The American Chestnut Foundation (TACF) is currently developing methods to predict resistance to the chestnut blight fungus based on DNA sequence. This method, called genomic selection, is potentially a rapid and accurate assessment of whether or not American chestnut backcross hybrids inherited genetic variants that confer blight resistance from their Chinese chestnut parents.
Currently, the method for selecting trees with blight resistance is to inoculate them with the chestnut blight fungus and retain only individuals with the smallest and least severe cankers. This method eliminates the most susceptible individuals, but is not accurate enough to make final selections of the most resistant individuals. Variation in chestnut blight canker severity is a function of both the environment and the number of resistance genes that a hybrid tree inherited. Environmental factors that enhance or interfere with the expression of resistance may obscure underlying genetic resistance.
To develop genetic tests for resistance to both chestnut blight and Phytophthora root rot, TACF is mapping regions of the genome inherited from Chinese chestnut by American chestnut backcross hybrids. Our scientists are also scanning the chestnut genome for correlation between DNA sequence variants and disease resistance. Genomic selection holds potential to circumvent the time-consuming and laborious process of inoculating progeny of selection candidates with the chestnut blight fungus to infer their genetic resistance.