Parthenogenesis induction in diplosporic tetraploidized alfalfa.

Because gametophytic apomixis in alfalfa [lucerne] is strongly correlated with the occurrence of hybridity and poliploidy, bilateral sexual polyploidization (BSP) schemes were adopted for introgressing the diplosporic mutation of PG-F9 at the tetraploid level using unreduced pollen producers of M. coerulea. Tetraploidized F1 plants from BSP were then backcrossed with mutant PG-F9 (employed as unreduced egg donor) and the BC1 progenies screened for level of ploidy, occurrence of diplospory, genetic similarity with diploid parents, and fertility in controlled matings with tetraploid testers of M. sativa. Nine tetraploid BC1 plants out of 15 recovered showed a degree of diplospory ranging from 5.04 to 40.96%. In order to promote parthenogenesis in these mutants, named DTA (Diplosporic Tetraploidized Alfalfa), two methods were adopted: treatments with auxins and crosses after emasculation with M. coerulea. Four plants yielded an average of 5.7 seeds out of 47 flowers treated with NAA, whereas two plants produced an average of 5.6 seeds out of 46 flowers pollinated. These seeds were sown and DNA samples from each plant were analyzed with PCR-based molecular markers. To assess the genetic identity between progenies and the mother plants, two markers per linkage group of an already developed genetic map will be scored. The presence of all selected maternal markers in a single progeny plant will support that seeds were formed by apomixis. Results on the mode of reproduction of DTA plants and the possibility of assembling an apomictic system of seed production in alfalfa are reported and discussed