Chapter 5 Genetic Analysis of Apomixis - cimmyt
Chapter 5 Genetic Analysis of Apomixis - cimmyt
Chapter 5 Genetic Analysis of Apomixis - cimmyt
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Ge..tk Aoaly,ls <strong>of</strong> Apomixi, 73the hypothesis <strong>of</strong> one tetraploid genedominant for apomixis, with all sexual parentsassigned genotype aaaa and all apomictsassigned genotype Aaaa.Brachiaria (Gramineae). Valle and coworkers(1991, 1992, 1993, and Chap. 10) conductedextensive studies <strong>of</strong> Brachiaria along the lines<strong>of</strong> Savidan's (1981) guineagrass program. Theresults pointed to a single dominant genedetermining apospory with genotypes <strong>of</strong> aanafor the colchicine-induced tetraploid sexualparents and Aaaa for the aposporoustetraploid parents.Bipolar AposporyRanunculus (buttercup, Ranunculaceae).Nogler (1984b) crossed diploid sexual R.cassubicifolius with tetraploid apomictic R.megacarpus (Figure 5.1). Four fertile triploidfacultatively aposporous progeny wereobtained and used to initiate three generations<strong>of</strong> reciprocal backcrossing to the sexual diploid.Nogler deduced that apospory is caused by adominant factor A (designated A- in Nagler1984b), the wild allele <strong>of</strong> which (a) (designatedA+ in Nogler 1984b) does not enhanceapospory. Dominance <strong>of</strong> A is incomplete andadditive. Furthermore, A, when homozygousrnRanunculus cassuhicifolius = ex M = R. mcgacarpuslevel <strong>of</strong> fl deS"'" <strong>of</strong>p polyploidy 2x aposory4xd' A A ••Iplant;;,obtainedBC,la l'JDB II hybrid: n-ndihaploid: n+O8 m hybrid: ::n + nmaternal: 2" .... 0aa [Aaa] aaa Aa41 aa aaa Aaa (mal.).....• trisomic hybrid: 1n=179'~9~9Q~~~~r "aa A a (mat.) a a A a a DIHAPlOIOS a a a A a a (m~t.) A a a a ao rn·~~·.·.·.·.. Da 0 Aa D U E"~13 0 , 5 D D 2 ~ 21 24 9 ·.... cc·7217" 1S 16 , ..... 1 I / " / 2942J& 23 + 5 veg. 66 7~~~~II!c-3 0 c-=l ~ 0EJ c........=::! L....3 ., 61 0 , 16 0 J& 208 a A a a II A a (maL) A a aFigure 5.1 Genealogical tree <strong>of</strong> the cross Ranuncu!us cassubicilo!iu s =C, 2x =16, meiotic (sexual) x R.megacarpus =M. 4x =32, partially aposporous (Utotally" apomictic) and the different backcrosses withthe sexual parent C. The number <strong>of</strong> plants obtained, the level <strong>of</strong> polyploidy, the approximate degree <strong>of</strong>apospory, and the genotype are indicated for each <strong>of</strong>fspring.Reproduced with permission <strong>of</strong> the publisher, Birkhouser·Yerlog AG, Basel, Switzerland. From Nagler, G.A. 19B4. <strong>Genetic</strong>s <strong>of</strong> opospory in apomicticRanunculus auricomus. Y. Conclusion. Botanica Helvetica 94: 411-422. Updated by G.A. Nagler (personal comm.) and Nogler (1995). See Nogler(I 984b) for details.
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