Chapter 5 Genetic Analysis of Apomixis - cimmyt

complex) of interest. The design of breedingschemes that approach "optimum"efficiency-genetically and economicallywilldepend, as well, upon the cost andreliability of the method(s) available to assessrep rod ucti ve mode in segrega tingpopulations.An important obstacle in the recurrentselection programs is the difficulty ofachieving a full generation each year. Mostattributes of interest in perennial Brachiariaspp. are difficult or impossible to reliablyassess in a single season. Seed dormancy,which is typical in tropical wild grasses, alsodelays the breeding cycle and poses anobstacle that has not been overcome, even atthe experimental level. A detailedunderstanding of the factor(s) causingphysiological dormancy in Brachiaria seeds isessential to the rational design of dormancybreakingtreatments. In vitro techniques ofembryo rescue were developed in Brazil, andRodrigues-Otubo et al. (2000) established theage and culture medium for first generationinterspecific hybrids of Brachiaria. Embryosthat were drawn for use 9-12 days afterpollination presented the highest percentageof direct regeneration, although survival rateswere clearly genotype dependent. Embryorescue resulted in significantly highernumbers of hybrid plants being recoveredReferencesAsker, S.E., and J. Jerling 1992. Apomixis inplonts. Boca Raton, Florida: CRC Press.Boshaw, E.C 19BO. Apomixis ond ~s applicationin crop improvemenl. In W.R. Fehr ond H.H.Hadley (eds.l, Hybridization of (rap Plants.Madisan, Wisconsin: American Society ofAgronomy Press. Pp.45-63.Bashaw, E.C., and C.R. Funk. 1987. Apomicticgrosses. In W.R. Fehr led.l, Principles of(ultivar Development, Vo1.2. New York:Macmillan Publishing Co. Pp. 40-82.Batisto, LA.R, and R. Godoy 2000.Caracteriza~iio preliminar e sel~iia degermoplasmo do genero Paspolum paraprodu~iio de forragem. Rev. Bros. Zaotec.,29(1): 23-32.Bogdon, A.V. 1977. Tropical Posture and fodderPlants. New York: longmon.Burson, B.l. 19B3. Phylogenetic investigotions ofopomictic Paspolum dilatatum ond relotedsptl(ies. In Pree. XIV Int. Grossi. (angr.,lexington, Kentucky, 19B1. Boulder,(olorodo: Westview Press. Pp. 170-73.--.1989. Phylogenetks of opomicti