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Cucurbit Genetics Cooperative Report 6:72-73 (article 36) 1983

Effect of Fruit Thinning on Dry Matter Accumulation and Variability in Cucurbita maxima Winter Squash

Deborah Evans and Brent Loy

University of New Hampshire, Durham, NH 03824

In breeding efforts to develop small-fruited bush strains of C. maxima winter squash, we have encountered problems in obtaining strains with consistently high dry matter in the pericarp of fruit. Preliminary observations suggested that this variability occurred among fruit on the same plant as well as resulting from year to year differences among plants. In the summer of 1982 we compared dry matter content in fruits of a bush and a vine cultivar of C. maxima to ascertain if there were differences among fruit in accumulation of dry matter according to position and time of pollination.

The bush strain ‘Gold Nugget’ and the vine strain ‘Buttercup’ were planted in a bush-vine split plot with five replications and two plants per plot. ‘Buttercup’ plants were allowed to set fruit naturally. ‘Gold Nugget’ received three treatments: natural fruit set, plants thinned to four fruits, and plants thinned to three fruits. Data were obtained on position of fruit on plant and time of pollination.

Fruit thinning significantly increased fruit size and % dry matter of the pericarp (Table 1). Although total fresh weight of fruit decreased with decreased numbers of fruit per plant, the total dry weight of pericarp did not, and, in fact, was significantly greater on plants thinned to three fruits. Fruit size and total fresh weight of fruit per plant varied more on unthinned than on thinned plants; whereas, the variability in fruit dry weight was greatest on thinned plants. Surprisingly, variability in % dry matter, an important quality component, was as high or higher in fruit of thinned as in those unthinned plants.

Table. 1. Effects of fruit thinning on yield components in 'Gold Nugget' squash and a comparison of dry matter accumulation and variability in 'Gold Nugget' (bush) and 'Buttercup' (vine) squash.a


Ave. fruit size (kg)

Ave. fruit fr. wt. per plant (kg)

Ave. fruit dry wt. per plant (kg)

% dry matter pericarp

Gold Nugget





   3 fruit/plant

1.0 ± 0.1

3.1 ± 0.4

0.56 ± 0.10

18.0 ± 2.6

   4 fruit/plant

0.9 ± 0.1

3.5 ± 0.4

0.46 ± 0.08

12.6 ± 1.2

   Natural set (8.2)

0.6 ± 0.1

5.2 ± 1.3

0.45 ± 0.06

 8.6 ± 1.2











   Natural set (8.4)

2.0 ± 0.2

16.7 ± 3.1

4.1  ± 0.7

24.9 ± 1.4

aUnder low density spacing: 3' x 6' (within x between row) for ‘Gold Nugget’, and 6' within row with no guard rows for 'Buttercup'.

Because of the indeterminate and branching growth habit of ‘Buttercup’ as contrasted to ‘Gold Nugget’, fresh and dry weight yields were much higher in the former cultivar. Of more importance from a quality standpoint, % dry matter in the pericarp was higher and variability in % dry matter was lower in ‘Buttercup’ than in ‘Gold Nugget’.

In ‘Gold Nugget’ a significant positive correlation (r = 0.52) was, found between time of pollination and % dry matter with the natural fruit load. We observed a similar relationship in a bush breeding line which normally sets 3 to 5 fruits per plant. Time of pollination did not affect % dry matter in fruit of ‘Buttercup’. In selecting bush genotypes for high dry matter, sampling techniques should be used which take into account the above relationship between date of pollination and % dry matter of pericarp.

Our results to date indicate that multi-fruited bush plants of C. maxima tend to set too many fruit relative to their photosynthetic capacity. This results in low mean dry matter content in the pericarp of fruit. We have selected small-fruited strains which set fewer fruits and exhibit higher % dry matter in the pericarp, but these strains still lack the fruit uniformity desirable in commercial cultivars. Bush cultivars of C. maxima appear most suitable for home gardeners because of their small space requirement. In those bush strains which set numerous fruit, fruit thinning could be recommended for increasing % dry matter and cooking quality of fruits.

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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 1 August, 2007