Sh2 Sweet Corn Research Articles

Free Fatty Acids in Shrunken‐2 Sweet Corn Seed

High free fatty acid (FFA) levels have been reported in commercial shrunken‐2 (sh2) sweet corn (Zea mays L.) seeds. Objectives of this study included comparison of FFA content of sh2 corn seed with other genotypes and preliminary study of the source of the FFA. Kernel infection by seed‐borne fungi was not consistently correlated with FFA. With toluene extraction, sh2 sweet corn seed averaged 83.2 mmol kg−1 FFA compared with 2.1 mmol kg−1 from dent and 4.8 mmol kg−1 from sugary corn. Hot, water‐saturated butanol for 5 h (HWSB) extracted 57% more FFA from sh2 seed than did toluene. However, HWSB extracted 781% more FFA from dent corn seed than did toluene. Considering the four‐fold greater lipid content of sh2 kernels on a weight basis, this suggests that slightly more than half of the high FFA content of sh2 corn seed observed with toluene extraction resulted from relative lack of starch‐bound lipid in the sh2 endosperm.

FIELD EMERGENCE OF SHRUNKEN-2 CORN PREDICTED BY SINGLE AND MULTIPLE VIGOR LABORATORY TESTS

A rapid and reliable predictor of sweet corn seed field emergence is required to produce high-quality, uniform crops. Field emergence of seven sh2 sweet corn cultivars grown at 3 geographic locations in Florida over 2 planting periods (fall and spring) was correlated with laboratory vigor tests. Factor analysis was used to separate non-collinear vigor tests for subsequent multiple regression models. The best single predictor test (R2=0.93***) was an index based on conductivity of the leachate and germination percentage after complex stressing vigor test incubated at 15°C. Leakage conductivity after 3 h soaking at 25 or 30°C (R2=0.90***), cold test in soil (R2=0.90***), mean alternate temperature stress conductivity test (R2=0.88***), standard germination test incubated at 30°C (R2=0.88***), and the index incubated at 25°C (R2=0.88***) were also good predictors of field emergence. Non-collinear tests including the towel germination test at 25°C and an alternate temperature stress conductivity test generated the highest most significant two factor predictor (R2=0.89***), and with glutamic acid decarboxylase activity (GADA) the best three factor predictor (r2=0.93***). The index of conductivity and complex stressing vigor test (ICS) proposed as a predictor of seed emergence considered two main factors affecting emergence in sh2 sweet corn: the condition of the membrane of the seeds and potential pathogen infection.

BIOLOGICAL SEED TREATMENTS USING TRICHODERMA HARZIANUM FOR HORTICULTURAL CROPS

Biological seed treatments provides an alternative to chemical seed treatments or may also be used in combination with chemicals for effective control of plant pathogens. Seed treatment technologies are an important component of pest management, especially for effective biological control. Several seed treatments have been developed and evaluated to increase efficacy of the bioprotectant, Trichoderma harzianum, including 1) suspending the bioprotectant in a binder for a slurry application, 2) use of film coating technology, termed liquid coating, 3) combination of physiological treatments such as priming with the biological and 4) a dry planter box formulation. A laboratory bioassay consisting of sowing cucumber seeds in Pythium or other pathogen infested soil has shown that seed treatment technologies can enhance the efficacy of the bioprotectant. Field research has been conducted over four growing seasons on standard sugary and sh2 sweet corn. In general, emergence from seeds treated with Trichoderma by the described methods was comparable to seeds treated with chemical pesticides. Furthermore, plant growth was enhanced in several field studies.

SEED TREATMENT EFFECTS ON VOLATILE ALDEHYDE PRODUCTION IN GERMINATING sh2 SWEET CORN.

Seeds of two shrunken-2 (sh2) sweet corn (Zea mays L.) cultivars, `Crisp'n Sweet 710' and `Camelot', were used to relate volatile production to seed quality and seedling establishment. The five seed treatments evaluated were a hydration and drying cycle, a biological control of Pythium, a hydration and drying cycle followed by a biological control, a fungicide treatment, and an untreated check. For the aldehyde assays, 50 seeds were germinated in a flask for 24 h with a test tube of a 3-methyl-2-benzo-thiazolinone hydrazone (MBTH) solution. One ml of the solution was then reacted with FeCl3, diluted with acetone, and absorbance read at 635 nm. A field study was run under cool soil conditions (10-16°C) for seedling emergence and growth. Aldehyde production from the seeds did not correlate with field results for seed treatments, but did show a distinct difference between cultivars. The biological control with the hydration and drying cycle significantly reduced aldehyde production. This may contribute to the effectiveness of biological treatments since Pythium spores can be stimulated by volatile compounds released from germinating seeds.

EFFECT OF NITROGEN AND SULFUR FERTILIZATION ON THE CHEMICAL COMPONENTS OF FLAVOR IN SHRUNKEN-2 SWEET CORN

Dimethyl sulfide (DMS), the compound responsible for the characteristic “corny” aroma, and sugar are the principle chemical components of flavor in sweet corn. It was our contention that it may be possible to enhance the flavor potential of some high-sugar sweet corn hybrids by supplying increased amounts of N and S fertilizer to the crop to increase kernel DMS and sugar content. A factorial combination of two N (168, 310 kg/ha) and three S rates (0, 34, 101 kg/ha) was applied to six sh-2 sweet corn hybrids in a Plainfield sand. Kernel DMS and sugar levels were assayed over a period ranging from 20 to 29 days after pollination. In each case, kernel DMS and sugars decreased with increasing harvest maturity. In three hybrids, there was a positive response in kernel DMS to either N or both N-S. Kernel fructose and glucose concentrations tended to decrease as N fertilization rate increased, while sucrose levels remained relatively constant. In all hybrids, S fertilization had no effect on kernel sugars. The results indicated that it may be possible to increase kernel DMS potential in some genotypes by increased N fertilization, and to a lesser degree, from S application.

Prediction of Sweet Corn Phenology in Subtropical Environments

AbstractLimited information on phenology of sweet corn (Zea mays L.) grown in subtropical regions is available to processors wishing to manage harvest scheduling. This study was conducted to investigate developmental characteristics of both standard sugary (su) and mutant endosperm sugary enhancer (se), and shrunken‐2 (sh2) sweet corn in subtropical Australia. Field experiments were conducted at three locations with numerous times of planting so that a broad range of environments were encountered. Models of daily rate of development for the period sowing to kernel maturity (720 g kg−1 moisture) were derived by an iterative optimization procedure. Development rate was related to mean daily temperature and photoperoid. Temperature was the most important factor affecting rate of development. The temperature response was best described by a broken linear function. Various photoperiod functions fitted as multipliers to the temperature response did not improve goodness‐of‐fit. Cultivars were classified into three maturity groups based on analysis of covariance. Developmental characteristics appeared independent of genetic background as the response of the three sh2 cultivars was not significantly different from a tropical su type, and the se cultivar ‘Sweet Champion’ did not differ significantly from the majority of su types. Only su cultivar ‘Terrific’ differed significantly from both of these groups. Base temperatures (range from 5.4–6.4°C) were lower than the value traditionally quoted for sweet corn (10°C). Optimum rates of development occurred at temperatures ranging from 30.8 to 33.8° C. The models accurately predict the duration of sowing to maturity and were shown to be a practical tool for harvest date prediction of both standard and mutant endosperm sweet corn in subtropical environments.

Reduction of Aphid Contamination on Sweet Corn Ears, 1992

Abstract ‘Dazzel’ (sh2) sweet corn was planted 20 Jun in Tioga silt-loam soil at New Paltz, NY. Treatments were arranged in 2-row plots 149 m long, replicated 4 times in a randomized block design. Foliar spray treatments were applied to silking corn (27 Aug, 31 Aug and 4 Sep) using a high clearance sprayer driven at 2.12 km/hr equipped with three D2-25 cone nozzles/row, dispensing 450 liters/ha at 7.03 kg/cm2. On 9 Sep, 25 ears/replicate were randomly selected and given a rating based on the presence and location of aphid colonies (i.e. > 5 nymphs), where: 0 aphids = 0, aphids at the base of ear = 1, aphids at the side of ear or between husk layers = 2, aphids at the silk zone or on kernels = 3). The numerical ratings were additive if aphids were present at more than one location on the ear. The proportion of ears having a rating of 2 or less was used to determine percent marketability. The presence of aphids at the base is not in itself detrimental to marketability, but aphids located between the layers of husks or within the silks or kernels is cause for rejection.

Respiration and Carbohydrate Metabolism during Germination of sh2 and Sh2 Sweet Corn Seed

Sweet corn (Zea mays var. rugosa L.) seed with the endosperm mutant shrunken-2 (sh2) often exhibit low seed vigor and poor field emergence. Seed respiration and carbohydrate metabolism during germination of supersweet `Jubilee' (sh2) and sugary sweet `Jubilee' (Sh2) were studied. There were no significant vigor differences expressed by isolated embryos from sh2 and sugary (Sh2) seeds, indicating similar embryo physiology. Respiration rates were higher in the sh2 genotype during early stages of germination (24 hours) while they declined later. The available sucrose originating from the endosperm reserves was depleted by day 4. This insufficiency of a sustained energy source due to rapid consumption and minimal stored reserves may limit subsequent seedling growth in the sh2 genotype.

INFLUENCE OF DRY-BACK TEMPERATURES AFTER SOLID MATRIX PRIMING ON SUBSEQUENT SEED PERFORMANCE

The effects of the dry-back temperature on sh2 sweet corn seeds primed via solid matrix priming combined with sodium hypochlorite (SMPsh) were studied. Seeds of two sh2 sweet corn cultivars: Crisp N'Sweet 711 (CNS-711) and How Sweet It Is (HSII) were primed via SMPsh. After the treatment, the seeds were dried-back from 50-54% to 6-7% moisture content at 20, 30 or 40C and 25% RH. The rate of dehydration was significantly lower in CNS-711 compared to HSII at all dry-back temperatures. In both cultivars, seed respiration after 4, 16, and 32h of imbibition was greater in those dried at 30 and 40C compared to 20C or non-primed seed. Enzyme activity (glutamic acid decarboxylase activity) was decreased in HSII seeds dried at 20C. There were no differences among treatments in CNS-711. Leakage conductivity was significantly less when the seeds were dried-back at 30C or 40C compared to 20C or nonprimed seeds. Laboratory germination and seedling fresh weight were greater in seeds dried-back at 30C compared the others temperatures or non-primed seeds. The low rate of desiccation at 20C (30h and 8h in CNS-711 and HSII, respectively) may not suppress germination events after priming, thus damaging the embryo during dry-back. This work demonstrated the importance of dry-back temperature to the efficacy of SMPsh seed treatment in sh2 corn.

Infusion of shrunken-2 Sweet Corn Seed with Organic Solvents: Effects on Germination and Vigor

Sweet corn (Zea mays L. var. rugosa Bonaf.) seed carrying the mutant endosperm gene shrunken-2 (sh2) are very susceptible to seed rot and pre- and post-emergence damping off. Experiments were conducted to determine if selected organic solvents were suitable carriers for fungicide infusion of sh2 sweet corn seed for improved germination and stand establishment. Seed of `Florida Staysweet' and `Crisp-n-Sweet 710' were immersed in acetone, cyclohexane, decahydronaphthalene (Decalin), dimethylsulfoxide (DMSO), ethanol, or xylene for 5 seconds, 0.25, 0.50, 1.0, 2.0, 4.0, or 8.0 hours, air-dried, and subjected to a cold-stress test. Total germination and percentage of normal seedlings in both cultivars were significantly decreased after 8 hours of immersion in acetone. Average seedling dry weight, however, did not decrease. DMSO was highly toxic to both cultivars. Ethanol increased seed mortality with increasing immersion times. Cyclohexane, Decalin, and xylene caused erratic responses in all measured variables as immersion time increased. In a second experiment, the effects of immersion time up to 4 hours in acetone on germination and vigor of 11 sh2 cultivars were compared. There was no correlation between cultivar germination or vigor and immersion in acetone. Results indicate acetone could be used to infuse fungicides into the seed of some sh2 cultivars without compromising seed germination or vigor. However, each sh2 cultivar must be screened individually to determine if it is a suitable candidate for organic solvent infusion of fungicides.

Seed Moisture and Transplant Management Techniques Influence Sweet Corn Stand Establishment, Growth, Development, and Yield

A series of experiments exploring the effect of seed moisture and transplant management techniques was conducted with sh2 and su sweet corn (Zea mays L.). The use of seed and transplants in a progression of developmental stages from dry seed to moistened seed to 14-day-old transplants showed that moistened seed had no impact on plant `growth and development. Use of transplants generally had little impact beyond decreasing percent survival and plant height. Increasing the age of transplants reduced the time to maturity and harvest. Increasing the size of the transplant container (paper pot) decreased the time to harvest for younger seedings, but had no other effects. Premoistened seed were successfully held at 10C for up to 72 hours without damage following moisturization. Delays in irrigation of up to 2 days after planting moistened seed had no detrimental effects on sweet corn emergence and growth.

FIELD PERFORMANCE OF BIO-PRIMING FOR PROTECTION OF sh2 SWEET CORN FROM PREEMERGENCE DAMPING-OFF CAUSED BY PYTHIUM ULTIMUM.

Shrunken-2 supersweet (sh2) sweet corn is susceptible to preemergence damping-off caused by Pythium ultimum, especially when planted into cold soil. Bio-priming, a seed treatment which combines the establishment of a bioprotectant on the seed with preplant seed hydration, was developed to protect seeds from damping-off.In a series of field experiments conducted in Montana's Bitterroot and Gallatin Valleys, bio-priming or seed bacterization with Pseudomonas fluorescens AB254 protected sweet corn from P. ultimum damping-off. Bio-priming corn seed with P. fluorescens AB254 was comparable to treatment with the fungicide metalaxyl in increasing seedling emergence. Seedlings from bio-primed seeds emerged from the soil more rapidly than from nontreated seeds and were larger at three weeks postplanting. Seeds of sh 2 and sugary enhancer (se) sweet corn, as well as that of several sh 2 cultivars, were protected from damping-off by bio-priming.

IMBIBITION, ELECTROLYTE LEAKAGE, AND GERMINATION OF SWEET CORN HYBRIDS CARRYING sh2 MUTANT ENDOSPERM

Seeds of two shrunken-2 (sh2) sweet corn (Zea mays L.) cultivars, Crisp N' Sweet 711 and How Sweet It Is were used to analyze seed quality factor differences between the cultivars. Negative correlations occurred among germination percentage and imbibition, electric conductivity, potassium concentration and total soluble sugars of the seed leachate. Imbibition and total soluble sugar in the leachate significantly increased as imbibition temperature increased from 5°C to 25°C in both cultivars. A significant increase in conductivity of the leachate also occurred in `Crisp N' Sweet 711' when temperature increased. Cracks in the seed coat were more frequent in `How Sweet It Is' than `Crisp N' Sweet 711'. The higher concentrations of soluble sugars in the seed, greater imbibition rate, leakage conductivity, potassium and sugar concentration in the leachate may have been directly related to the poorer seed quality of `How Sweet It Is'. The alteration in cell membrane structure caused by a rapid water uptake in `How Sweet It Is' may have led to the high concentration of electrolytes in the seed leachate. This, in turn, might provide a greater nutritive subtrate for fungi development.

Priming Sweet Corn Seed to Improve Emergence Under Cool Conditions

from primed seed was significantly different than emergence from unprimed seed on each day but 16 and 21 (P = 0.01, arcsin transformation). Corn inbreds planted when soil is 10C and lower are often injured by cold water imbibitional stress (Cohn and Obendorf, 1978). Bodsworth and Bewley (1981) found that polyethylene glycol (PEG) 6000 promoted seed germination of two field corn cultivars when germinated at 10C. The objective of the current study was to evaluate PEG 8000 for improving emergence of two sh2 sweet corn hybrids. Six seeds of sweet corn sh2 hybrids (’Crisp ‘N Sweet’ and ‘How Sweet It Is’; Crookham Seed Co.) were placed in 9-cm-diameter petri dishes containing 15 ml of PEG 8000 absorbed into two sheets of Whatman #1 filter paper. Seeds were in excellent contact with a thin layer of PEG on the surface of saturated filter paper. Concentrations used were 100,200, and 300 g PEG/liter distilled water (-0.16, -0.56, -1.14 mPa, respectively) (Michel, 1983). Seeds were primed at 15C for either 4, 3, 2, or 1 days, such that priming was completed for all seeds on the same day. Control seeds received no treatment. Excess PEG was rinsed off with distilled water. Control and treated seeds were planted immediately after completion of the 4-day priming treatment. Six seeds of each cultivar were placed on the surface of unsterilized potting mixture of 1 vermiculite :1 sand :1 pedite :1 silt loam soil (by volume) in 0.8liter round pots and covered to a depth of 2.5 cm. There were two pots per treatment for each cultivar. Pots were covered with plastic wrap to prevent moisture loss and placed in a growth chamber at 10C for 12

Bio-priming Seed Treatment for Biological Control of Pythium ultimum Preemergence Damping-off in sh2 Sweet Corn

(...) During bio-priming, bacterial populations increased form 10 to over 10,000-fold, depending on initial inoculum level. Bio-priming provided protection against damping-off as good as or better than seed treatment with metalaxyl when the seeds were planted in cold soil. this process may be of interest and value to growers who wish to plant sweet corn or other temperature-sensitive crops into cold soils where damping-off is a problem and the use of chemical seed treatments is not desired

Pericarp Thickness of a Shrunken‐2 Population of Maize Selected for Improved Field Emergence

While the pericarp of maize (Zea mays L.) protects the kernel from pathogenas, thin pericarp is desirable in imparting tenderness in sweet corn. The objective of this study was to determine the correlated response in pericarp thickness due to selection for improved field emergence and seed weight in a shrunken‐2 (sh2) population. Two experiments were performed on a population to determine this relationship. In the first experiment, pericarp thickness of 11 cycles of a sh2 population mass selected for improved field emergence and increased seed weight was examined. Thickness of excised pericarps from mature kernels was measured with a pressure micrometer. Field emergence was determined in replicated trials in Urbana, IL in 1986 and 1987. Although significant differences in pericarp thickness were found, they were not correlated with field emergence. Little of the variation in pericarp thickness was due to linear trends resulting from indirect selection (r2 = 0.15). In the second experiment the pericarp thickness was examined on kernels from 100 ears from each of Cycles 2, 5, 8, and 11 of the same sh2 population. The differences in pericarp thickness among cycles, although significant, were small and did not reflect linear trends related to cycles of selection (r2 = 0.10). Selection for improved field emergence and seed weight in this sh2 maize population did not alter pericarp thickness. Thus, field emergence of sh2 sweet corn maybe improved without increasing pericarp thickness and decreasing tenderness.

Electrolyte Leakage and Seed Quality in a Shrunken-2 Maize Selected for Improved Field Emergence

Abstract Acceptance of shrunken-2 (sh2) sweet corn (Zea mays L.) hybrids is limited by poor seed quality and seedling emergence, especially in cold soils. The conductivity of the electrolytes leached from imbibing seeds, a rapid measurement of seed quality, is highly correlated with field emergence among sweet corn hybrids. Our objective was to determine if conductivity is related to field emergence in a sh2 population that had undergone selection for improved field emergence for 10 cycles. The response of conductivity to indirect selection was linear, and the linear trend accounted for a large portion of the variation in conductivity (r2 = 0.70). Conductivity ranged from 82.0 dS·m–1 in cycle 0 to 35.3 dS·m–1 in cycle 8, with cycle 10 not differing from cycle 8. High conductivity indicates greater electrolyte leakage. At P ≤ 0.01, conductivity was negatively correlated with all seed performance ratings; field emergence (r = –0.82), plant height (r = –0.81), uniformity (r = –0.92), and relative emergence (r = –0.85).

Effect of Compensated-rate Seeding and Seed Protectants on Yield and Quality of a Shrunken-2 Sweet Corn Hybrid

Abstract Seeds of ‘Florida-Sweet’, a high-quality, fresh market, sh2 sweet corn (Zea mays L.), tend to have low germination and the seedlings are also more susceptible to root rot than standard sweet corn (su). Difolatan plus benomyl as seed protectants controlled the soil fungus complex and significantly improved yields without reducing ear quality. Compensated-rate seeding, or seeding adjusted according to germination percentage to give 54,000 plants/ha with seeds of 70% to 100% germination, produced no yield or quality reduction in most cases. However, regression analysis showed in 1 out of 3 tests a significant linear decrease between seed germination percentages and yields of U.S. Fancy ears.