Evaluating the Genetic Diversity of Pyrus Communis Seedlings

The pear (Pyrus Communis) breeding efforts in the US are focused on developing rootstocks with desirable traits such as dwarfing, disease resistance, vigor, precocity, and cold tolerance. One of the challenges encountered towards this goal is finding genetically diverse parent material and genotypes that are adapted to the US environment. We have established a pear seedling population from crosses between ‘Bartlett’, ‘d’Anjou’, and ‘Comice’ genotypes that have survived in the US environment for over a century. Further, we have also established a population where the pollen were exposed to gamma radiation prior to pollination with the aim of enhancing genetic diversity in advanced varieties. This approach has been demonstrated to enhance genetic diversity via the generation of aneuploids. We phenotyped the seedlings and analyzed the genetic relationship among these pear seedlings using Target region amplification polymorphism (TRAP) molecular markers to identify individuals with desirable agronomic traits. TRAP analysis is a cost effective and efficient PCR-based approach used to produce multiple polymorphic markers around targeted gene sequences. TRAP reaction produced a total of 32 polymorphic loci in a population of 185 individuals. The polymorphisms were scored and analyzed using the software programs STRUCTURE, CLUMPP and DISTRUCT, which grouped the pear individuals into sub-populations based on their genetic similarities. From this analysis we identified 14 distinct sub-populations within the main pear population. This information is expected to strengthen the pear breeding efforts in selecting genetically diverse individuals either as parental material or direct candidates for rootstock trials.