Abstract:
The easy picking characteristic, expressed as low pod detachment force (PDF),
offers a way to decrease pod damage in bush green beans mechanically harvested for
processing and fresh market, and makes hand picking easier and faster. This study was
undertaken to examine inheritance in a cross of two green bean cultivars, one of which is
grown extensively in the Willamette Valley for processing and the other of which is
unparalleled for its low PDF.
A preliminary investigation of the two parental bush bean cultivars showed that
PDF of 'Easy Pick' was significantly lower than '91G' at all stages of pod maturation.
The average PDF of 'Easy Pick' varied less over seasons and environments than that of
'91G'. The sampling window was determined to be a week or less in duration once pods
reached harvest maturity. This is important because pod detachment force changes rapidly
as pods become overmature whether or not pod size changes are apparent.
Generation means analysis was used to determine the relative importance of
genetic effects in the inheritance of pod detachment force in plantings made on two dates.
The primary genetic effects were additive, but in Planting Two dominance effects were
also evident. Epistatic effects fit a digenic inheritance model with five parameters.
Parameter estimates for the dominance and dominance x dominance genetic effects in the
two planting dates were of opposite sign indicating the predominant type of non-allelic
interactions are mainly of the duplicate kind. The exact nature of these effects could not
be determined because the generations required for such analyses were not grown in the
same year.
Estimations of heritability and response to selection were calculated from the
sample variances of generation means from six generations grown in 1992, and variance
component estimates from one hundred F₃ families grown in 1993. Narrow sense
heritability was calculated at 59% and 54% for 1992, and 83% for 1993. The regression of
F₃ progeny onto F₂ parents provided a heritability estimate of 27 ± 4.5%. Selection
response estimates indicated the overall F₃ mean of 13.8 ± 5.7 Newtons (N) could be
reduced 2.4-4.0N from family selection in the F₃ generation.
