Plant Breeders use the principles of genetics to plan and carry out breeding studies to develop and improve varieties of crops. They use their knowledge of plant growth to improve specific characteristics, such as yield, size, quality, maturity, and resistance to frost, drought, disease and insect pests in plants. They develop and select the most desirable plants for crossing by using methods such as inbreeding, crossbreeding, backcrossing, outcrossing, mutating, or interspecific hybridization and selection. Requirements: Written examination required. Any person having a Doctorate Degree in Plant Breeding and three years of experience is not required to take the examination.