The relationship between reproductive growth and blank fruit formation in Corylus heterophylla Fisch

The reason leading to the high blank fruit ratio of Corylus heterophylla Fisch was elucidated by investigating pollen compatibility, ovule and embryo development. It was showed that the female flowers bloomed in the middle of April and the ovary did not develop until 1 month later. In late May, two ovules were found in an ovary. On 22 June, the ovule wall differentiated into integument, and nucellus endosperm were clearly observed in the ovules, suggesting the starting of fertilization event. Globular, heart, torpedo and cotyledon embryo developed step by step from 28 June to 12 July. The ovule grew rapidly in filled fruit since 12 July. Ovule in blank fruit ceased growth from 12 July although the full embryo with cotyledon could be observed. The blank fruit could be distinguished from the filled one for its undeveloped ovule and large amount of parenchyma. There was no significant difference in ovary size between the filled and empty nuts, but the weight of blank nut was only about one half of the filled one. It is concluded that formation of blank fruit of C. heterophylla Fisch is closely related to embryo abortion, but not incompatibility between the pollen and stigma.

► Incompatible obstacle is not the reason inducing high blank fruit ratio in Corylus heterophylla Fisch.
► Female flowers bloomed in the middle of April, while fertilization was completed on 22 June.
► The formation of blank fruit of C. heterophylla Fisch is closely related to embryo abortion.