Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

First Advisor

Milton C. Rush


The objectives of this research were to study the inheritance of homozygous variation from rice somaculture, to select rice somaclones for increased sheath blight resistance, and to determine the mode of inheritance of the resistance. To accomplish these objectives it was necessary to improve somaculture techniques for rice suspension and protoplast culture especially for the American long-grain cultivars. A method for incorporation of the chemical mutagen, ethyl methane-sulfonate (EMS), into the somaculture system was also developed to increase the frequency of somaclonal variation in tissue culture stable cultivars. The inheritance of six homozygous variant characteristics from five somaclones was investigated. The white apiculus character was controlled by a single recessive gene. Inheritance of the purple apiculus character was controlled by a single dominant gene. Inheritance of the tall variant character from the mutated semi-dwarf cultivar Lemont was controlled by two complementary dominant genes. Inheritance of the short variant characteristic from the cultivar Labelle was controlled by quantitative genes. The genes responsible for the variant characteristics purple-red hulls and dwarfing in Lemont were not stable in the heterozygous F$\sb2$ populations generated by crossing back to Lemont. The "disappearance" of these two characteristics in the segregating generations may be caused by "gene conversion" during meiosis. The possibility that mitotic recombination might be a cause of homozygous somaclonal variation was studied. No mitotic recombination was observed from 1,100 T$\sb1$ plants regenerated from F$\sb1$ progeny from crosses among three genetic marker lines. Two long-grain somaclonal lines resistant to sheath blight were selected from the Labelle cultivar. The resistance of SC86-20001-5 was controlled by a recessive gene. The resistance of SC86-2000l-33 was controlled by two independently inherited recessive genes. A successful suspension culture system was established for both indica and japonic cultivars. By utilizing these suspension systems, an efficient system was developed for plant regeneration from rice protoplasts of the U.S. long-grain cultivar Labelle and the japonica cultivar Taipei 309. By incorporating EMS into callus induction medium at the appropriate concentrations, the inhibitory effect of EMS on plant regeneration was minimized and somaclonal variation frequencies were significantly increased.