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Doctor of Philosophy




Field experiments were conducted during the growing seasons of 1978 and 1979. In 1978 the effects of hormones IAA and ABA at a concentration range of 10('-5) to 10('-2) M were studied on dry weight (DW) and percent of filled kernels (PFK) of the first ear when hormones were injected about 2 weeks before anthesis into the 14th stem internode (first ear node) of 'Pioneer 3780', a single cross corn cultivar. In another set of treatments, growth regulators IAA, and BA and GA were injected into the 12th stem internode of the same cultivar at a concentration range of 10('-5) to 10('-2) M. Dry weight and PFK of the first ear, DW of the second and third ears and EL and CL of the second and third ears were the attributes measured. Additional studies were conducted to determine the influence of liquid chemical growth regulators ACA (zinc acetate) and ACE (ammonium acetate) on vegetative growth and yield components of 'Pioneer 3780' in three fields collectively called A, B and C;In fields A and B, ACA and ACE were mixed with fertilizer and applied as a band placement when the corn seedlings were at 5th leaf stage. In Field C both ACA and ACE were premixed with NH(,3) and injected into the soil before planting time. Two different methods of application were used in Field C: (a) a close to the row (10 cm) application and (b) a far from the row (40 cm) application;Results on the effect of hormones on PFK and DW of the first ear showed no significant differences between treated plants and controls regardless of the method of application and placement of compounds. This lack of response might be related to the fact that immature grain of corn has been shown to be a source with high concentration of plant growth substances, therefore, it seems unlikely that exogenously applied hormones could have affected the processes of ear growth and development;Despite the significant effect of BA, GA and the low concentration of IAA or NAA in increasing the growth of the second ear, the basipetal pattern of ear shoot development was evident by the decrease in ear size from the top ear downward;The effect of growth regulator compounds on the third ear was similar to that on the second ear, and although they stimulated development of the third ear, they were not able to transfer the third ear from a nonfunctional form to a functional form;In field A a significant increase in leaf width and weight per ear was noticed due to ACA compared to ACE. The results in Field B showed an increase in height of plants and weight per ear with ACA treated plants. The increase in weight per ear due to ACA was to the extent that it caused a significant increase in grain yield;In Field C, ACA and ACE increased leaf width, leaf length, plant height, weight per ear, and grain yield at an an optimum combination of rate of chemical and method of application. At super optimum rates significant adverse effects were noted.



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Gholamreza Khosravi



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167 pages