Ovule sterility associated with callose deposition has been recently reported in alfalfa and could contribute to low seed-ovule ratio. The first results of cytological analyses show that no embryo sac develops in sterile ovules and that callose deposition begins just after the meiotic stage, affecting mainly the integumentary tapetum and nucellar cell walls.
Nucellar cells expand to fill the space normally occupied by the embryo sac.
Significant negative correlation was found between the percentage of sterile ovules and seeds per pod in most populations. Selection against ovule sterility should be easy, using a quick stain clearing technique based on callose fluorescence, and effective, due to high heritability. Checking ovule fertility in parental genotypes selected for variety development could help breeders obtain good seed yielding cultivars. Removing at least some of the causes that limit seed potential would be beneficial, since little effort has been put in improving seed yield, and alfalfa can be considered still wild for seed traits. These plants were female sterile when hand crossed with an unrelated male fertile plant.