Micropropagation, genetic engineering, and molecular biology of Populus

Poplar improvement efforts are directed at improving tree traits such as rapid early growth, yield, and fiber quality. The goal of improvement programs is to increase resistance to diseases that have the potential to reduce yields or kill trees. Selection, breeding, and testing for poplar disease resistance are hampered by the long generation time of trees, the difficulty in identifying and capturing desired traits using classical breeding techniques, and the limited knowledge of juvenile-mature correlations of desired traits. Screening for disease resistance in the field is time-consuming, costly, and dependent upon natural fluctuations in inoculum abundance and weather factors that influence pathogen spread, infection, disease development, and disease expression. Trees in field tests are also subject to many pathogens and insect pests that periodically confound test results (Ostry et al. 1989). Various cultural and chemical control strategies have been suggested for most of the major poplar pathogens. If available, the use of resistant clones is the best longterm management practice. Selection of adapted, highly productive clones with disease resistance is not easily achieved. Host-parasite interactions are complex, dynamic, and affected by many environmental variables and the developmental stage and general health of the host. These factors can significantly affect disease resistance or tolerance. Application of new techniques in molecular biology and plant biotechnology to poplar improvement may decrease the time necessary to introduce new traits and increase