Phenotypic variation and heritability
There was a general trend of increasing trait values in the
F2 with latitude, exhibiting latitudinal plasticity of
the measured panicle traits (Figure 3). The violin plot for each trait
at each site displayed approximately normal distribution and
transgressive behavior in the F2 generation. Lowland
genotypes, AP13 and WBC, always had larger values of panicle length (PL
in mm), primary branching number (PBN), and secondary branching number
(SBN) than upland genotypes, DAC and VS16 (Figure 3).
The heritability (h2 ) for PL, PBN and SBN
varied by site (Table 2). The h2 for PL ranged
from 0.20 to 0.71, with an average of 0.46 and values greater than 0.50
at four northern sites. The h2 for PBN ranged
between 0.45 and 0.66 for 9 out of the 10 sites, with Stillwater, OK
(STIL) having low heritability (h2 =0.20). Theh2 for SBN ranged from 0.02 to 0.62, where
Stillwater, OK (STIL) had h2 close to zero
(h2 =0.02), Columbia, MO (CLMB) had low
heritability (h2 =0.15), and four sites had
heritability at approximately 0.50. These changes in heritability by
environment indicate G x E, which primarily is the result of changes in
variances across the common garden environments.
The phenotypic and genetic correlations between traits were generally
positive but varied by site, ranging from 0.21 to 0.63 for phenotypic
correlation and from 0.35 to 0.88 for genetic correlation (Table 3). The
phenotypic correlation between traits across all sites ranged from 0.50
to 0.61. The genetic correlation between PL and PBN across all sites was
close to zero (0.03), while the genetic correlation between PBN and SBN
was high (0.73) (Table 3). Together, these results suggest independence
in panicle length and branching characteristics.