Preliminary study on seed abortion of Whangkeumbae pear cultivated in the greenhouse

Abstract: 【Objective】The Whangkeumbae pear had high early yield and good quality, and when cultivated in the greenhouse, it could prolong the fruit supply period and increase the economic benefits to fruit growers. However, in the production, it was found that the fruit setting rate of Whangkeumbae pear cultivated in the greenhouse was low, the incidence of malformed fruit was high, and most of the dropped and malformed fruits were seedless. Previous studies found that although Whangkeumbae pear had little or no pollen, the pistil could develop normally, and the fruit setting rate could be improved by artificial pollination. However, under the greenhouse cultivation conditions, abnormal temperature regulation was easy to cause abnormal development of ovules and embryo sacs, which caused seed abortion. So, by comparing the development of ovule and embryo sac in the same phenological period of Whangkeumbae pear cultivated in the greenhouse and open field, and combing with the pattern of temperature change, this paper preliminarily discussed the cause of seed abortion of Whangkeumbae pear cultivated in the greenhouse.【Methods】This paper investigated and recorded the pattern of temperature change from bud break to flowering of Whangkeumbae pear cultivated in the greenhouse and open field, and took Whangkeumbae pear under two cultivation conditions as test materials. The flower buds from germination stage to anthesis stage were sampled, and the development process and morphological characteristics of ovules and embryo sacs of Whangkeumbae pear during this period were compared and observed by paraffin sectioning. The ovule and embryo sac size of Whangkeumbae pear at flowering stagewere measured with a micrometer. The fruit setting rate was calculated 20 days after anthesis stage, and the seed abortion of fruits during maturation period was investigated.【Results】The seed abortion rate of Whangkeumbae pear cultivated in the greenhouse was 62.0%, which was significantly higher than that cultivated in the open field (7.0% ). And its fruit setting rate was 21.5%, which was significantly lower than that cultivated in the open field (51.5%). Under the condition of open cultivation, the abortion rate of Whangkeumbae pear seeds was only 7%, with an average of 9.3 normal seeds in each fruit, and seeds were found in five ventricles. Under greenhouse cultivation, the abortion rate of Whangkeumbae pear seeds was as high as 62%, and each fruit had only 3.8 seeds on average, and only 2.7 ventricles had seeds. Comparing the temperature under two cultivation conditions, it was found that the maximum temperature in the greenhouse during the day was generally higher than that in the open field. The average maximum temperature in the greenhouse from bud break to flowering was from 19.6 ℃ to 22.9 ℃, while the open ground was from 14.3 ℃ to 18.6 ℃. Especially 7 days before flowering, the average maximum temperature in the greenhouse during the day was as high as 26.0 ℃, but the open ground was only 19.9 ℃. The unsuitable high temperature treated at the condition of greenhouse cultivation accelerated the flowering speed of Whangkeumbae pear. As a result, the time from bud break to flowering of Whangkeumbae pear cultivated in the greenhouse was 3 days shorter than that cultivated in the open field. At the same time, the embryo sac could not mature at anthesis stage, 50% of the embryo sac was still at single nucleus embryo sac and bi-nucleate embryo sac stage, and 11.1% of the embryo sac was at tetra-nuclear embryo sac stage. When Whangkeumbae pear cultivated in the open field entered the flowering stage, 73.3% of the embryo sacs completed differentiation, but the rest were in different multi-nucleated embryo sac stage, and single nucleus, bi-nucleate and tetra-nuclear embryo sac stages were not detected. In the comparative observation on ovule and embryo sac sections of Whangkeumbae pear, it was also found that the length and width of embryo sac of Whangkeumbae pear under greenhouse cultivation (42.9 μm, 21.8 μm) were less than those under open ground cultivation (78.4 μm, 32.9 μm), and the coefficient of variation was large.【Conclusion】The high temperature treatment before flowering accelerated the flowering speed of Whangkeumbae pear, which resulted in delayed embryo sac development, and the degree of embryo sac development was not synchronized with the flowering period. The retardation of Whangkeumbae pear embryo sac development at anthesis stage was the important reason for high seed abortion and low fruit setting rates in the greenhouse.