Dry Matter Accumuilation and Productivity in Bush and Vine Strains of Winter Squash

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Cucurbit Genetics Cooperative Report 5:40-41 (article 20) 1982

C. E. Broderick and J. B. Loy
University of New Hampshire, Durham, N.H. 03824

The bush phenotype facilitates conventional row culture and manageability of winter squash, however, there is little information regarding comparative photosynthgetic efficiency and productivity between bush and vine forms of C. maxima.

In 1980 and 1981, field experiments were carried out to compare yields and the partitioning of dry matter in a bush and vine strain of winter squash. ‘Blue Hubbard’ was selected as the vine strain because of its vigor and high yielding capability. The bush strain (30-11-31-9) was a large-fruited, vigorous inbred which normally sets one fruit per plant with close spacing.

‘Blue Hubbard’ and 30-11-8-1 were about equally productive at the 5,600 plants/ha density (Table 1) a spacing shown to be near optimum for ‘Blue Hubbard’. Highest yields for the bush strain occurred at the highest planting density, however, fruits were small and often misshapen, and exhhibited lower percent dry matter at this density. A plant density of about 10,000 plants per hectare is considered optimum for the bush strain, but this could vary depending on location, plant vigor, and time of flowering. Percnet dry matter was low in both bush and vine strains in 1981 due to powdery mildew infestation in the spacing trial.

Table 1. Yield of a bush strain (30-11-8-1) at different plant densities as compared to yield of ‘Blue Hubbard’ planted at near optimum plant density.

1980

1981

Plant Density

pls./ha

kg/ha

Fr.Wt.

kg/pl

Fr.Wt.

kg/ha

Fr.Wt.

kg/ha

Dry Wt.

Kg/pl

Fr.Wt.
Bush

22,000 (0.3 x 1.5 m)

 77,000 3.7 74,800 5,310 3.5

11,000 (0.6 x 1.5 m)

 70,300 6.6 61,500 4,551 5.5

7,400 (0.9 x 1.5 m)

 64,600 9.0 55,300 4,313 7.7

5,600 (1.2 x 1.5 m)

 61,300 10.6 52,200 4,594 9.2
Vine

5,600 (1.2 x 1.5 m)

 57,300 10.4 50.700 4,867 8.7

Above-ground dry matter acumulation was initially similar in ‘Blue Hubbard and 30-11-8-1 plants grown under nono-competitive (low density) spacings (Table 2). With the onset of multiple secondary and tertiary branching in vine plants, total dry matter rose rapidly. Peak dry matter occurred earlier in the bush strain, and dry matter actually declined between 10 to 12 weeks from transplanting, due to early fruit maturity and onset of leaf senecence. Net assimilation rate (NAR) and harvest index were higher in the bush strain. This together with the rapid leaf canopy development of the bush strain under high density planting probably contributed to its high productivity.

Table 2. Dry matter accumulation and distribution in bush and vine strains of winter squash grown at low density planting.

Sample Times (Weeks from Transplanting

Total Plant Dry Wt.

NARy

g/dm2 leaf

% Dry Wt.

Fruit/Total
Bush
Vine
Bush
Vine
Bush
Vine
4 59 67 1.0 0.8 — —
6 725 978 1.6 1.6 17.8 3.2
8 2555 2514 2.4 1.9 — —
10 3125 8174 3.7 2.5 — —
12 2575 9471 5.7 2.8 69.6z 57.0z

yNet assimilation rate (cumulative).
zEquivalent to harvest index (includes both green and mature fruit of ‘Blue Hubbard).