Quantitative ovule sterility in Medicago sativa

Ovule sterility was found to be associated with callose deposition in B17, a plant with low fertility from the alfalfa cv Blazer XL. The site of callo se deposition, which began during embryo-sac development and affected 81% o f the ovules in mature florets, at random positions in the ovary, appeared to be the embryo-sac wall or the integumentary tapetum. The fertile ovules of B17 transmitted the ovule-sterility trait to the progenies, thereby demo nstrating a sporophytic genetic control. B17 was crossed with P13, a Peruvi an plant with 5% callosized ovules, to generate reciprocal F-1 populations, and an F-1 plant (91% callosized ovules) was used to obtain the backcross populations. B17 was also crossed to unrelated, highly fertile, plants. S-1 progenies from B17 and P13 were also studied. All the progeny populations displayed continuous variation for the percentage of sterile ovules, suppor ting a polygenic control. Narrow-sense heritability estimated by offspring- midparent regression was 0.85. Reduced transmission of the sterility trait through the pollen is hypothesized to explain the difference between recipr ocal crosses. Six progeny plants showing 100% callosized ovules proved to b e female-sterile. Ovule sterility could be an important component of the ge nerally observed low realized seed potential in alfalfa.