Effects of flower stage and different pollination methods on pollen germination and pollen tube growth in pistil of walnut

Abstract：【Objective】In order to understand factors involved in pollination in walnut, the effects of flower stage and different pollination methods on pollen germination and pollen tube growth in walnut (Juglans regia 'Xinxin 2') were observed in this study.【Methods】J. regia'Xinxin 2'as pistillate plant was pollinated with 3 methods, including natural pollination, artificial self-pollination and artificial cross-pollination with pollen grains from J. regia'Wen185'. The pollinated female inflorescences were excised at different time, and the number of pollens adhered to stigma, pollen germination rate and pollen tube were observed under a fluorescent microscope.【Results】The number of pollen grains on stigma in the female flower during the female blooming was significantly different among pollination method. Pollen grains were hardly observable in the stigma before the stigma had expanded and at thestage when stigma lobes began to separate. The number of pollen grains observed in the stigma at the stage when the stigma lobes expanded to an angle of 15° was significantly smaller than at the stages when stigma lobes expanded to angles of 30° and 45° and when the stigma lobes began to wither. The germination rate of pollen grains attached to the stigma at the stage when stigma lobes expanded to an angle of 30° was higher than at the stage when the stigma lobes began to wither. The temporal patterns of pollen germination rate and the pollen tube growth in the treatments with different pollination methods were significantly different (P < 0.01) . The pollen germinated within 8-36 h. Pollen germination in artificial cross-pollination treatment occurred earlier than natural pollination treatment. After 36 h, there was no difference in germination percentage among the three pollination methods (P > 0.05) . Fertilization occurred 10 days after pollination. In the artificial cross-pollination treatment, pollen germination took place the earliest (8 h) and the time required to complete fertilization was the shortest (10 d) .【Conclusion】The stigma at the stage when its lobes expand to an angle of 45° has the highest compatibility to pollen grains and enables the best growths of pollen tube. Therefore, this flower stage is the best period for pollination. Fertilization in artificial cross-pollination takes place earlier than self-pollination.