Editing Cucurbita (section)

=== Reproductive biology ===

[[File:Peponapis pruinosaCane-12.JPG|thumb|alt=Bee pollinating female ''Cucurbita'' flower|''Cucurbita'' female flower with pollinating [[squash bee]]s]]

All species of ''Cucurbita'' have 20 pairs of [[chromosome]]s.<ref name="rhodes">{{cite journal |last1=Rhodes |first1=A. M. |last2=Bemis |first2=W. P. |last3=Whitaker |first3=Thomas W. |last4=Carmer |first4=S. G. |year=1968 |title=A Numerical Taxonomic Study of ''Cucurbita'' |journal=[[Brittonia]] |publisher=[[New York Botanical Garden Press]] |volume=20 |issue=3 |pages=251–266 |doi=10.2307/2805450 |jstor=2805450 |bibcode=1968Britt..20..251R |s2cid=6973668}}</ref>

Many North and Central American species are visited by specialist [[pollinator]]s in the [[Apidae|apid]] tribe [[Eucerini]], especially the genera ''[[Peponapis]]'' and ''[[Xenoglossa]]'', and these [[squash bee]]s can be crucial to the flowers producing fruit after pollination.<ref name="nee" /><ref name="hurd">{{cite journal |last1=Hurd |first1=Paul D. |last2=Linsley |first2=E. Gorton |year=1971 |title=Squash and Gourd Bees (''Peponapis'', ''Xenoglossa'') and the Origin of the Cultivated ''Cucurbita'' |journal=[[Evolution (journal)|Evolution]] |location=St. Louis, MO |publisher=Society for the Study of Evolution |volume=25 |issue=1 |pages=218–234 |doi=10.2307/2406514 |jstor=2406514 |pmid=28562933}}</ref><ref name="whitbem">{{cite journal |last1=Whitaker |first1=Thomas W. |last2=Bemis |first2=W. P. |year=1964 |title=Evolution in the Genus ''Cucurbita'' |journal=Evolution |volume=18 |issue=4 |pages=553–559 |doi=10.2307/2406209 |jstor=2406209}}</ref>

[[File:Cucurbita maxima Zapallo Plomo semillería Costanzi - flowers detail (masculine) - male flower, some petals and 1 filament removed.jpg|thumb|120px|alt=Male ''Cucurbita'' flower|Male flower, part of the perianth removed, arrows indicating nectar pores]]

When there is more pollen applied to the stigma, more seeds are produced in the fruits and the fruits are larger with greater likelihood of maturation,<ref name="winsor">{{Cite journal |last1=Winsor |first1=J. A. |last2=Davis |first2=L. E. |last3=Stephenson |first3=A. G. |year=1987 |title=The Relationship Between Pollen Load and Fruit Maturation and the Effect of Pollen Load on Offspring Vigor in ''Cucurbita pepo'' |journal=The American Naturalist |volume=129 |issue=5 |pages=643–656 |doi=10.1086/284664 |jstor=2461727 |s2cid=84901190}}</ref> an effect called [[xenia (plants)|xenia]]. Competitively grown specimens are therefore often hand-pollinated to maximize the number of seeds in the fruit.<ref name="rwrobinsoncross">{{cite journal |last=Robinson |first=Richard W. |year=2000 |title=Rationale and Methods for Producing Hybrid Cucurbit Seed |journal=Journal of New Seeds |volume=1 |issue=3–4 |pages=1–47 |doi=10.1300/J153v01n03_01 |s2cid=85158524}}</ref><ref name="stephenson">{{cite journal |last1=Stephenson |first1=Andrew G. |last2=Devlin |first2=B. |last3=Horton |first3=J. Brian |year=1988 |title=The Effects of Seed Number and Prior Fruit Dominance on the Pattern of Fruit Production in ''Cucurbita pepo'' (Zucchini Squash) |journal=Annals of Botany |volume=62 |issue=6 |pages=653–661 |doi=10.1093/oxfordjournals.aob.a087705}}</ref> [[Parthenocarpy|Seedlessness]] is known to occur in certain cultivars of ''C.&nbsp;pepo''.<ref name="robinsonreiners">{{cite journal |last1=Robinson |first1=R. W. |last2=Reiners |first2=Stephen |date=July 1999 |title=Parthenocarpy in Summer Squash |url=http://hortsci.ashspublications.org/content/34/4/715.full.pdf |url-status=live |journal=HortScience |volume=34 |issue=4 |pages=715–717 |doi=10.21273/HORTSCI.34.4.715 |archive-url=https://web.archive.org/web/20151106115239/http://hortsci.ashspublications.org/content/34/4/715.full.pdf |archive-date=2015-11-06 |access-date=2013-11-07 |doi-access=free}}</ref><ref name="menezes">{{cite journal |last1=Menezes |first1=C. B. |last2=Maluf |first2=W. R. |last3=Azevedo |first3=S. M. |last4=Faria |first4=M. V. |last5=Nascimento |first5=I. R. |last6=Gomez |first6=L. A. |last7=Bearzoti |first7=E. |date=March 2005 |title=Inheritance of Parthenocarpy in Summer Squash (''Cucurbita pepo'' L.). |journal=Genetics and Molecular Research |volume=4 |issue=1 |pages=39–46 |pmid=15841434}}</ref>

Critical factors in flowering and fruit set are physiological, having to do with the age of the plant and whether it already has developing fruit.<ref name="stapleton">{{cite journal |last1=Stapleton |first1=Suzanne Cady |last2=Wien |first2=H. Chris |last3=Morse |first3=Roger A. |year=2000 |title=Flowering and Fruit Set of Pumpkin Cultivars under Field Conditions |journal=HortScience |volume=35 |issue=6 |pages=1074–1077 |doi=10.21273/HORTSCI.35.6.1074 |issn=0018-5345 |doi-access=free}}</ref> The [[plant hormone]]s [[ethylene]] and [[auxin]] are key in fruit set and development.<ref name="martínez">{{cite journal |last1=Martínez |first1=Cecelia |last2=Manzano |first2=Susana |last3=Megías |first3=Zoraida |last4=Garrido |first4=Dolores |last5=Picó |first5=Belén |last6=Jamilena |first6=Manuel |year=2013 |title=Involvement of Ethylene Biosynthesis and Signalling in Fruit Set and Early Fruit Development in Zucchini Squash (''Cucurbita pepo'' L.) |journal=BMC Plant Biology |volume=13 |issue=139 |pages=139 |doi=10.1186/1471-2229-13-139 |issn=1471-2229 |pmc=3856489 |pmid=24053311 |doi-access=free}}</ref> Ethylene promotes the production of female flowers. When a plant already has a fruit developing, subsequent female flowers on the plant are less likely to mature, a phenomenon called "first-fruit dominance",<ref name="stapleton" /> and male flowers are more frequent, an effect that appears due to reduced natural ethylene production within the plant stem.<ref name="krupmick">{{Cite journal |last1=Krupnick |first1=Gary A. |last2=Brown |first2=Kathleen M. |last3=Stephenson |first3=Andrew G. |year=1999 |title=The Influence of Fruit on the Regulation of Internal Ethylene Concentrations and Sex Expression in ''Cucurbita texana'' |journal=International Journal of Plant Sciences |volume=160 |issue=2 |pages=321–330 |doi=10.1086/314120 |s2cid=85794143}}</ref> [[Ethephon]], a plant growth regulator product that is converted to ethylene after metabolism by the plant, can be used to increase fruit and seed production.<ref name="rwrobinsoncross" /><ref name="murray">{{cite journal |last=Murray |first=M. |year=1987 |title=Field Applications Of Ethephon For Hybrid And Open-Pollinated Squash (''Cucurbita'' Spp) Seed Production |journal=Acta Horticulturae |volume=201 |issue=201 |pages=149–156 |doi=10.17660/ActaHortic.1987.201.15}}</ref> Although ''Cucurbita'' species can generally produce healthy fruit after pollination from the same plant, [[inbreeding depression]] can significantly reduce seed number and fruit size.<ref>{{citation |author=Inácio, Cardoso |year=2004 |title=Depression by inbreeding after four successive self-pollination squash generations |journal=Scientia Agricola |volume=61 |doi=10.1590/S0103-90162004000200016|hdl=11449/5322 |hdl-access=free }}</ref>

The plant hormone [[gibberellin]], produced in the stamens, is essential for the development of all parts of the male flowers. The development of female flowers is not yet understood.<ref name="lange">{{cite journal |last1=Pimenta Lange |first1=Maria João |last2=Knop |first2=Nicole |last3=Lange |first3=Theo |year=2012 |title=Stamen-derived Bioactive Gibberellin is Essential for Male Flower Development of ''Cucurbita maxima'' L. |journal=Journal of Experimental Botany |volume=63 |issue=7 |pages=2681–2691 |doi=10.1093/jxb/err448 |pmc=3346225 |pmid=22268154}}</ref> Gibberellin is also involved in other developmental processes of plants, such as seed and stem growth.<ref name="sturt">{{cite web |title=Plant Hormones |url=http://www.hsc.csu.edu.au/agriculture/production/3359/plant_hormones_answers.htm |url-status=dead |archive-url=https://web.archive.org/web/20140116140049/http://www.hsc.csu.edu.au/agriculture/production/3359/plant_hormones_answers.htm |archive-date=January 16, 2014 |access-date=January 15, 2014 |publisher=Charles Sturt University}}</ref>

==== Germination and seedling growth ====
[[File:Kabocha (GH) 21June2005 sown 14June.JPG|thumb|alt=Kabocha seedling at seven days age|[[Kabocha]] seedling seven days after being sown]]

Seeds with maximum [[germination]] potential develop (in ''C.&nbsp;moschata'') by 45 days after [[anthesis]], and seed weight reaches its maximum 70 days after anthesis.<ref name="wilsonma">{{Cite journal |last1=Wilson |first1=Mack A. |last2=Splittstoesser |first2=Walter E. |year=1980 |title=The Relationship Between Embryo Axis Weight and Reserve Protein During Development and Pumpkin Seed Germination |journal=Journal of Seed Technology |volume=5 |issue=2 |pages=35–41 |jstor=23432821}}</ref> Some varieties of ''C.&nbsp;pepo'' germinate best with eight hours of sunlight daily and a planting depth of {{convert|12|mm|in|frac=8|sp=us}}. Seeds planted deeper than {{convert|125|mm|in|frac=4|sp=us}} are not likely to germinate.<ref name="oliver">{{Cite journal |last1=Oliver |first1=Lawrence R. |last2=Harrison |first2=Steve A. |last3=McClelland |first3=Marilyn |year=1983 |title=Germination of Texas Gourd (''Cucurbita texana'') and Its Control in Soybeans (''Glycine max'') |journal=Weed Science |volume=31 |issue=5 |pages=700–706 |doi=10.1017/S0043174500070211 |jstor=4043694 |s2cid=182243467}}</ref> In ''C.&nbsp;foetidissima'', a weedy species, plants younger than 19 days old are not able to sprout from the roots after removing the shoots. In a seed batch with 90 percent germination rate, over 90 percent of the plants had sprouted after 29 days from planting.<ref name="horak">{{Cite journal |last1=Horak |first1=Michael J. |last2=Sweat |first2=Jonathan K. |year=1994 |title=Germination, Emergence, and Seedling Establishment of Buffalo Gourd (''Cucurbita foetidissima'') |journal=Weed Science |volume=42 |issue=3 |pages=358–363 |doi=10.1017/S0043174500076621 |jstor=4045510 |s2cid=132074382}}</ref>

Experiments have shown that when more pollen is applied to the stigma, as well as the fruit containing more seeds and being larger (the xenia effect mentioned above), the germination of the seeds is also faster and more likely, and the seedlings are larger.<ref name="winsor" /> Various combinations of mineral nutrients and light have a significant effect during the various stages of plant growth. These effects vary significantly between the different species of ''Cucurbita''. A type of stored phosphorus called [[Phytic acid|phytate]] forms in seed tissues as spherical crystalline intrusions in protein bodies called [[Globoid (botany)|globoids]]. Along with other nutrients, phytate is used completely during seedling growth.<ref name="beecroft">{{cite journal |last1=Beecroft |first1=Penny |last2=Lott |first2=John N. A. |year=1996 |title=Changes in the Element Composition of Globoids From ''Cucurbita maxima'' and ''Cucurbita andreana'' Cotyledons During Early Seedling Growth |journal=Canadian Journal of Botany |volume=74 |issue=6 |pages=838–847 |doi=10.1139/b96-104|bibcode=1996CaJB...74..838B }}</ref> [[Heavy metal (chemistry)|Heavy metal]] contamination, including [[cadmium]], has a significant negative impact on plant growth.<ref name="subin">{{cite journal |last1=Subin |first1=M. P. |last2=Francis |first2=Steffy |year=2013 |title=Phytotoxic Effects of Cadmium on Seed Germination, Early Seedling Growth and Antioxidant Enzyme Activities in ''Cucurbita maxima'' Duchesne |journal=International Research Journal of Biological Sciences |volume=2 |issue=9 |pages=40–47 |doi=10.1139/b96-104|bibcode=1996CaJB...74..838B }}</ref> ''Cucurbita'' plants grown in the spring tend to grow larger than those grown in the autumn.<ref name="fenner2">{{cite journal |last1=Fenner |first1=G. P. |last2=Patteron |first2=G. W. |last3=Lusby |first3=W. R. |year=1989 |title=Developmental Regulation of Sterol Biosynthesis in ''Cucurbita maxima'' L. |journal=Lipids |volume=24 |issue=4 |pages=271–277 |doi=10.1007/BF02535162 |s2cid=37220982}}</ref>