22 JoA•• BerthudFurthermore, if apomixis is controlled bymultiple genes, the probability <strong>of</strong> diffusing thistrait to wild relatives is extremely low. A wildplant would need to receive several genes(probably on several different chromosomes)from the cultivated plant to become apomictic.This transfer would certainly lower its fitnessto a value unacceptable for survival in the wild.If apomixis is under a simple genetic control,diffusion <strong>of</strong> apomixis to landraces and wildrelatives is possible. <strong>Apomixis</strong> reducesrecombination rates and could be perceivedas a danger for conservation <strong>of</strong> geneticdiversity <strong>of</strong> wild relatives and landraces. Inactuality, current genetic diversity is the result<strong>of</strong> a long process <strong>of</strong> domestication, which isstill underway in some regions <strong>of</strong> the world,especially where wild and cultivated plantscontinue to exchange genes, <strong>of</strong>ten within atraditional agricultural system. Somewhatsurprisingly, it is in regions where traditionalagriculture prevails that apomixis could be themost helpful. We know that obligate apomixisis an exception and facultative apomixis ispredominant (Asker 1979). If during thetransfer <strong>of</strong> apomixis to crops, residual sexualityis also transmitted and expressed in the newapomictic crop, we could rely·on the rate <strong>of</strong>recombination inherent in this process togenerate new genetic combinations. Even atlow rates, new combinations may beinteresting to farmers who could select andpropagate them easily. As long as apomixis isnot obligate, landraces can still evolve. It mayalso be possible to introduce new genes from"exotic" and modem sexual varieties. Crosseswill occur only in the proportion k (rate <strong>of</strong>residual sexuality). But if these new productscan be detected by markers or by their hybridvigor, following selection, they could serve asan important source <strong>of</strong> seed for the nextgeneration. The possibility and rate <strong>of</strong>evolution <strong>of</strong> these apomictic varieties willeventually depend upon the rate <strong>of</strong> residualsexuality; therefore, it will be important toconsider this paramet-er when transferringapomixis from wild apomixis donor plants t<strong>of</strong>irst apomictic varieties. This rate <strong>of</strong> residualsexuality may depend on genetic factors.Controlling these factors, in order to adapt thevalue <strong>of</strong> this parameter in new apomicticvarieties, could be extremely useful as we seekto conserve the genetic diversity <strong>of</strong> landracesand allow for their continual evolution.Areas <strong>of</strong> traditional agriculture are repositoriesfor most <strong>of</strong> the genetic diversity <strong>of</strong> crops. Theconservation <strong>of</strong> this diversity is threatened,however, by changes in technical practices thatcan suppress current gene flow and by theintroduction <strong>of</strong> new modern varieties withlimited genetic diversity (e.g., F jhybrids).Producing new varieties from localgermplasm may be advantageous to farmers,and it could be more easily accomplished ifapomixis is incorporated into the breedingscheme (see Toenniessen, Chap.1). In thisscenario, landraces with high genetic diversitywould be maintained in these farmingsystems, thus limiting the diffusion <strong>of</strong> varietieswith low genetic diversity. This diversitywould serve as a reservoir for future evolution.ReferencesAsker, S. 1979. Progress in opomixis resellrch. Heredffos91: 231-40.Asker, S., and l. Jerling. 1992. <strong>Apomixis</strong> in Plonll. Boco Roton, Florida:CRC Press.Bashaw, E.e., M.A. Hussey, and KW. Hignight. 1992. Hybridizotion (n+nand 211+n) <strong>of</strong> farultafive apomidtic species in the Pennise/um agamiccomplex. In/emotionol Journal <strong>of</strong> PIont x;ence 153: 466-70.Barca((ia, G., A. Mazzucato, M. Pezzotti, and M. Fokinelli. 1994.Comporison between isozyme ond RAPD ono~ses to meen aberrantplants in Poo pra/ensis Lprogeny. <strong>Apomixis</strong> News/elfer 7: 29-30.Boyer, RJ. 1987. Evolution and ph~ogenelic relationships <strong>of</strong> theAn/ennorio (Asteraceoe: Inuleoel polyplOid agamic com~exes. BioI.Zen/. bl. 106: 683-98.--.1990. Patterns <strong>of</strong> donal diversity in the An/ennorio raseo(Asteroceoe) po~ploid agamic complex. American Journal <strong>of</strong> B%ny77: 1313-19.Ber1haud, J., M. Borre, and Y. Savidon. '993. Managing genetic resources<strong>of</strong> the agamic genus, Tripsowm exploration, conservation,disfrib~tion. ASA meeting, Gndnnoti, Ohio, Nov. 7-12, 1993.abstract: Pp. 186.Corman, J.G., 1992. Unifying our effOllsla create opom:ctic crops.<strong>Apomixis</strong> News/elfer. 5: 47-50.
<strong>Apomixis</strong> .,d Ih. M..og.....t .f G...tic Dly...~y 23--. 1997. Asynchronous expression <strong>of</strong> duplicate genes inongiosperms moy couse opomixis, bispory, tetraspory, ondpo~embryony. Biological Journol <strong>of</strong> the Unneon Soriety 61: 51-94.Combes, D. 1975. Po~morphisme el modes de reproduction dons 10section des Moximae du genre Ponicum (Graminees) en Afrique.Memoires ORSTOM (Paris) #77.Combes, D., ond J Pernes 1970. Voriations dons les nombreschramosomiques de Panicum maximum en relation avec Ie mode dereproduction. CR. Arad. Sri. Paris 270: 782-85.De Wet, J.MJ. 1968. Diploid·tetroplaid-hoploid eyries and the origin <strong>of</strong>voriobility in Dirhanthium. Evolution 22: 394-397.De Wet, JMJ., ond JR. Harlan. 1970. <strong>Apomixis</strong>, po~ploidy, ondspeciotion in Dirhanlhium. Evolution 24: 270--77.Dujardin, M., and W,w. Hanna 1989. Developing apomictic pearl milletrharocterizotion<strong>of</strong> 0 BC:J plant. Journol <strong>of</strong> <strong>Genetic</strong>s ond Breeding 43:14S-50.Ellstrand, N.e., ond M. Roose. 1987. Pa"erns <strong>of</strong> genotypic diversity inrlonal plant species. American Journal <strong>of</strong> Botany 74: 123-31.Fisher, R.A. 1941. Average excess ond overage effect <strong>of</strong> a genesubstirurion. Ann. Eugen. 11: 53-61Ford, H., and AJ. Richards. 1985. Isozyme variation within and betweenTaroxacum agamospecies in a single locality. Heredity 55: 289-91.Grimanelli, D., O. leblanc, E. Espinosa, E. Peroni, D. Gonzalez de lean,and Y. Savidon. 1998. Non-Mendelian transmission <strong>of</strong> apomixis inmaize- Tripsacum hybrids caused by a transmission ralio distorlion.Heredity 80: 40--47.Hanno, W., M. Dujordin, P. Ozios-Akins, E. Lubbers, and L. Arlhur. 1991Reproduction, cytology, and ferlility <strong>of</strong> pearl millet x Penniselumsquamulatum BC 4plants. Journal <strong>of</strong> Heredity. B4: 213-16.Harlan, JR., M.H. Brooks, D.S. 8argaonkar, and JMJ. de Wet. 1964.Nature and inheritance <strong>of</strong> apomixis in Bathriarhloa and Dirhan/hium.Botanical Gazette 125: 41-46.Harlan, J.R., and JMJ. De Wet. 1975. On 0. Winge and a prayer: theorigins <strong>of</strong> po~laidy. Bot. Rev.41: 361-69.Huff, D.R., and JM. Bara. 1991 Determining genetic origin <strong>of</strong> aberrantprogeny from facultative apomictic Kentucky bluegrass using 0combination <strong>of</strong> flow cytometry and ~Iver·stained RAPD markers.Theare/iral and Applied <strong>Genetic</strong>s 87: 201-208.Kermirle, J.L., and J.O. Allen. 1990. Cross·incompatibility between maizeand teosinte. Maydiro 35: 399-408.Leblanc, D., M.D. Peel, JG. Carman, and Y. Sovidan. 1995.Megasporogenesis and megagametogenesis in several Tripsacumspecies (Poaceae). Americon Journal <strong>of</strong> Botany B2: 57-61Leblanc, 0., D. Grimonelli, H.1. Faridi, J. Berlhaud, and Y. Sovidan. 1996.Reproductive behavior on moize- Tripsacum pa~haploid plants:implications for the transfer <strong>of</strong> apomixis inlo moize. Journal <strong>of</strong>Heredity 87: 108-11.lyman, J.C., and H.e. Elistrand. 1984. donal diver~ty in TaraxacumaHirinale (Asteraceael, an apomict. Heredity 53: 1-10.Marshall, D.R., and A.H.D. Brown. 1981. The evolution <strong>of</strong> apomixis.Heredity47: 1-15.Magie, M., and H. Ford. 19B8. Sexual and asexual Taraxacum species.Biologiral Journal <strong>of</strong> the Unneas Society 35: 16s-68.Nakajima, K., 1. Komatsu, H. Mochizuki, and S. Suzuki. 1979. Isolation <strong>of</strong>diploid and tetraploid sexual plants in Guinea gross (Panicummaximum). Japan Journal <strong>of</strong> Breeding. 29: 228-38.Hogler, G.A. 19B4. Gametophytic apomixis. In B.M. Johri (ed.),&nbryology <strong>of</strong> Angiosperms. New York: Springer-Verlag. Pp. 47S518.Horrmonn, G.A., CL. Quarin, and B.L. Burson. 1989. 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Journal<strong>of</strong> the Ameriran Society <strong>of</strong> Agronomy. 91r-112.Quarin, e.L 1992. The nature <strong>of</strong> apomixis and its origin in Panicoidgrasses. <strong>Apomixis</strong> Newsletter 5: 7-15.Rurishouser, A. 1948. ~eudogamie und po~morphie in der GaNungPotentilla. Arrh. Julius Klaus-Stih Vererbungsforsrh 23: 267-424.Sovidan, Y., and J. Pernes. 1982. Diploid-Ietraploid-diho~oid eyries andthe evolution <strong>of</strong> Panicum maximum Jacq. Evolution 36: 596--600.Stebbins, G.L, and M. Kodani. 1944. Chromosomal varia lion in Guayuleand Moriola. Journal <strong>of</strong> Heredity. Pp. 163-72.Valle, e.B. do, and J'w. Miles. 1992. Breeding <strong>of</strong> opomictic species.<strong>Apomixis</strong> Newsletter 5: 37-47.Volle, C.B. do, and Y. Sovidan 1996. <strong>Genetic</strong>s, cytogenetics, andreproductive biology <strong>of</strong> Brachiaria. In J'w. Miles, B.L Ma~s, ond CB.do Valle (eds.), Brarhiaria: Biology, Agronomy, and Improvement.Coli, Colombia: C1AT-EMBRAPA. Pp.147-61von Dijk, P., ond J. von Damme. 2000. <strong>Apomixis</strong>lechnology and rheparadox <strong>of</strong> sex. Trends in Plant Scienre 5(2): 81-84.Wilkes, H.G. 1967. Tea~nte: the dosest relative <strong>of</strong> moize. Ph.D_disserlation. Bussey Institute, Harvard University, Cambridge,MassachuseNs.
- Page 2 and 3: (over illustration:Pictured is an i
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72 R....11 T. SlMrwoodwe postulate
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74 Rob.rt T. Sherwoodin the gametop
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76 Rokrt T. SHtwoodPerhaps the most
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78 Robe" T. S~erwoodEnvironment pla
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80 Robert T. SherwoodBanaglio, E. 1
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82 Robe" 1. Sherwood---. 1989. Apom
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84 Dcaitl ~11i-, lot To...., .od Di
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88 Oaoitl G
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90 o.lel ~II-, Jo. lob.., aod Diego
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and meiotic or developmental mutant
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94 D..iel Grimallelli-, Jo. Tohme,
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96 10k. G.(o,.,..mechanisms (Figure
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98 Jolo.G.(_explain the existence o
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100 JolI.G.C....parameters affectin
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106 J.hG.eforseveral thousand to a
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108 Jelo.G.(_large linkage group in
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112 a... A. 8icUeI1993). Before the
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118 Ron A. Mlltllstudies of apomixi
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120 I... A. BkbollLeblanc, 0., M.D.
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122 Olivier L.bla.,.ncI A.d,ea M.nu
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158 Yv•• Savid..unreduced polar
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160 Yves SoviclaoBashawet al. (1970
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162 hOI Scrvidao211 = 56 chromosome
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164 r.., SaYid..Transfer of Gene(s)
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166 rves Sqyldaounanswered. However
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Chapter 12From Sexuality to Apomixi
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170 lie. Gros..iklalSgametes and em
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172 Uti Gro....1aosGunning 1990). T
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174 UeIGr.........embryogenesis, wh
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176 U.IGm..lln.apomictic pathway wi
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178 IJeIGr.........development with
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180 Ud Gr....lIoo,(Rhoades and Demp
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182 Ue5Gro........Meiosis is an alm
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184 Uel Gn...lIDo,To date, the phen
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21 0 Ud Gromild.1S--.1982. Nature e
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Chapter 13Induction of Apomixis inS
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214 Uta Praebll aod Rod ScottCrosse
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216 Uta Praektlt.. Rod Scana minori
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