Effect of pollen xenia on embryonic development period and embryo cell sizes in Chinese chestnut

Abstract: 【Objective】Xenia is the effect of genes from the male parent on the development of fruit or seeds. Pollen xenia effect was obvious on fruit size, shape, color, flesh quality, peel separation and the ripening period of fruit in Chinese chestnut. However, pollen xenia on embryonic development of Chinese chestnut was rarely reported. This study was undertaken to investigate the effects of pollen xenia on embryonic development, which will provide a theoretical basis for the further study on the development of Chinese chestnut hybrid breeding.【Methods】Chinese chestnut is widely distributed in China.Based on geographical distribution, Chinese chestnut is classified into southern and northern cultivar groups. The eating quality of northern cultivars, including the sweetness and glutinous characteristics, is considered better than that of southern cultivars. In this research, two southern Chinese chestnut cultivars ('Yunfu'and'Yunling') and two northern Chinese chestnut cultivars ('Yanshanhong'and'Yanlong') were chosen for pollen xenia experiment. Two southern and two northern chestnuts used as male parents or female parents were divided into self or cross artificial pollination combination experiment.After 23 days of pollination, the zygote began to divide. Chestnuts were collected on 23 June, 30 June, 8 July, and 15 July, respectively. The samples were placed in a glass bottle containing the fixative solution. The paraffin section technique was used to slice the collected samples and the embryo development at different stages was observed under a microscope employing objective lens in the orders of40× and 100×. For the observed endosperm nuclear cells and cotyledon cells, the size of 10 cells near the zygote was measured and the average value was obtained.【Results】 (1) Among the four varieties tested, female flowers of'Yanlong'had the earliest flowering period, followed by'Yanshanhongli'and'Yunfu', and'Yunliang'had the latest flowering period. Experimental results showed that embryos developed early after they were pollinated with the pollen of the varieties whose fruits developed early in the same orthogonal combination. (2) Multiple comparison indicated that the longitudinal and transverse diameters of nut endosperm cell nucleus showed a tendency of gradual enlargement at different stages. When'Yunfu'was used as a female parent, the transverse and longitudinal diameters of the three pollination treatments all increased like this: first faster and then slower. And when“Yunliang'was used as a female parent in dealing with the three kinds of pollination, performance of transverse and longitudinal diameters in'Yunliang'×'Yunliang'and'Yunliang'×'Yanlong'showed in the following trend: first fast and then slow, while'Yunliang'×'Yanshangong 'was shown as first slow and then quick. (3) There was little difference in the transverse and longitudinal diameter development of cotyledonous cells in the three pollination combinations with'Yunfu'and'Yunling'as the female parents. (4) Although the three diameters of nuts in the cross-pollination group were larger than those in the self-pollination group, chestnut was the most obvious in the pollination combination of'Yunling'♀ and'Yanlong'♂. In summary, in the same orthogonal combination, the embryo development pollinated by pollen of early fruit ripening varieties was also early. The transverse and longitudinal diameters of endosperm nucleus cells in different pollination combinations were significantly different. The transverse and longitudinal diameters of cotyledons were not significantly different among different combinations at the same development stage, and there was no significant linear relationship between the size of mature nuts and the development process of transverse and longitudinal diameters of cotyledon cells.【Conclusion】The results showed that Chinese chestnuts had obvious hybrid advantages. In breeding practice, pollens from early maturing species can be used to produce early maturing nuts, and the taste and size of the nuts can also be improved by crosspollination between northern and southern Chinese chestnuts, which is very significant for fruit quality and the overall economic value improvement.