Apomixis has the potential of cloning plants through seed and thus it gives a unique opportunity in cultivated alfalfa breeding for the selection of superior cultivars with permanently fixed heterosis. Apomixis as a whole has never been detected in the Medicago sativa-corelua-falcata complex, but features of apomixis such as restitutional apomeiosis and haploid parthenogenesis have been documented. Cytological and molecular data have independently provided evidence that diplosporic mechanisms of unreduced egg formation would occur in a diploid spontaneous mutant of M. sativa subsp. falcata named TNE (two-n-eggs). Besides, a morphological and molecular progeny test has previously indicated that apomeiosis in this mutant would not be tightly associated to parthenogenesis. Because gametophytic apomixis has shown to be strongly correlated with the occurrence of hybridity and polyploidy, bilateral sexual polyploidization schemes were adopted for introgressing the diplosporic mutation at the tetraploid level using unreduced pollen producers of diploid M. sativa subsp. coerulea. Tetraploidized F1 plants so obtained were then backcrossed with mutant TNE employed as unreduced egg donor in order to partly recover its genetic background and to assess the inheritance of the meiotic abnormality. Several progenies were screened for level of ploidy, occurrence of diplospory, genetic similarity with diploid parents, and fertility in controlled hybridizations with tetraploid testers of M. sativa subsp. sativa. A total of nine tetraploidized BC1 plants showed apomeiotic megaspores in ovules, as assessed by cyto-histological observations, with a degree of diplospory up to 41%. Since in alfalfa is effective a triploid embryo block that operates in interploidy crosses, their ability of producing apomeiotic embryo sacs containing functional unreduced eggs at the tetraploid level was demonstrated by controlled hybridizations with octoploid pollinators of M. sativa subsp. sativa. Nevertheless, our synthetic mutants named DTA (diplosporic tetraploidized alfalfa), set a few seeds in either wide-crosses or auxin-tests evidencing a null or very low capacity for parthenogenesis of their unreduced eggs. Overall results are presented in details and efforts for assembling an apomictic system of seed production in alfalfa are critically discussed.

Progress in assembling a functional system of apomictic seed production in alfalfa.

BARCACCIA, GIANNI;LUCCHIN, MARGHERITA;
1999

Abstract

Apomixis has the potential of cloning plants through seed and thus it gives a unique opportunity in cultivated alfalfa breeding for the selection of superior cultivars with permanently fixed heterosis. Apomixis as a whole has never been detected in the Medicago sativa-corelua-falcata complex, but features of apomixis such as restitutional apomeiosis and haploid parthenogenesis have been documented. Cytological and molecular data have independently provided evidence that diplosporic mechanisms of unreduced egg formation would occur in a diploid spontaneous mutant of M. sativa subsp. falcata named TNE (two-n-eggs). Besides, a morphological and molecular progeny test has previously indicated that apomeiosis in this mutant would not be tightly associated to parthenogenesis. Because gametophytic apomixis has shown to be strongly correlated with the occurrence of hybridity and polyploidy, bilateral sexual polyploidization schemes were adopted for introgressing the diplosporic mutation at the tetraploid level using unreduced pollen producers of diploid M. sativa subsp. coerulea. Tetraploidized F1 plants so obtained were then backcrossed with mutant TNE employed as unreduced egg donor in order to partly recover its genetic background and to assess the inheritance of the meiotic abnormality. Several progenies were screened for level of ploidy, occurrence of diplospory, genetic similarity with diploid parents, and fertility in controlled hybridizations with tetraploid testers of M. sativa subsp. sativa. A total of nine tetraploidized BC1 plants showed apomeiotic megaspores in ovules, as assessed by cyto-histological observations, with a degree of diplospory up to 41%. Since in alfalfa is effective a triploid embryo block that operates in interploidy crosses, their ability of producing apomeiotic embryo sacs containing functional unreduced eggs at the tetraploid level was demonstrated by controlled hybridizations with octoploid pollinators of M. sativa subsp. sativa. Nevertheless, our synthetic mutants named DTA (diplosporic tetraploidized alfalfa), set a few seeds in either wide-crosses or auxin-tests evidencing a null or very low capacity for parthenogenesis of their unreduced eggs. Overall results are presented in details and efforts for assembling an apomictic system of seed production in alfalfa are critically discussed.
1999
Proc. IV Intl. Herbage Seed Conference.
8887652007
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/178432
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