Among the BC
3
F
3
families, ten were more blight
tolerant than F
1
hybrids (Figure 1), whereas the
remaining BC
3
F
3
families were less tolerant.
The heritability of blight tolerance, which is the
proportion of variation in survival days that is
genetically determined, was 0.37 ± 0.07. These
results help us determine which Meadowview
BC
3
F
2
parents are sufficiently blight-tolerant
to keep and which ones are inferior and need
to be culled from the breeding program.
2018 Correlation between
SSAs and Field Tests
Among the BC
3
F
3
families screened using SSAs, 37
were also evaluated for blight tolerance in field
progeny tests conducted between 2011 and 2016.
A goal of the SSAs this year was determining if
there is a correlation between the blight tolerance
rankings in the 2018 SSAs and field progeny tests.
The advantage of using SSAs for progeny testing
is that results on family average blight tolerance
can be obtained in one year versus four years
in the field. We can also screen higher numbers
of each family per year with the SSA method.
In the SSAs, the survival days measurement for
blight tolerance is negatively correlated with the
average canker severity of the same families
34 CityTREES
Figure 1. "Time to wilt" was the metric by which resistance was measured for 107 BC
3
F
3
families
and controls. Ten families survived as long or longer than F
1
s. No backcross families survived as long
as Chinese chestnut controls h2 = 0.37 ± 0.07
Figure 2. Thirty-seven BC
3
F
3
families screened in 2018
using small stem assays were previously inoculated in
orchard progeny tests. Small stem assay time to wilt date
correlated well with progeny test canker severity data
(r= -0.75 ± 0.30).
