the past decade in North America. Domestic production of edamame is on the rise; however, research to guide fundamental crop production practices, including knowledge useful for developing appropriate recommendations for crop seeding rate, is lacking. Field experiments near Urbana, IL, were used to quantify edamame response to plant density and determine the economically optimal plant density (EOPD) of machine-harvested edamame. Crop growth and yield responses to a range of plant densities (24,700 to 395,100 plants/ha) were quantified in four edamame cultivars (AGS 292, BeSweet 292, Gardensoy 42, and Midori Giant) across 2 years. Plots were harvested with the Oxbo BH100, a fresh market bean harvester. In general, as plant density increased, branch number and the ratio of pod mass to vegetative mass decreased, while plant height and leaf area index increased. Recovery, the percent of marketable pods in the machine-harvested sample, varied among cultivars from 86% to 95%. Results identified the EOPD for machine-harvested edamame ranged from 87,000 to 120,000 plants/ha. When considering the effect of plant density on plant morphology, as well as seeding cost, harvester efficiency, recovery, and marketable pod yield, edamame EOPDs are considerably lower than seeding rates of up to 344,200 seeds/ha recommended in recent publications.

Open Access

Poor crop establishment is a major problem in edamame (Glycine max), a specialty type of soybean produced in locations throughout the United States. The objective of this research was to quantify the extent to which seed treatment with fludioxonil + mefenoxam improves seedling emergence of edamame. Emergence characteristics of fludioxonil + mefenoxam-treated and nontreated seed of 30 cultivars were characterized in field conditions over 2 years. Edamame cultivars used in the study exhibited poor field emergence in a previous study despite high germinability. Seed treatment with fludioxonil + mefenoxam at 2.5 and 3.75 g/100 kg seed, respectively, improved crop emergence 33% to 47% more than the nontreated control. The emergence rate (days to 50% emergence) was improved the most by the seed treatment for several cultivars that were generally slow to emerge. Crop establishment is essential for further development of domestic edamame production. Seed treatment with fludioxonil + mefenoxam, at the rate currently registered for use on grain-type soybean, offers one approach to help vegetable growers improve edamame seedling emergence.

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Sweet corn (Zea mays L. var. rugosa or saccharate), consumed both fresh and processed (primarily canned or frozen), is a popular vegetable crop in the United States. Recent nationwide data have reported declining trends in sweet corn production, which poses serious challenges for the US processing sweet corn producers. Here, we evaluated a processing sweet corn dataset that represents nearly 3 decades (1992–2018) of commercial production in the Upper Midwest and the Pacific Northwest regions in an attempt to understand national trends in US processing sweet corn. The objectives of this study were to (a) quantify trends in processing sweet corn production (harvest area and total green ear mass production); (b) understand trends in planting date, plant population density, and hybrid lifespan; and (c) estimate interannual yield deviations in green ear mass yield. Our results reveal declining trends in sweet corn hectares, particularly in rainfed production systems of the Upper Midwest. For the past 3 decades of commercial sweet corn production, plant population density and planting dates used by vegetable processors have remained unchanged. Our analysis revealed a large range (1 to 20 years) in hybrid lifespan, which can be attributed to wide differences in hybrid yield stability across the diverse production environments in the United States. Rainfed production systems are becoming scarcer because sweet corn yields under rainfed conditions are particularly susceptible to severe weather, including heat and drought stress events. Future research is needed to understand sweet corn yields as a function of climatic and nonclimatic variables to stabilize the industry, particularly given predictions of a future with more frequent weather extremes.

Open Access

Edamame growers currently rely heavily on planting depth recommendations for grain-type soybean, despite stark differences in seed characteristics between the two types of cultivars, most notably seed size. Therefore, the objective of the study was to determine the effects of planting depth and seed size on edamame emergence. A popular edamame cultivar used in commercial production was sorted into “small” (23.7 g/100-seed) and “large” (36.8 g/100-seed) seed-size classes, then planted at depths of 1.0, 2.0, 3.0, and 5.0 cm in field experiments. Experiments were conducted in four environments as a split-plot experimental design with four replications. Seed size did not influence total emergence; however, small seed emerged 10% faster than large seed. Although planting depth recommendations for grain-type soybean are 3.2 to 4.5 cm, our results showed edamame emerged more completely and quicker at the shallowest depths examined. The research could be expanded to capture greater diversity in growing environments and crop cultivars; however, the vegetable industry now has research-based information to guide preliminary recommendations regarding appropriate planting depth of edamame.

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Research in dent corn has found significant variation in crop/weed competition for light among hybrids. However, little has been published on the extent of variation in sweet corn competitive ability. Field studies were conducted under weed-free conditions to quantify canopy development and light environment among three sweet corn hybrids and to determine associations among canopy characteristics to crop yield. An early-season hybrid (Spirit) and two midseason hybrids (WHT2801 and GH2547) were grown at experimental sites located near Urbana, Ill., and Prosser, Wash., in 2004 and 2005. Maximum leaf area index (LAI) and intercepted photosynthetically active radiation (PAR) was typically highest for GH2547 and lowest for Spirit. Most differences in vertical LAI among hybrids was observed above 60 and 150 cm in Illinois and Washington, respectively, with WHT2801 and GH2547 having leaf area distributed higher in the canopy than Spirit. Both number and mass of marketable ears were positively correlated with maximum relative growth rate (correlation coefficients 0.60–0.81), leaf area duration (0.68–0.79), total LAI (0.56–0.74) at R1, and intercepted PAR (0.74–0.83) at R1. Differences in canopy properties and interception of solar radiation among Spirit, WHT2801, and GH2547 lead us to hypothesize that variation in weed-suppressive ability exists among hybrids. Future testing of this hypothesis will provide knowledge of interactions specific to sweet corn useful for developing improved weed management systems.

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Knowledge of cultivar-specific information on crop tolerance, the ability of the crop to endure competitive stress from weeds, has garnered recent interest in organic crop production. Twenty-five commercial sweet corn hybrids from nine seed companies were grown in the presence and absence of wild-proso millet (Panicum miliaceum L.) to 1) quantify tolerance in crop growth and yield to weed interference; 2) determine associations between tolerance in crop growth and yield; and 3) identify hybrids differing in tolerance to weed interference. Despite large differences in canopy architecture among hybrids, crop height and leaf uprightness were minimally affected by weed interference. In contrast, wild-proso millet interference reduced ear number 11% to 98% and ear mass 24% to 82% depending on the hybrid. The ability of a hybrid to make small growth adjustments in the presence of wild-proso millet appeared to have no relationship to yield tolerance. The least competitive hybrids were ‘ACX1413’, ‘Optimum’, ‘Quickie’, ‘Spring Treat’, and ‘Sugar Buns’. The most competitive hybrids were ‘Code128’, ‘Coho’, ‘El Toro’, ‘EX 8716622’, and ‘Legacy’. Although some exceptions were observed, in general, the longer-maturity processing hybrids were more competitive with wild-proso millet than the earlier-maturing fresh market hybrids.

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