ii ACKNOWLEDGEMENTS I thank our Lord Jesus Christ for giving me the ability to complete this degree. Your love, faithfulness and guidance have been my instruments for this achievement. I would like to thank my husband, Edwin, and my children, Elaisa and Casiano III, for their love, support and understanding while pursuing this degree. I am also thankful to Raun family, and to my relatives, brothers and sisters in Christ and friends for being supportive and helpful in anyway they can. I am also grateful to the Department of Plant and Soil Sciences for granting me the opportunity t