Quantitative ovule sterility in Medicago sativa

Abstract

 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 callose deposition, which began during embryo-sac development and affected 81% of 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 demonstrating a sporophytic genetic control. B17 was crossed with P13, a Peruvian plant with 5% callosized ovules, to generate reciprocal F₁ populations, and an F₁ plant (91% callosized ovules) was used to obtain the backcross populations. B17 was also crossed to unrelated, highly fertile, plants. S₁ progenies from B17 and P13 were also studied. All the progeny populations displayed continuous variation for the percentage of sterile ovules, supporting 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 reciprocal crosses. Six progeny plants showing 100% callosized ovules proved to be female-sterile. Ovule sterility could be an important component of the generally observed low realized seed potential in alfalfa.