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.