Abstract:
A concern which has restricted the use of parthenocarpic pickling cucumbers in the
United States has been firmness of fruit processed by brining. Fruit firmness and defects
of parthenocarpic and nonparthenocarpic pickling cucumbers were evaluated in 1992 and
1993. Fruits were produced with or without pollination by growing plants with or
without floating row covers to exclude pollen vectors. Parthenocarpic cultigens grown
with row covers were not significantly different from nonparthenocarpic cultigens grown
without row covers for fresh fruit firmness in both years. Processed fruit firmness was
similar in 1992, but less for parthenocarpic cultigens in 1993.
Combining ability of a parthenocarpic and nonparthenocarpic set of parents for fruit
firmness and related morphological characteristics were investigated using a factorial
mating design. General combining ability was greater than specific combining ability for
all traits of fresh and most traits of processed fruit, indicating primarily additive
inheritance. Fruit, mesocarp, and endocarp firmness, length, and length:diameter ratio
were positively correlated phenotypically and genetically. Seed cavity diameter and seed
cavity:fruit diameter ratio were positively correlated phenotypically and genetically, but
negatively correlated to all other traits.
Generation means analysis was used to determine the relative importance of genetic
effects in the inheritance of fruit and mesocarp firmness in crosses between
parthenocarpic and nonparthenocarpic pickling cucumbers. The primary genetic effects
in crosses between parents with extreme differences for firmness were additive. Epistatic
effects were also detected, but the nature of these effects could not be determined
because the generations required for such analyses were unavailable. One parental inbred
line was evaluated as a potential donor of favorable alleles for improvement of firmness
using several statistics and was not a source.
The endogenous calcium concentration of cucumber tissue influences tissue softening
and effectiveness of calcium applications for firmness retention during processing.
Genetic differences for fruit calcium concentration in cultigens which differ in fruit
firmness were investigated. Cultigens were not different in fruit calcium concentration,
thus a relationship between fruit calcium concentration and fruit tissue firmness among
cultigens was not shown.
