Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/10/1996
Publication Date: N/A
Citation: Interpretive Summary: A plant variety can be made resistant to a virus disease by the incorporation of certain genes from the virus into the genetic structure of the variety. By this approach, resistance to specific virus diseases may be added to an established cultivar with little or no alteration in the proven agronomic characteristics of the cultivar. However, few plants to which the virus gene is added actually acquire resistance to the virus, an the processes involved in adding a foreign gene to the genetic structure of the plant, called transformation, often changes plant yield and quality characteristics that are agronomically important. Therefore, rigorous selection among hundreds of different transformed plants is usually required to identify transformed lines that are both virus resistant and conform to or exceed standard characteristics of the original, susceptible cultivar. This chapter outlines selection methods that have been successful in the selection process required.
Technical Abstract: Agronomic assessment and selection among plants transformed with viral genes to achieve virus resistance are required because the transformation and tissue culture processes involved frequently alter varietal characteristics that are agronomically important. Two types of changes occur. One is somoclonal variability caused from a restructuring and realignment of the genetic code as new genes are inserted. Such changes are very common and may be subtle among transformed plants. Another type of change is caused by expression of the inserted gene, either an epistatic effect due to effects of the inserted gene on surrounding genes, or the direct expression of the inserted gene. Rigorous selection among hundreds of transformants may be required to identify lines that are both virus resistant and conform to or exceed standard agronomic characteristics of the parent cultivar. Selection for resistance and agronomic performance can proceed concurrently. The principles and general guidelines for selection among plants altered by transformation are the same as those established for classical breeding. The selection procedure is similar to the classical backcross method of introgressing a gene into a commercial cultivar since the objective in both is to alter but one characteristic of the cultivar.