Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 80-103). Also available on the World Wide Web.

A rapid non-destructive Image Analysis (IA) technique was developed for the determination of maize kernel endosperm vitreousness. Kernels were analysed using a Leica Q-Win Q500 IW-DX Image Analyser fitted with Leica Q-Win software and connected to a Sony XC-75 CCD camera. Kernel translucency measurements were optimised by using a light system that involved positioning whole kernels on top of a mask containing round illuminated areas (circles), smaller than the projected areas of the kernels, allowing light to shine through the kernels only. Correction factors allowing for constant illumination of kernels were developed to adjust for kernel size variation in relation to constant light area. Similarly, a correction factor for the effect of kernel thickness on detected translucency values were developed. Significant correlations were found between corrected translucency values and vitreous and opaque endosperm yields as determined by hand dissection. These were: translucency as a percentage of the whole kernel and vitreous endosperm (mass%) (Translucency 1), r = 0.77, p<0.00001, and Translucency 1 and opaque endosperm (mass%), r = -0.72, p<0.00001 for white maize. Similar correlations were found for translucency as a percentage of endosperm (Translucency 2). Correlation coefficients increased significantly after kernel thickness corrections. Significant negative correlations were also found between corrected translucency values and Floating Number. For yellow maize, Translucency 1 correlation coefficients was r = 0.78, p<0.00001 and r = -0.71, p<0.00001 respectively with similar correlations for Translucency 2. Correlations were obtained after applying both correction factors for exposure and thickness. The IA technique was evaluated for predicting the yield of vitreous endosperm products during dry maiz~ milling in laboratory and industrial-scale milling trials. Significant positive correlations were found between corrected translucency values and yields of milling products from vitreous endosperm. Experiments using a laboratory-scale experimental roller milling test without a degerming stage produced the following correlations: between Translucency 1 and semolina yield (mass%), 0.74, p<0.001 and Translucency 2 and semolina yield (mass%), 0.70, p<0.001. For industrial-scale milling, a Bühler industrial-scale maize mill (3 tons per hour) was used. The correlation between Translucency 1 and extraction at degermer (degermer overtail yield) was 0.93, p<0.0001. There was a similar correlation for Translucency 2. Yellow maize was degermed using a pilot-scale Beall-type degermer and the correlation between Translucency 1 and flaking grits> 3.9 mm was 0.67, p< 0.001. The IA technique permits the non-destructive analysis of maize endosperm translucency on large samples of single kernels. It is suitable for rapid quantification of maize endosperm contents and predicting dry maize milling performance, as kernel translucency was significantly correlated with vitreousness in all instances. With further development of specific hardware and software, the technique has potential as an on¬line maize kernel classification system in industrial mills. As the method is non¬destructive, it is also suitable for classification of maize seed breeding material. It is also a potential method for the measurement of maize opacity as used by the wet milling industry, where opacity (the opposite of vitreousness) is related to maize starch yield. / Thesis (PhD(Food Science))--University of Pretoria, 2006. / Food Science / unrestricted

Recent reports of damage to maize seedlings where atrazine or atrazine/terbuthylazine was applied post-emergence again raised the issue of maize tolerance to triazines. The potential of atrazine or atrazine/terbuthylazine to injure maize when applied post¬emergence was investigated under controlled conditions. Factors considered were growth stage, surfactants, cultivar tolerance, temperature and crop recovery from herbicide injury. The first experiment was conducted to determine the effect of atrazine and terbuthylazine on maize seedlings, and the second one was carried out to identify whether stage of maize development has an influence on atrazine or terbuthylazine phytotoxicity. In Experiment 1, herbicide treatments were applied at the 2-leaf stage of cultivar PAN 6043, and in Experiment 2 at the 2-leaf and 4-leaf stages. The third experiment was carried out to determine cultivar tolerance to atrazine or atrazine/terbuthylazine. The three cultivars used were CG 4526, PAN 6043 and PAN 6140. The fourth and fifth experiments were carried out in growth chambers where the role of temperature and cultivars were investigated. The temperature levels were 20/15 and 30/25°C (day/night). Herbicide and temperature treatments were applied at the 2-leaf stage of cultivars CG 4526, CAN 3891, PAN 6043 and PAN 6140. Finally, an experiment was conducted to investigate the recovery of maize seedlings from the initial atrazine/terbuthylazine phytotoxicity. The cultivar PAN 6043 was used and the herbicide rates were the recommended and double the recommended rate. The rates of the herbicides and associated activity enhancers were 2.5 L ha-1and 1 L ha-1 respectively. The following products were used: Atrazine 500 SC (485 g L-1 atrazine) + BP Agripon (940 g L-1 mineral oil); Gesaprim Super 600 SC (291 g L-1 atrazine and 291 g L-1 terbuthylazine) + AG Penetrex (363 g L-1); Gesaprim Super 600 SC (291 g L-1 atrazine and 291 g L-1 terbuthylazine) + Complement (363 g L-1). Maize seedlings were tolerant when atrazine or atrazine/terbuthylazine was applied at the 4-leaf stage, but significant damage was caused when application was done at the 2-leaf stage. No significant differences were found between surfactants. Significant differences occurred with cultivars at specific temperatures. At the low temperature regime (20/15°C), CG 4526 showed shoot dry mass (SDM) reduction of > 40 %, while the growth of PAN 6140 was reduced by less than 10 % by both herbicides. However, with an increase in temperature, CG 4526 was the most tolerant. It showed <17 % reduction in SDM while others showed >30 % reduction. It is suggested that the tolerance of maize (specifically at the two-leaf stage) to atrazine or atrazine/terbuthy1azine is dependent on cultivar and temperature. Although initial phytotoxic symptoms were visible several weeks after spraying, the growth inhibition of the atrazine/terbuthylazine-treated maize plants was transient. At five weeks after application, leaf area index (LAI) had recovered 100% and 95% at the recommended and double the recommended rate, respectively. Recovery in SDM and root dry mass (RDM) were similar, with 100% recovery reached after eight weeks following application. It was found that although growth stage plays an important role in the tolerance of maize seedlings when atrazine or atrazine/terbuthylazine is applied post-emergence, surfactants, cultivars, and temperature also have an influence on the tolerance of maize seedlings towards these herbicides. / Dissertation (M Inst Agrar (Weed Science))--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

The introduction of pyramided Bacillus thuringinesiss (Bt) in field corn, Zea mays L. has helped reduce kernel and foliar damage from caterpillar pests including fall armyworm, Spodoptera frugiperda (J.E. Smith) and corn earworm, Helicoverpa zea (Boddie). These pests can also be controlled with diamide insecticides. No compensation for manual kernel damage occurred at any section of the ear for Bt or Non-Bt corn. No consistent impacts on corn growth or yield were observed following foliar applications of diamide insecticides at various growth stages. The diamides exhibit longer residual efficacy than other insecticides available for fall armyworm management in field corn. Based on the level of mortality observed on young tissue developed after treatment with chlorantraniliprole, chlorantraniliprole translocated in corn and could therefore be more beneficial than other insecticides when applied during vegetative growth stages.

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