Cotton Growth and DevelopmentGlenL.Ritchie,ResearchCoordnatorCraig W.Bednarz,Cotton PhysiologistPhilip H.Jost and Steve M. Brown,Extension AgronomistsDownload and Organized by: Li ShaochangJan.24, 2005
Cotton Growth and Development Glen L. Ritchie, Research Coordinator Craig W. Bednarz, Cotton Physiologist Philip H. Jost and Steve M. Brown, Extension Agronomists Download and Organized by: Li Shaochang Jan. 24, 2005
TableofContents1.Introduction52. Inside the Seed3. Germination and Seedling Development.2.34.TheCotyledonsandFirstTrueLeaves5.SoilEffectsonGerminationandEarlyRootGrowth46.RootDevelopment.7.The Meristems568.VegetativeGrowth9.LeafandCanopyDevelopment710.TheSourcetoSinkRelationship.811.DevelopmentofFruitingandVegetativeBranches12.FormationoftheCottonBudfromSquaretoBloom91013.TheCottonFlower14.StagesofFlowering...101115.NodesAboveWhiteFlowerandCutout1216. Defoliation and Harvest Timing.1317.Fruit Shedding..1318. Boll Development.19.Yield Distribution..141520.Heat Units or DD6S21.Summary16-
ii Table of Contents 1. Introduction . 1 2. Inside the Seed . 2 3. Germination and Seedling Development. 2 4. The Cotyledons and First True Leaves . 3 5. Soil Effects on Germination and Early Root Growth . 4 6. Root Development. 4 7. The Meristems. 5 8. Vegetative Growth. 6 9. Leaf and Canopy Development . 7 10. The Source to Sink Relationship. 7 11. Development of Fruiting and Vegetative Branches . 8 12. Formation of the Cotton Bud from Square to Bloom. 9 13. The Cotton Flower. 10 14. Stages of Flowering. 10 15. Nodes Above White Flower and Cutout .11 16. Defoliation and Harvest Timing . 12 17. Fruit Shedding. 13 18. Boll Development . 13 19. Yield Distribution. 14 20. Heat Units or DD60s. 15 21. Summary. 16
1.IntroductionDomestic cotton has a unique origin and history among cultivated crops. The wildancestors of modern cotton species wereperennial vines that inhabited several distinctgeographic areas,including Africa, Arabia, Australia and Mesoamerica. During the past severalcenturies, people native to these regions developed four distinct species of cultivated cotton,including upland cotton (Gossypium hirsutum L), the primary species grown in the UnitedStates.Despitethe selective breeding effortsof humans,manyof thewild characteristics ofcottonhave notbeenremoved,making cottonmanagementdifficultandunique.Wild cotton is atropical perennial plantwith an indeterminatefruiting habit,meaningthat itcontinues to produce new foliage even after it begins to create seed.Despite its inherentperennial growth habit, however, cotton is managed as an annual crop plant, and growers try toproduceasmuch lintand seed aspossible.Continued vegetativegrowthafterflowering divertsthe plant's energy away from lint and seed production, so the perennial nature of even modemcultivarsopposesourcurrentproductionsystemThecottonplantalsoproducesfruitontwo differenttypesof branches,eachuniqueingrowth habit,further complicating crop management. In addition,cotton growth is very sensitiveto temperature and soil conditions. As in other crops, producers use chemicals in cotton tocontrol weeds and insects, but cotton is unique in that crop growth must also be regulated andeventuallyterminatedbychemicalmeans.Understandingthegrowthanddevelopmentofthecotton plant helps producers grow a high-yielding, high quality crop.Thefollowing discussion is intended to provide applicable information on the growth anddevelopment of the cotton plant.The Georgia Cotton Production Guide (updated annually)is anexcellent data source for the agronomic inputs required for producing cotton. The productionguide and other useful cotton links can be found on the Universityof Georgia Cotton Web Pageathttp:l/www.griffin.ugaedu/caes/cotton
1 1. Introduction Domestic cotton has a unique origin and history among cultivated crops. The wild ancestors of modern cotton species were perennial vines that inhabited several distinct geographic areas, including Africa, Arabia, Australia and Mesoamerica. During the past several centuries, people native to these regions developed four distinct species of cultivated cotton, including upland cotton (Gossypium hirsutum L.), the primary species grown in the United States. Despite the selective breeding efforts of humans, many of the wild characteristics of cotton have not been removed, making cotton management difficult and unique. Wild cotton is a tropical perennial plant with an indeterminate fruiting habit, meaning that it continues to produce new foliage even after it begins to create seed. Despite its inherent perennial growth habit, however, cotton is managed as an annual crop plant, and growers try to produce as much lint and seed as possible. Continued vegetative growth after flowering diverts the plant’s energy away from lint and seed production, so the perennial nature of even modern cultivars opposes our current production system. The cotton plant also produces fruit on two different types of branches, each unique in growth habit, further complicating crop management. In addition, cotton growth is very sensitive to temperature and soil conditions. As in other crops, producers use chemicals in cotton to control weeds and insects, but cotton is unique in that crop growth must also be regulated and eventually terminated by chemical means. Understanding the growth and development of the cotton plant helps producers grow a high-yielding, high quality crop. The following discussion is intended to provide applicable information on the growth and development of the cotton plant. The Georgia Cotton Production Guide (updated annually) is an excellent data source for the agronomic inputs required for producing cotton. The production guide and other useful cotton links can be found on the University of Georgia Cotton Web Page at http://www.griffin.uga.edu/caes/cotton
2.Insidethe SeedAmaturecottonseed containsall oftheorgansnecessarytoproduceasmallseedling.Theseed is pointed on one end (theChalazamicropyle) and rounded on the other(thechalaza).Thetipof theprimaryroot,orradicle,facesthemicropyleand the precursors of thestemandGossypolGlandcotyledons are plainly visible withinthe seed (Figure 1).CotyledonThe chalaza istheprimary site ofEpicotylwater and oxygen absorption duringHypocotygermination. The tip of the primaryroot, or radicle, is the first part of theplantto emergethroughthemicropyleRadielThe cotyledons that will nourish thenew seedling are folded inside theMicropyleseed, with the hypocotyl below themFigure1.Asmall, dormant seedlingrests insideamatureready toelongateandpushtheseed. When the seedling emerges, the radicle wil be thethesoil.Theseedlingthroughprimary root,the hypocotyl will bethe stem underthe.cotyledons,andtheepicotylwillbethestemabovethegossypolglands visiblethroughout thecotyledonsfromwhichshootgrowthoccursinside of the seed are also visible inthe tissues of the growing plant.3.GerminationandSeedlingDevelopmentGermination begins as the seed absorbs water and oxygen through its chalaza afterplanting.Thewaterswellsthedormanttissues,andcellgrowthanddivisionbegintotakeplaceTheradicleemergesthroughthemicropyle,turnsdownward,andgrows deeperintothe soil,providing a taproot that will supply water and nutrients throughout the life of the plant (Figure 2aand b). The hypocotylelongates from the radicle and forms an arch or crook that begins to pushupthroughthesoil,abriefperiodoftenreferredtoasthe“crookstage"(Figure2c)Seedling emergence normally takes place 4 to 14 days after planting. At the soil surface,thehypocotyl straightens and pulls thefolded cotyledons out of the soil (Figure2d),a processknown as epigeal germination.Afterthe cotyledons are pulled through the soil surface,theyunfold and expose the epicotyl and the apical meristem, or growing point, which will be thesourceof subsequent growth (Figure2e-f).Atthispoint, germination and seedling emergencearecompleteandtheplantbegins itsactivevegetativegrowth.2
2 Figure 1. A small, dormant seedling rests inside a mature seed. When the seedling emerges, the radicle will be the primary root, the hypocotyl will be the stem under the cotyledons, and the epicotyl will be the stem above the cotyledons from which shoot growth occurs. 2. Inside the Seed A mature cotton seed contains all of the organs necessary to produce a small seedling. The seed is pointed on one end (the micropyle) and rounded on the other (the chalaza). The tip of the primary root, or radicle, faces the micropyle, and the precursors of the stem and cotyledons are plainly visible within the seed (Figure 1). The chalaza is the primary site of water and oxygen absorption during germination. The tip of the primary root, or radicle, is the first part of the plant to emerge through the micropyle. The cotyledons that will nourish the new seedling are folded inside the seed, with the hypocotyl below them ready to elongate and push the seedling through the soil. The gossypol glands visible throughout the inside of the seed are also visible in the tissues of the growing plant. 3. Germination and Seedling Development Germination begins as the seed absorbs water and oxygen through its chalaza after planting. The water swells the dormant tissues, and cell growth and division begin to take place. The radicle emerges through the micropyle, turns downward, and grows deeper into the soil, providing a taproot that will supply water and nutrients throughout the life of the plant (Figure 2a and b). The hypocotyl elongates from the radicle and forms an arch or crook that begins to push up through the soil, a brief period often referred to as the “crook stage” (Figure 2c). Seedling emergence normally takes place 4 to 14 days after planting. At the soil surface, the hypocotyl straightens and pulls the folded cotyledons out of the soil (Figure 2d), a process known as epigeal germination. After the cotyledons are pulled through the soil surface, they unfold and expose the epicotyl and the apical meristem, or growing point, which will be the source of subsequent growth (Figure 2e-f). At this point, germination and seedling emergence are complete and the plant begins its active vegetative growth
Figure 2.Germination and early seedling development.Rootgrowthdominatestheearlygrowthoftheplant.4.TheCotyledonsandFirstTrueLeavesThecotyledons (Figure 3)serve adual role ingermination.Before they unfold, they supplystoredfoodtothegerminatingseedling.Afterthecotyledonsunfold,theyproducechlorophyll,becomegreen,andproduceenergythroughphotosynthesis.Theapical meristememergesatthe base of the cotyledons,and all further vegetative andreproductive growth of the plantoccursthroughthemeristemsCotyledonCotyledonstTrueFigure3.Thecotyledonsarestorageorgans thatFigure4.The first true leaf emerges about7daysareformedintheseedandemergefromthesoilafterseedlingestablishment.Fromthispointon,theallvegetativeandasleaf-likestructuresoriented oppositeeachmeristemswillproduceother on theseedlingstem.Thecotyledonsreproductivestructuresontheplant.provide nutrients for the seedling. The apicalmeristem emerges through the cotyledons andwill be the source of new growth as the plantmatures.3
3 Figure 2. Germination and early seedling development. Root growth dominates the early growth of the plant. 4. The Cotyledons and First True Leaves The cotyledons (Figure 3) serve a dual role in germination. Before they unfold, they supply stored food to the germinating seedling. After the cotyledons unfold, they produce chlorophyll, become green, and produce energy through photosynthesis. The apical meristem emerges at the base of the cotyledons, and all further vegetative and reproductive growth of the plant occurs through the meristems. Figure 3. The cotyledons are storage organs that are formed in the seed and emerge from the soil as leaf-like structures oriented opposite each other on the seedling stem. The cotyledons provide nutrients for the seedling. The apical meristem emerges through the cotyledons and will be the source of new growth as the plant matures. Figure 4. The first true leaf emerges about 7 days after seedling establishment. From this point on, the meristems will produce all vegetative and reproductive structures on the plant