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.