Study on the Pollen Tube Introduction and Ovule Abortion after Cross-pollination in Medicago sativa, Coronilla varia and Lotus cornioulatous

PurposeLeguminous forages Medicago sativa, Coronilla varia and Lotus cornioulatous are typical allogamy. Ovule abortion reduced the seeds numbers per pod, and actual seed production is much lower than their potential seed production. But fundamental data related to pollen tube introduction and embryo development after pollination are still lack.

MethodUsing controlled pollination method, pollen tube introduction and embryo development were observed in M. sativa, C. varia and L. cornioulatous using fluorescence microscope. And random abortive position of seed in one pod was also collected and analyzed in field trial.

ResultThe stigmas of these three leguminous forages were receptive at the stage of dehiscence, and cuticles of stigma were mechanical barrier as pollen tubes penetrating the style. In M. sativa, pollen grains germinated 2 h after pollination and pollen tube reached the ovary after 8 h. The potential rate of ovule fertilization was up to 75% and remained unchanged 24 h after pollination. In C. varia and L. cornioulatous, pollen tubes reached the ovule 4 h after pollination, and the potential rate of ovule fertilization reached 96% and 100% 8 h after pollination, respectively. Even then, the percentage of seed abortion in M. sativa, C. varia and L. cornioulatous were still higher as 87.67%, 78.00% and 81.33%, respectively. Pollen tube growth and introduction were different in three leguminous forages. Although style lengths of C. varia and L. cornioulatous were longer than that of M. sativa, pollen tubes grew quicker in these two legumes. In M. sativa, C. varia and L. cornioulatous respectively, and random abortive position of seed in one pod was also observed. These results indicated that number of pollen tubes arrived in embryo sac in M. sativa, C. varia and L. cornioulatous could meet the demand of double fertilization.

ConclusionThe numbers of pollen grains loaded on the stigma as well as pollen tube introduction were not the limited factors for seed set, and ovule abortion could be due to embryo development restriction after fertilization in these leguminous forages.