Chapter 5 Genetic Analysis of Apomixis - cimmyt

132 Olivier leblaoc and Aldr.. Mall,,"'ainterference contrast optics, both entailing However, these tests do not require muchconsiderable expense. Stain clearing equipment or technical skill, and can thus betechniques that allow observation of ovule managed everywhere. Their main drawbackdetails under traditional optics are less is that they produce frequent errors becauseexpensive. Molecular markers that cosegregate facultative apomixis occurs more often thanwith apomixis, which enable analysis at earlier previously thought. Moreover, progeny withgrowth stages than cytoembryology, require sexual origin may resemble the mother plantthe development ofspecial plant materials and in morphology, leading to misclassificationprotocols, and the cost of associated supplies and to an overestimation of the degree ofis often beyond the means of many research apomixis. The existence of this gray area ingroups. Moreover, they may not be used with progeny plant classification was reported bymaterials that differ in origin from the Williamson (1976), after extensive progenymaterials used to identify the markers, testing in Paa sp. This makes morphologicalespecially in the case of the highly cross­ progeny tests unreliable when apomixis isspecific RAPDs (Williams et al. 1993). highly facultative, but more efficient asMorphological progeny tests are time- and apomixis expression increases. Early progenyspace-consuming because good descriptors tests using isozymic or molecular markers canare usually expressed in adult plants and a be conducted for apomixis detection on 15-25minimum of 15 to 25 offspring are needed. offspring. Only a few isozyme systems areTable 9.3 Advantages and disadvantages of important procedures for the investigation of modes ofreproduction at the plant and progeny levels. * See Ragot and Hoisington (1993) for RFLP and RAPD costs.Plant level analysesProgeny testsProcedures Cy1oembryo· Molecular markers Auxin lests Chr. counting in Adult Pionts Morphology Fingerprinlinglogy (dearing co·segregating ovaries or seeds Chr. counting'procedures) with apomixis'Information Apomixis type Depends on the Indication of Indication of Off-types of Apomixis idenlification andexpected determination nature of the apomixis apomixis 2n+n and quantification; off-types nature ifand sexual marker(s) expression; expression; n+O nature combined with chromosomepotential identified (to eslimalion of estimation of detection. counting.estimation. date linkage the degree of the degreewith apomeiosisl. parthenogenesis of apomixis.Plant 15 to 100 Already deter­ 100 flowers. 5010100 Apomixis identification:15to 25 offspring.materiak flowers, mined materials ovaries/seeds: Apomixis quantification: at least 100 offspring.required depending on in segregationlhe objectives. for markeridentification.Advantages Easy and Ana~ses can be Easy and quick Easy and Easy if flow Eosy Analyses onquick to performed to perform quick to cylometry young offspringsperform after ear~. after flowering perform after (embryo, possible.flowering. pollination. endosperm,plantlels).Constraints Expensive Preliminary work The auxin lest Expensive nme consu­ nme and space consumming.equipment to determine has been mainly equipment for ming (dassical Morphological tesls: unreliable iffor materials. Use used 10 dale in flow cytometry. methods) or opomixis is high~ focultative.microscopy. of the markers cool-season expensive ifocross accessions grasses. flow cylometryof differentis used.origins? Expensive.