Evaluation of Simple Sequence Repeats (SSR) for Genetic Analysis of Chestnut Trees in Michigan Orchards

In Michigan, non-grafted seedlings of Chinese descent commonly planted by growers predominate chestnut orchards because of the resistance to chestnut blight. In addition, grafted hybrids of European, Chinese, and Japanese descent, many with unknown pedigrees, are also present in orchards. The outcome of this genetic mixing in orchards is a chestnut product with variable size and quality. Therefore, the objective of this study is to evaluate the use of simple sequence repeats (SSRs) to genetically characterize promising chestnut trees and cultivars currently growing in Michigan orchards. In the summer of 2007, we began a series of crosses in four isolated orchards, where each orchard consisted of two cultivars. Trees of the C. sativa x C. crenata hybrid cultivar 'Colossal' were selected as the female parent for every cross due to its good yield and because it is planted in orchards throughout the state. The chestnut cultivars 'Benton Harbor' and 'Eaton', both with Asian backgrounds, and the European hybrid cultivars 'Nevada', and 'Okei' were selected as pollinizer trees. Fifty nuts per cross were randomly selected as the individuals representing the four populations. We were able to generate fingerprints using both universal and specific primers such as (GTG)(5) and CsCAT/EMCs loci, respectively. The SSRs data were analyzed using 'PeakScanner' and 'Identity' software. Complex polymorphic bands were observed among chestnut cultivars, which ranged from 1,200 to 300 base pairs in length when (GTG)(5) was used. Amplicon sizes ranged from 76 to 193 base pairs when specific SSRs were used and the number of alleles observed at a locus ranged from 4 to 6. Results obtained from this study will allow for the genetic characterization of the chestnut cultivars and seedling trees currently growing in Michigan, and subsequently will help us establish high quality chestnut plantings for food and fiber production.