- Heritability in the narrow sense and in the broad sense, variance components and
correlation coefficients are important genetic parameters in a breeding program. The
estimates of these parameters can provide important information for a breeder in the
selection of parents, the most efficient design for evaluation of seedlings and advanced
selections and the choice of selection strategy to improve many target traits
simultaneously. In addition, histograms showing the distributions of the traits in
offspring may provide additional information about parent combinations for the
improvement of target traits.
The Oregon State University hazelnut breeding program is developing improved
varieties for the kernel market. Estimates of genetic parameters for most traits of interest
are not available. Seventy seven trees representing 41 genotypes and 35 progenies were
used to investigate midparent values and progeny means for 17 traits, including 13 kernel
and nut traits, and 4 phenological traits, for three years.
Estimates for heritability in the narrow sense are all high, ranging from 0.56 for
amount of kernel fiber, and 0.58 for date of opening of female flowers to 0.87 for percent kernel, 0.88 for nut compression index and 0.89 for nut depth. Therefore, progeny means
can be predicted from mid-parent values and response to selection is expected to be rapid
for the improvement of all traits.
The analysis of variance components revealed that genotypic variance accounted
for most of the phenotypic variance. Although significant, the genotype X year
interaction only accounted for a very small part of the phenotypic variance. It suggested
one year's evaluation of genotypes for all traits should be sufficient except for nut
weight, kernel weight, number of nuts per cluster, fiber amount, nut maturity, time of
catkin elongation, and time of opening of female flowers.
Genetic and phenotypic correlation coeficients were large and positive for nut size
traits (nut length, width, depth, nut weight and kernel weight). Phenological traits (date
of opening of female flowers, time of catkin elongation and time of leafing out) were
also highly and positively correlated. But most other traits were uncorrelated with each
other. Therefore, selection of parents with round nuts of medium size, high % kernel,
easily-blanched kernels, and early nut maturity is expected to rapidly improve the
population for all of these traits.
Histograms show that all traits have continuous variation. Transgressive
segregation is very common. For all traits except blanching ability, parent combinations
may be based on midparent values. For the improvement of blanching ability, both
parents should blanch easily.
Because existing statistical packages do not allow easy calculation of genetic
correlation coefficients for tree fruit and nut crops, the use of a spreadsheet to quickly
estimate genetic correlation coefficients is demonstrated.