Search Results

You are looking at 21 - 26 of 26 items for

  • Author or Editor: John A. Juvik x
Clear All Modify Search

Total nonstructural carbohydrates (TNC) are important for summer recuperation from injury for cool-season turfgrass. The objectives of this study were to determine if trinexapac-ethyl (TE) [4-(cyclopropyl-a-hydroxy-methylene)-3,5-dioxo-cyclohexane-carboxylic acid ethyl ester] affects TNC content and turf quality of a creeping bentgrass at various application frequencies and rates and to investigate any interactions between the effects of TE and traffic treatments on TNC content. Field experiments were conducted in 1995 and 1996 on a mature stand of `Pennlinks' creeping bentgrass grown on a Flanagan silt loam soil maintained at a height of 1.9 cm. Treatments included a single application (0.28 kg·ha-1) or repeat applications at 2 (0.06 kg·ha-1) or 4 (one at 0.28 kg·ha-1 and one at 0.09 kg·ha-1) week intervals during the first 8 weeks of each experiment. Treatments were arranged in a strip-plot design with TE applications as whole plots and traffic treatments as strip plots. Traffic treatments began at 2 weeks and 2 days after initial applications in 1995 and 1996, respectively and continued until the last evaluation date. Traffic treatments consisted of 4 passes of a 102.2 kg smooth roller, 2 days·week-1 in 1995 and 8 passes daily in 1996. A single aqueous extraction method was used for quantification of glucose, fructose, sucrose, and fructan. TNC was the total of all analyzed fractions. Single applications of TE at 0.28 kg·ha-1 significantly reduced turf quality for 4 weeks in both experiments. Sequential applications of TE at 0.06 kg·ha-1 exhibited reduced quality compared to the control at 4 and 8 weeks in 1995 and 2 weeks in 1996. When TE was applied once at 0.28 kg·ha-1, there was a significant reduction in TNC from 4 to 8 weeks after treatment. In 1996 when TE applications were repeated at 2 and 4 week intervals at 0.06 and 0.09 kg·ha-1, a reduction of TNC from week 4 to week 14 was observed. After 14 weeks the TNC content showed incremental increases. There was no interaction effect between traffic treatments and TE applications in the verdure TNC in either year. In 1996, verdure TNC content was 6% to 17% lower in plots receiving traffic from weeks 4 to 18. These results suggest that high rates of TE, either sequential or single applications, might reduce turf quality or carbohydrate content. While this study has not examined if this is detrimental, multiple TE applications at low rates may minimize any TNC reduction while providing effective growth suppression for extended periods.

Free access

Metabolic characteristics of developing sugary-l maize (Zea mays L.) endosperms were investigated. In the later stages of development (>30 days postpollination), sugary-1 kernels maintained higher levels of many enzyme activities and retained more moisture than normal kernels. Higher enzyme activities were attributed to moisture retention and were not associated with any increase in dry weight accumulation. Of enzyme activities measured at 20 days postpollination, that of ADP-glucose pyrophosphorylase was higher in sugary-1 kernels than in normal, whereas total amylase, a-amylase, and pullulanase activities were lower. Experiments testing the effects of zero, one, two, and three doses of the sugary-1 gene in OH43 endosperms indicated that the sugary-1 phenotype was not expressed until three doses of the sugary-1 gene were present. Decreased activities of amylases, but not of pullulanase, were attributed to an interference in detection by phytoglycogen. Increased ADP-glucose pyrophosphorylase activity is attributed to a response by the maize endosperm cells to increased sucrose concentrations.

Free access

Strong evidence exists to suggest that increased consumption of glucosinolates from Brassica vegetables is associated with reduced risk of cancer induction and development. Development of elite germplasm of these vegetables with enhanced levels of glucosinolates will putatively enhance health promotion among the consuming public. To evaluate levels of glucosinolate phenotypic variation in Chinese cabbage tissue and partition the total phenotypic variation into component sources (genotype, environment, and genotype-by-environment interaction), a set of 23 Brassica rapa L. var. pekinensis genotypes were grown in two different environments (field plots and greenhouse ground beds). Gluconasturtiin and glucobrassicin were found to account for ≈80% of total head glucosinolate content. Significant differences were found in glucosinolate concentrations between the lowest and highest genotypes for glucobrassicin (6-fold) and for gluconasturtiin (2.5-fold). Analysis of variance showed that for the three major glucosinolates (gluconasturtiin, glucobrassicin, and progoitrin), the genotypic effects described most of the phenotypic variation (62% averaged over the three compounds). The next most important factor was genotype × environment interaction (29%), whereas variation affiliated with the environment was found to be relatively minor (8%). These results suggest that genetic manipulation and selection can be conducted to increase glucosinolate content and the putative health promotion associated with consumption of Chinese cabbage.

Free access

Gluconasturtiin is a glucosinolate (GS) present in Chinese cabbage and its breakdown product, phenelethyl isothiocyanate (PEITC), inhibits phase I enzyme activation of endogenous carcinogenic compounds and enhances phase II enzyme detoxication, reducing cancer risk and promoting health in humans. This study was conducted to evaluate the interaction between the genotype and the environment to influence GSs in Chinese cabbage. Twenty-five accessions were grown in three environments and tissue quantified for GS levels by HPLC. While gluconasturtiin was observed to be the most abundant GS form, 3-indolylmethyl GS (glucobrassicin) and 1-methoxy-3-indolylmethyl-GS (neoglucobrassicin) were also found. Significant differences were observed among tissues, genotypes and environments in GS concentration and composition. Gluconasturtiin ranged from 0.56 μmol·g-1

DW in leaf tissue of Hau No. 2 to 11.89 μmol·g-1 DW in Chilsung. There were dramatic differences among different tissues of the same genotype with young leaf and root tissues having significantly higher concentrations of gluconasturtiin than other tissues. Gluconasturtiin in Sandong No. 5 ranged from 1.69 μmol·g-1 DW in mature leaves to 18.69 μmol·g-1 DW in root tissue. GS content of the same genotypes in three different environments indicated that plants grown in the greenhouse had higher GS content compared to field grown plants. Results of this study indicate that genotypic variation and the growing environment have substantial effects on GS content in Chinese cabbage. This investigation provides important information for future genetic and molecular studies and has identified Chinese cabbage genotypes that offer superior health benefits to consumers.

Free access

Ten broccoli [Brassica oleracea L. (Botrytis Group)] accessions were grown in several environments to estimate glucosinolate (GS) variability associated with genotype, environment, and genotype × environment interaction and to identify differences in the stability of GSs in broccoli florets. Significant differences in genetic variability were identified for aliphatic GSs but not for indolyl GSs. The percentage of GS variability attributable to genotype for individual aliphatic compounds ranged from 54.2% for glucoraphanin to 71.0% for progoitrin. For total indolyl GSs, the percentage of variability attributable to genotype was only 12%. Both qualitative and quantitative differences in GSs were detected among the genotypes. Ten-fold differences in progoitrin, glucoraphanin, and total aliphatic GS levels were observed between the highest and lowest genotypes. Only two lines, Eu8-1 and VI-158, produced aliphatic GSs other than glucoraphanin in appreciable amounts. Differences in stability of these compounds among the cultivars were also observed between fall and spring plantings. Results suggest that genetic factors necessary for altering the qualitative and quantitative aliphatic GS profiles are present within existing broccoli germplasm, which makes breeding for enhanced cancer chemoprotectant activity feasible.

Free access

This study was conducted to identify the chromosomal location and magnitude of effect of quantitative trait loci (QTL) controlling sweet corn (Zea mays L.) stand establishment and investigate the impact of dry kernel characteristics on seedling emergence under field conditions. Genetic and chemical analysis was performed on two F2:3 populations (one homozygous for su1 and segregating for se1, the other homozygous for sh2 endosperm carbohydrate mutations) derived from crosses between parental inbreds that differed in field emergence and kernel chemical composition. A series of restriction fragment-length polymorphism (RFLP) and phenotypic markers distributed throughout the sweet corn genome were used to construct a genetic linkage map for each population. F2:3 families from the two populations were evaluated for seedling emergence and growth rate at four locations. Mature dry kernels of each family were assayed for kernel chemical and physiological parameters. Composite interval analysis revealed significant QTL associations with emergence and kernel chemical and physiological variables. Improved emergence was positively correlated with lower seed leachate conductivity, greater embryo dry weight, and higher kernel starch content. QTL affecting both field emergence and kernel characteristics were detected in both populations. In the su1 se1 population genomic regions significantly influencing emergence across all four environments were found associated with the se1 gene on chromosome 2 and the RFLP loci php200020 on chromosome 7 and umc160 on chromosome 8. In the sh2 population the RFLP loci umc131 on chromosome 2 and bnl9.08 on chromosome 8 were linked to QTL significantly affecting emergence. Since seedling emergence and kernel sugar content have been shown to be negatively correlated, undesirable effects on sweet corn eating quality associated with each emergence QTL is discussed. Segregating QTL linked to RFLP loci in these populations that exert significant effects on the studied traits are candidates for molecular marker-assisted selection to improve sweet corn seed quality.

Free access