Chapter 5 Genetic Analysis of Apomixis - cimmyt

Geoelk Ao.lysis of Apomi.is 79The results of the maize-TripsoCllnJ Summarybackcrossing effort conform with the idea of a The results of all published studies onrecessive lethal factor linked to a dominant inheritance of apospory are compatible withdiplospory gene (Savidan et al. 1995). No the hypothesis that expression of aposporyapomictic representatives were found in Be 2requires the dominant allele of a major geneprogeny with 211 = 38= 20M+18T chro­ or Iinkat. There is no species for which themosomes produced from F of 211 = 56 hypothesis of a major dominant apospory1=20M+36T chromosomes. See also Grimanelli factor can be ruled out. Limited data availableet al. (Chap. 6) for discussion.for diplosporous species also suggest a singlemaster gene or linkat (Savidan 1989); itsRichards (1996) postulates that lethal recessivepOSSible correspondence to the aposporymutants might occur at loci linked with thelinkat is entirely unknown. Some reportsdominant apomixis locus and accumulate inindicate that degree of expression is regulatedheterozygotic apomictic lines without beingby modifying genes that promote sexuality;expressed. These harmful recessive genes maythe apomixis gene(s) may show dosage effects,be expressed in haploid gametophytes (i.e.,and environment may influence expression.pollen and embryo sacs) resulting in theirSeveral lines of evidence indicate that the wildabortion. The implied corollary is that thetype allele of the apomixis gene plays anapomixis allele is not, of itself, the source ofessential role in cell function and that itsrecessive lethality. The evidence from studiespresence is required for survival of theby Nogler (1984b), Mogie (1988), Sherwood etgametophyte. There is no clear evidence for aal. (1994), and others still points to themajor gene for parthenogenesis independentapomixis gene as being recessively lethal.of the major gene(s) for apospory orSegregation ratios from the facultativediplospory (Nogler 1984a, 1995; Leblanc et al.populations cited above show an absolute lack1995b; Mazzucato 1996). Recombinationof recombination of recessive lethality vis a viswithin the linkat is rare or nonexistent. Thethe apomixis linkat on the male side, but notlinkat encodes sufficient information to directon the female side.the complex sequence of developmentalevents in embryo sac initiation, differentiation,maturation, and function.--.1980. Gametaphytic apomixis: Bashaw, E.C., and KW. Hignight. 1990. GeneReferenceselements and genetic regulation. Hereditas transfer in apomiclic buffelgrass throughAlmgard, G. 1966. Experiments with Poa. III. 93: 277-93. , fertilization of an unreduced egg. Crop Sci.Further studies of Poa longifolia Trin. withAsker, S.E., and LJeding. 1992. Apomixis in 30: 571-75.special reference to its crass with Poa Plan/s. Boca Raton, Florida: CRC Press. Bashaw, E.C., and E.C. Halt. 1956.pratensis L Lantbrukshogskolan Annales 8ashaw, E.C. 1962. Apomixis and sexuality in Megasporogenesis, embryo soc~2: l--64. buffelgrass. (rap Sci. 2: 412-15. development and embryogenesis inAsker, S.E. 1967. Induced sexuality aher--.1980. Apomixis and its application dallisgrass, Paspalum dilatatum, Poir.chronmome doubling in an apomiclic in crap improvement.. In W.R. Fehr and Agran.1. 50: 75l--56.Polentilla argenteo-biatype. Hereditas 57: H.H. Hadley leds.), Hybridization of (rop Bashaw, E.C., A.W. Havin, and E.C. Halt. 1970.339-42. Plants. Madison, Wisconsin: ASA and CSSA. Apomixis, ils evolutionary signi~cance and--.19700. Apomixis and sexuality in thePp.45-63utilization in plant breeding. Proe. I'th Int.Potentilla argentea complex. I. Crosses withBashaw, E.c., and w.w. Hanna. 1990. Apomiclic Grassl. (ongr. Pp. 245-48.ather spe