Editing Sweet corn (section)

==Cultivars==
{{Main|List of sweetcorn varieties}}
Open pollinated (non-[[Hybrid (biology)|hybrid]]) corn has largely been replaced in the commercial market by sweeter, earlier hybrids, which also have the advantage of maintaining their sweet flavor longer. ''su'' cultivars are best when cooked within 30 minutes of harvest. Despite their short storage life, many open-pollinated cultivars such as 'Golden Bantam' remain popular for home gardeners and specialty markets or are marketed as [[heirloom seed]]s. Although less sweet, they are often described as more tender and flavorful than hybrids.{{Citation needed|date=January 2021}}

===Genetics===
{{hatnote|In the following text, lowercase gene names indicate the recessive, loss-of-function mutants. The UniProt links provided are for the regular wild-type genes.}}
[[File:Sweet White Corn.jpg|thumb|200px|Cut white sweet corn. [[Shoepeg corn|"Shoepeg"]] is a popular cultivar from the 1900s.]]

Early cultivars, including those used by Native Americans, were the result of the mutant ''su'' ("sugary") or ''su1'' ({{UniProt|O22637}}) [[allele]] of an [[isoamylase]].<ref name="RJSch"/> They contain about 5–10% sugar by weight.{{Citation needed|date=January 2021}} These varieties are juicy due to the [[phytoglycogen]] content, but they lose sugar quickly after harvest, with the content halving in 24 hours.<ref name=ARWT>{{cite web |last1=Ragusea |first1=Adam |last2=Tracy |first2=William |title=How science saves sweet corn |url=https://www.youtube.com/watch?v=IIVG54wNPd0 |website=YouTube |access-date=30 January 2022 |language=en |date=August 24, 2021}}</ref>

''Supersweet corn'' are cultivars of sweet corn which produce higher than normal levels of sugar developed by [[University of Illinois at Urbana–Champaign]] professor John Laughnan.<ref name="DLLarson"/> He was investigating two specific [[gene]]s in sweet corn, one of which, the ''sh2'' mutation ({{UniProt|P55241}}, a [[Glucose-1-phosphate adenylyltransferase]]), caused the corn to shrivel when dry.  After further investigation, Laughnan discovered that the endosperm of ''sh2'' sweet corn kernels store less starch and from 4 to 10 times more sugar than normal ''su'' sweet corn.  He published his findings in 1953, disclosing the advantages of growing supersweet sweet corn, but many corn breeders lacked enthusiasm for the new supersweet corn due to the seed shiveling reducing germination rate.<ref name=ARWT/>

Illinois Foundation Seeds Inc. was the first seed company to release a supersweet corn and it was called 'Illini Xtra Sweet', but widespread use of supersweet hybrids did not occur until the early 1980s. The popularity of supersweet corn rose due to its long shelf life and large sugar content when compared to conventional sweet corn.<ref name=ARWT/>  This has allowed the long-distance shipping of sweet corn and has enabled manufacturers to can sweet corn without adding extra sugar or salt.{{Citation needed|date=January 2021}} Breeding has resolved the germination rate issue, but it is still generally true that ''sh2'' corn is less juicy than their ''su'' counterparts. ''sh2-i'' ("shrunken2-intermediate") cultivars under development exploits a different mutation on the same gene to try and create varieties that are both juicy and sweet.<ref name=ARWT/>

The third gene mutation to be discovered is the ''se'' (or ''se1'') for "sugary enhanced" allele, responsible for so-called "Everlasting Heritage" cultivars, such as 'Kandy Korn'.  Cultivars with the ''se'' alleles have a longer storage life and contain 12–20% sugar.{{Citation needed|date=January 2021}} The gene for ''Se1'' has been located.<ref>{{cite journal |last1=Zhang |first1=Xia |last2=Mogel |first2=Karl J. Haro von |last3=Lor |first3=Vai S. |last4=Hirsch |first4=Candice N. |last5=De Vries |first5=Brian |last6=Kaeppler |first6=Heidi F. |last7=Tracy |first7=William F. |last8=Kaeppler |first8=Shawn M. |title=Maize sugary enhancer1 ( se1 ) is a gene affecting endosperm starch metabolism |journal=Proceedings of the National Academy of Sciences |date=8 October 2019 |volume=116 |issue=41 |pages=20776–20785 |doi=10.1073/pnas.1902747116|pmid=31548423 |pmc=6789923 |bibcode=2019PNAS..11620776Z |doi-access=free }}</ref>
[[File:Sweet Corn.JPG|200px|thumb|Cooking turns yellow sweet corn golden]]

All of the alleles responsible for sweet corn are [[recessive]], so it must be isolated from other corn, such as field corn and [[popcorn]], that release pollen at the same time; the [[endosperm]] develops from genes from both parents, and [[heterozygous]] kernels will be tough and starchy. The ''se'' and ''su'' alleles do not need to be isolated from each other. However supersweet cultivars containing the ''sh2'' allele must be grown in isolation from other cultivars to avoid cross-[[pollination]] and resulting starchiness, either in space (various sources quote minimum quarantine distances from 100 to 400 feet or 30 to 120 m) or in time (i.e., the supersweet corn does not pollinate at the same time as other corn in nearby fields).{{Citation needed|date=January 2021}}

Modern breeding methods have also introduced cultivars incorporating multiple gene types:
*''sy'' (for ''synergistic'') adds the ''sh2'' gene to some kernels (usually 25%) on the same cob as a ''se'' base (either homozygous or heterozygous)
*''augmented sh2'' adds the ''se'' and ''su'' gene to a ''sh2'' parent
Often seed producers of the ''sy'' and ''augmented sh2'' types will use brand names or trademarks to distinguish these cultivars instead of mentioning the genetics behind them.  Generally these brands or trademarks will offer a choice of white, bi-color and yellow cultivars which otherwise have very similar characteristics.{{Citation needed|date=January 2021}}

===Genetically modified corn===
[[Genetically modified maize|Genetically modified sweet corn]] is available to commercial growers to resist certain insects or herbicides, or both.  Such transgenic varieties are not available to home or small acreage growers due to protocols that must be followed in their production.<ref name="ncga">{{cite web|title= Insect Resistance Management Fact Sheet For Bt Corn|url= http://www.ncga.com/managing-bt-technology|access-date= 2015-06-03|publisher= National Corn Growers Association|archive-date= 2015-05-09|archive-url= https://web.archive.org/web/20150509045144/http://www.ncga.com/managing-bt-technology|url-status= dead}}</ref>