Variation in vigour and in RFLP-estimated heterozygosity by selfing tetraploid alfalfa: new perspectives for the use of selfing in alfalfa breeding

The effect of selfing on vigour and heterozygosity was analysed in six inde pendent families obtained by recurrent cycles of self-fertilization and sel ection until the S-3 generation. The heterozygosity level, estimated by mea ns of 11 homologous probes, decreased from the S-0 to S-3 generations and w as partially restored in S2XS2 polycrosses. The decreasing trend was influe nced by the inbreeding level of the chosen mother plant in each self genera tion to advance in subsequent selfing, Plant vigour estimated by Dry Matter Yield (DMY) decreased during inbreeding, and phenotypic selection of S-2 i ndividuals seemed to prove effective as the differences in DMY between vigo rous and weak plants were maintained in S(2)xS(2) crosses. No correlation b etween plant vigour and heterozygosity was found between subgroups of vigor ous and weak plants selected within the same S-2 family. Results are discus sed with a view to selecting the best performing and least heterozygous pla nts during inbreeding to isolate useful genes and linkats in superior parti ally inbred parental lines.