2.4 Family 52-124 Parent and Progeny Phenotyping
In order to identify regions of the Populus genome associated with biotic stress, a variety of fungal pathogens and insect herbivore species were surveyed in the WVU Morgantown plantation site.Melampsora sp. leaf rust (Figure 1a) and Sphaerulina musiva fungal leaf spot symptoms (Figure 1b) were scored on a 0-3 scale of disease severity, with 0 indicating absence of symptoms and 3 indicating high degree of pathogen leaf damage, in the 2008 growing season for all 1353 tree canopies. In the fall of 2014, stem canker symptoms caused by the same fungus Sphaerulina musiva (Figure 1c) were scored on a 0-5 disease severity scale for a subset 498 unique genotypes and a total of 580 trees. Upon further examination of field conditions for S. musiva disease severity it was determined that none of the progeny displayed complete resistance. The original 0-5 scale was binarized with scores from 2.5-5 scaled to 1 and 0-2 scaled to 0. The new scale indicated the progression of infection with 1 specifying severe canker development and 0 indicating less aggressive canker symptoms.
Two abundant species of galling aphid were also surveyed during the 2016 growing season. To equalize the biomass surveyed for the aphid insect observations on each tree, branches of equal diameter were selected for insect counts and the remaining branches in the canopy were not surveyed. Tree canopy presence or absence for the petiole galling aphidPemphigus populitransversus (Figure 1d) and the branch galling aphid Mordwilkoja vagabunda (Figure 1e) was recorded for 201 unique genotypes and a total of 218 trees. For all of the damage scores in every survey year, 0 indicated a complete absence of fungal or insect presence in tree canopy.
In early August 2017 at the Westport site full canopies were scored by counting galls of the leaf folding sawfly Phyllocolpa sp. (Figure 1f), on 534 unique genotypes and a total of 1020 trees. To estimate productivity of individuals and confirm that availability of resources did not drive insect attraction or feeding, main stem diameter in millimeters was recorded for all trees to be used as a covariate in the analysis.