Effect Of Irradiating Acid Pomelo Pollen With ⁶⁰Co-γ Ray On Fertility And Quality Of Majia Pomelo

Citrus maxima（L.）Osbeck cv.Majiayou is a special variety in Guangfeng district.Its fruit size is large,its flesh is pink,juicy and refreshing,and its sugar content is lower,so it is popular among consumers.But the common Majia pomelo has more seeds,about120-200 seeds per fruit,which seriously affects its commodity and market competitiveness.In this study,sour pomelo pollen was irradiated with ⁶⁰Co-γray,and then pollinated to Majia pomelo,which gets the seedless fruit successfully.In this study,the acid pomelo pollen was irradiated by ⁶⁰Co-γray,at different doses.a comprehensive evaluation of fruit quality and developmental physiology was carried out,It is expected that ⁶⁰Co-γray irradiation dose suitable for production extension will be obtained.Produce a seedless and better quality fruits of Majia pomelo.While the mechanism of inducing Majia pomelo was explored from cytology and molecular level.It provides a reference for the study of seedless mechanism of fruit and the production of seedless pomelo.The results are as follows:1.With the increase of radiation dose,fruit setting rate is decreasing.There was no significant difference between the CK and 100 Gy fruit setting rate at fruit ripening,but the setting rate of CK was significantly higher than that of 600 Gy and 1000 Gy,and the1000Gy was significantly higher than 1400 Gy.During the whole fruit development,the transverse diameter and longitudinal diameter of each radiation treatment were slightly lower than that of CK,1400Gy was the smallest,which was significantly lower than CK,but there was no significant difference between 100 Gy 600 Gy and 1000 Gy and CK.The seeds of mature fruits of different treatments were observed.The results showed that the seeds of the control fruits with large and full,partial degeneration of 100 Gy seeds,the seeds of the fruits treated with 600 Gy and 1400 Gy were small and dry,and as the dose of radiation increases,the total number of seeds is gradually decreasing.2.The results of fruit quality analysis showed that the fruit became smaller,malformed and the thickness of pericarp increased when the dose of radiation was higher than that of normal fruit,as 1400 Gy.However,when the dose of radiation was lower,the number of full seeds was still more,as 100 Gy.Except for the slight decrease in fruit weight and volume（about 100 g）,there was no significant decrease in other quality at the dose of600-1000 Gy.3.In the first 2 weeks after pollination,the content of endogenous hormones in young fruits increased rapidly,and the growth promoting hormone in the control was significantly higher than that in the radiation treatment.In physiological fruiting stage,the growth promoting hormone in the seeds treated with radiation was significantly lower than that in the control.On the contrary,the growth promoting hormone in the pulp treated by radiation was significantly higher than that in the control,and the IAA content in the pericarp of the irradiated fruit was significantly higher than that of the control.At the stage of fruit expansion,the ratio of（IAA+GA₃+ZR）/ABA in the peels and flesh of the control and irradiated fruits was at a higher level,which was the reason why the fruit that seeds abortion after irradiation could expand normally.4.The germination rate of pollen and the elongation of pollen tube were gradually decreased with increasing doses of radiation.However,there was no significant difference between CK and 100 Gy,600 Gy,1000 Gy,and the pollen germination rate and elongation of pollen tube was significantly lower than CK and 100 Gy.The pollen treated by radiation can still germinate on the stigma,and the stigma,style and ovary do not prevent the pollen tube from elongating,and the pollen tube can elongate into the ovule.After 5 days of pollination,the cross section of the ovary was cut,and a large number of pollen tubes were observed to reach the ovary,and the number of pollen tubes in the 1000 Gy elongated to the ovary was significantly reduced.With the increase of pollen radiation dose,the fluorescence intensity of pollen chromosome is decreasing.Compared with the control,there was a significant decrease of 1000 Gy and 1400 Gy.The results showed that the DNA double helix structure and chromosomes were damaged after pollen radiation.5.The process of embryo development was observed by paraffin section.The results showed that at 1 weeks after pollination,polar nuclei were fertilized,the endosperm immediately began to divide,free nuclei were produced and proliferated.The free nucleus of CK was filled with the whole embryo sac at 4 weeks after pollination,while the 1000Gy endosperm showed partial degeneration.At 7 weeks after pollination,the control embryo sac appeared cytoplasms,while 1000 Gy embryo sac developed slowly or stopped,the free nuclear endosperm in embryo sac degenerated and even the embryo sac became hollow.At 10 weeks after pollination,the embryo of the control embryo sac developed to the cotyledon embryo,but no embryo development was observed in the 1000 Gy embryo sac.The endosperm had completely degenerated and the embryo sac was atrophied,showing a narrow and hollow shape.6.From Majia pomelo cloned two genes related to embryonic development,named CmWOX2 and CmFIE.The results of bioinformatics analysis of two genes show that the c DNA sequence of CmWOX2 gene is 1177 bp and contains an open reading frame of750bp,encoding 249 amino acids.The c DNA sequence of CmFIE gene is 1235 bp and contains an open reading frame of 1110 bp encoding 369 amino acids.Spatio-temporal expression analysis of CmWOX2 and CmFIE genes in Majia pomelo show that CmWOX2gene was expressed in the seeds,roots,stems and leaves,the highest expression was found in seeds,followed by roots and stems,and the lowest in leaves.The expression of CmWOX2 gene in CK was always higher than 1000 Gy during seed development.CmFIE gene was expressed in the seeds,roots,stems and leaves,the highest expression was found in seeds,followed by stems and leaves,and the lowest in roots.The expression of CmFIE gene in CK was always lower than 1000 Gy during seed development.