Western SARE Project Number, FW06-042

Published Research on Summer Squash

My results compared with published research results:

1.  Harvesting mini squash yielded 2 -3 times more squash numbers than harvesting large squash.

2.  Why does this occur?  (Resource partitioning in squash)

3.  Patty pan squash are more productive for mini squash than zucchini types. Yellow squash plants are more productive than green squash plants.  Sunburst is particularly productive for mini squash.

4.  References
Table of Contents 
 

1.  Harvesting mini squash yielded 2 -3 times more squash numbers than harvesting large squash.

Researchers get similar results.  Plant ecologists studied flower production in Cucurbita pepo L., ssp. Texana (A. Gray) Filov, a wild progenitor of cultivated squash.  Pistilate (female) flowers and their immature fruits were removed the day after bloom so that the squash fruit did not develop on treated plants, whereas squash fruit was allowed to mature on untreated plants (Avila-Sakar et al. 2001). 

This procedure is similar to mine.  I harvested mini squash within a day or two of flower bloom.  I harvested larger squash  about a week after bloom, not as long as in the research studies.

In another study buds were covered with a bag just before the flower opened, to prevent pollination.  Flowers on fruitless plants were left unpollinated whereas flowers on plants with fruits were hand pollinated (Krupnick et al. 1999).  Fruits aborted after about 6 days on the fruitless plants, but they grew to their maximum size in about 18 days on the plants with fruit.

In both studies, treated plants without developing fruit produced 1.8 – 2 times more pistillate flowers (i.e., mini squash) than untreated plants (Krupnick et al. 1999; Avila-Sakar et al. 2001)

Published research results contents
Table of Contents 

2.  Why does this occur?

Plant ecologists argue that “fruit production is costly to plants in terms of carbon and mineral nutrients that, otherwise, could be used for further growth, defense, or pollen production and dispersal.  Consequently, the failure of flowers to initiate and/or produce mature fruits (e.g., because of lack of pollination, or flower predation) should free resources for growth, defense, and additional flower production.” (Avila-Sakar et al., 2001; see also Stephenson, 1992). 

Research with Cucurbit plants such as squash and cucumber confirm these predictions.  Plants obtain carbon, a building block for growth, through photosynthesis in leaves.  Carbon dioxide from the air is converted into sugar and/or starch using sunlight as a source of energy.  Cucumber plants that were not allowed to flower or set fruit showed more vegetative growth than did cucumber plants with a single growing cucumber fruit (Pharr et al., 1984).  Leaves on plants with a fruit showed signs of a higher rate of photosynthesis (carbon exchange), greater accumulation of carbon, and more export of carbon from the leaves.  Starch levels in leaves in the morning were high in plants without fruits, but low in plants with fruits.   Apparently starch that had accumulated in leaves during the day was moved from the leaves to the fruit at night.  As a result, cucumber fruits grew faster at night than during the day.  (Pharr et al., 1984).  A similar pattern is likely in squash plants.

Similarly, treated plants of Cucurbita pepo L., ssp. texana, (flowers removed after bloom, or not pollinated)  produce twice as many branches, longer internodes, and more nodes per day compared with untreated plants (fruits allowed to mature).  This means that treated plants, which don’t need to provide resources for fruit growth, can use their resources to grow faster and larger than untreated plants. (Krupnick et al. 1999; Avila-Sakar et al. 2001).  With more branches and nodes, the plant also produces more pistillate flowers, and thus more mini squash.

The researchers argue that the plant should also have responded to the absence of fruit production by producing more staminate (male) flowers in order to assure reproduction by pollen dispersal.  Staminate buds increased on treated plants as compared with untreated plants, as expected, but staminate buds on treated plants were more likely to abort before bloom (Avila-Sakar et al. 2001).

Ethylene production appears to be involved in the control of the rate of flower production.  Krupnick et al. (1999) measured ethylene concentrations in the hollow stems between nodes of treated and untreated plants of Cucurbita pepo ssp. texana.  In both treatments, ethylene concentrations were greatest inside the stems just below the tips of branches – where new growth takes place.  Branches with two or more smaller developing fruit had the lowest ethylene concentrations.  When the fruits reached their largest size 18 days after pollination ethylene concentrations were highest.  Young developing fruits apparently inhibit ethylene production, which decreases production of new pistillate flowers.  Ethylene concentrations increase again when the squash fruits reach their maximum size and are no longer a resource sink.

These results were corroborated when ethylene concentrations were experimentally increased by injecting the gas into the hollow stems of Cucurbita texana (Krupnick et al. 2000).  Branches that were injected with ethylene produced more pistillate buds than control branches, and marginally had more developing fruits than control branches.

3.  Patty pan squash are more productive for mini squash than zucchini types.
    Yellow squash plants are more productive than green squash plants. 
    Sunburst is particularly productive for mini squash.

In my experiment, the yellow patty pan variety “Sunburst” was the most productive both at a large size, and especially as mini-squash, in terms of number of squash produced.  It also produced the greatest cumulative yield in grams among the plants harvested as mini-squash.  The yellow zucchini “Butterstick” was the least productive in numbers for mini squash but it was more productive than the green varieties when harvested as a larger squash.  The green zucchini, variety “Cash Flow” was the least productive in numbers in my experiment.

A study of hydroponic greenhouse production for baby squash tested 19 squash varieties, and found “Sunburst” to be the most productive (Shaw and Cantliffe, 2005).  Patty pan squash types in general produced the most baby squash.  Yellow summer squash types were the next most productive, while green Zucchini were the least productive for baby squash. 

In the greenhouse study squash were harvested three times a week.  Squash that were too large to be “baby” were a measure of the potential loss of baby squash if harvests were not sufficiently frequent.  The green zucchini variety “Revenue” produced the greatest yield of large fruits when harvested 3 times a week, suggesting that it should be harvested daily for optimal baby squash yields.

References

Avila-Sakar, G., G. A. Krupnick, and A. G. Stephenson.  2001.  Growth and resource allocation in Cucurbita pepo ssp. texana:  Effects of fruit removal.  Int. J. Plant Sci. 162(5): 1089-1095.

Krupnick G. A., K. M. Brown, and A. G. Stephenson.  1999.  The influence of fruit on the regulation of internal ethylene concentrations and sex expression in Cucurbita texana.  Int. J. Plant Sci. 160(2): 321

Krupnick G. A., G. Avila, K. M. Brown, and A. G. Stephenson.  2000.  Effects of herbivory on internal ethylene production and sex expression in Cucurbita texana.  Functional Ecology 14:215-225.

Pharr DM, SC Huber, HN Sox 1985.  Leaf carbohydrate status and enzymes of translocate synthesis in fruiting and vegetative plants of Cucumis sativus L. Plant Physiol. 77:104-108.

Shaw, N. L. and D. J. Cantliffe.  2005.  Hydroponic greenhouse production of “Baby” squash:  Selection of suitable squash types and cultivars.  Hort. Technology 15: 722-728.  Read the article 

Stephenson, A. G.  1992.  The regulation of maternal investment in plants.  In C. Marshall and J. Grace, Eds.  Fruit and Seed Production, Aspects of development, environmental physiology and ecology.  Cambridge University Press.  pp. 151-171.