Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Research was conducted to develop methods for improving rice through somaclonal variation using plant tissue culture techniques. Experiments were directed toward developing an efficient culture system by which plants could be efficiently regenerated in rice somaculture. Histological studies of the process of callus formation and plant regeneration were also carried out. Explant sources evaluated for their potential for callus induction and plant regeneration included seedling mesocotyl, root-tips, embryos from mature seeds, nodes, immature panicles, and mature panicles. Immature panicles gave the best callus induction and plant regeneration. It was determined that it was necessary to add 2,4-D to the medium to initiate callus induction. The combination of indoleacetic acid (0.5 mg/l) and benzyladenine (0.8 mg/l) or naphthaleneacetic acid (2 mg/l) and kinetin (1 mg/l) in Murashige-Skoog medium gave the best plant regeneration. It was found that 3% sucrose was optimum for both callus formation and plant regeneration. Callus induction from immature panicle explants was highest after incubation in the dark at 28(DEGREES)C. Plant regeneration was highest with incubation under fluorescent light for 16 hours at 28(DEGREES)C. More effective callus growth and plant regeneration were obtained when small calli (20-40 mg) were transferred to plant regeneration medium. More than 5,000 plants were regenerated from several U.S. and foreign cultivars. Two hundred somaclones from the rice cultivar Labelle and one hundred from the cultivar Lemont were evaluated for variation in morphological and agronomic characters and for yield potential in the field in 1985. An additional 358 lines from Labelle and 218 lines from Lemont were tested in the field for changes in resistance to the rice sheath blight disease. Variation was observed in the following characters: albinism, days to heading, sterility, leaf blade angle, flag leaf angle, culm angle, leaf color, leaf pubescence, leaf senescence, culm strength, resistance to rice sheath blight, panicle type, panicle exsertion, sterility, seedling height at the maximum tillering stage, mature plant height, panicle length, panicle number, panicle weight, 100-seed weight, and yield. Lemont somaclonal line 726 yielded 12% more than the Lemont cultivar.