Studies On Compatibility And Seed Germination Characteristics Of The Distant Hybridization Of Lagerstroemia Indica And Lagerstroemia Excelsa(Dode) Chun

Lagerstroemia indica has beautiful shape,colorful flowers,long flowering period,high ornamental value and wide garden application,but weak resistance to pests and diseases;Lagerstroemia excelsa(Dode)Chun has white flowers,smaller flowers,wide adaptability and strong resistance to pests and diseases.Therefore,the development of Lagerstroemia indica and Lagerstroemia excelsa(Dode)Chun distant cross breeding,the creation of high resistance,high ornamental excellent new varieties,to promote the industrialization of Lagerstroemia indica upgrade development has an important practical and strategic significance.At present,there are barriers to distant hybridization between Lagerstroemia indica and Lagerstroemia excelsa(Dode)Chun,and the mechanism and method of overcoming them are not clear,and the research on affinity and seed germination characteristics of distant hybridization between Lagerstroemia indica and Lagerstroemia excelsa(Dode)Chun at home and abroad is still blank,which restricts the process of distant hybrid breeding between Lagerstroemia indica and Lagerstroemia excelsa(Dode)Chun.In this study,the affinity and seed germination characteristics of distant hybrids between Lagerstroemia excelsa(Dode)Chun and Lagerstroemia indica were investigated using two species of Lagerstroemia,namely ’Ebony Embers’ and ’Ziyun’,as parents.By using orthogonal experimental design,we aimed to screen out the suitable medium formulation for pollen isolation culture,determine the viability of pollen and the pollenability of stigma,and obtain the suitable preservation conditions for pollen;by conducting fluorescence observation on the germination and growth of pollen tubes after pollination,we determined the changes of endogenous hormones in floral organs during fertilization after cross-pollination,and investigated the causes of distant hybridization disorders;through the effects of gibberellin concentration and temperature on the germination of naturally seeded seeds and the growth of seedlings,the germination characteristics of naturally seeded seeds were mastered,which provided a scientific basis and theoretical basis for overcoming the obstacles of distant hybridization and hybrid propagation of Lagerstroemia species in the future.The results of the study are as follows:(1)The results of the study on the viability,preservation and stigma receptivity of Lagerstroemia indica pollen show that the suitable medium formula for Lagerstroemia indica pollen is:sucrose 200g·L-1+boric acid 150mg·L-1+PEG6000 25g·L-1+agar 5g·L-1;Both the long and short stamen pollen of Lagerstroemia indica have viability,but there are differences in the pollen viability of different cultivars.The pollen viability of ’Ebony Embers’ is significantly higher than that of short stamens,and there is no significant difference between the long and short stamens of ’Ziyun’.The pollen germination rate is between 24%and 44%.Drying at 4℃ is a suitable method to preserve crape myrtle pollen with high viability.After 18 days of preservation,the pollen germination rate is 25.33%,which still has high vitality;the pollen viability of Lagerstroemia indica was strong on the first day of flowering,and the pollen germination rate was as high as 87%;It has strong sex,and artificial pollination with fresh pollen from 9:00 to 15:00 on the first day of flowering can improve the success rate of pollination.(2)The results of the study on the seed setting rate and the progeny seedlings of the hybrids of Lagerstroemia excelsa(Dode)Chun and Lagerstroemia indica show that there are obvious differences in the seed setting rate and the number of progeny seedlings between the different Lagerstroemia indica varieties.The highest seed setting rate of the Lagerstroemia indica ’Ebony Embers’♀× Lagerstroemia excelsa(Dode)Chun ♂ was 9.24%,and only 2 hybrid seedlings survived;however,the seed setting rate of the reciprocal cross between Lagerstroemia excelsa(Dode)Chun and Lagerstroemia indica ’Ziyun’ were both lower than 2%,the hybrid seeds did not germinate,and no hybrid seedlings were obtained;The fruiting rate of self-fertilization of Lagerstroemia excelsa(Dode)Chun,Lagerstroemia indica ’Ebony Embers’,and Lagerstroemia indica ’Ziyun’ was high,all exceeding 54%,and obtained a large number of seedlings.The study found that there are serious distant hybridization obstacles in the hybridization of Lagerstroemia excelsa(Dode)Chun and Lagerstroemia indica,especially the hybrid compatibility between Lagerstroemia excelsa(Dode)Chun and Lagerstroemia indica ’Ziyun’ is even lower.(3)The results of the study on the effect of the hybridization of Lagerstroemia excelsa(Dode)Chun and Lagerstroemia indica on the germination and growth of pollen tube show that there is a pre-fertilization barrier in the reciprocal cross of Lagerstroemia excelsa(Dode)Chun and Lagerstroemia indica,and the pollen tube growth of the hybrid combination is abnormal.The pollen tube can pass through the stigma and enter the style,but in the style a large amount of callose is formed,which hinders the continued elongation of the pollen tube,so that the elongation of the pollen tube stops in the style and cannot reach the ovary,resulting in the failure of hybrid insemination.The self-inbred pollen tube of Lagerstroemia indica ’Ebony Embers’ can normally extend to the ovary to complete the fertilization process.(4)The results of the study on the changes of endogenous hormone contents after interspecific cross-pollination of Lagerstroemia excelsa(Dode)Chun and Lagerstroemia indica showed that the fertilization process of Lagerstroemia indica ♀×Lagerstroemia excelsa(Dode)Chun♂ was regulated by ZR,GA3,IAA and ABA.In the later stage of the fertilization process,higher concentrations of ZR,GA3,and IAA,and lower concentrations of ABA are beneficial to promote the continuous elongation of pollen,complete fertilization,and promote the continuous development of flower organs and fruit.In the relationship of endogenous hormone balance,lower IAA/ZR ratio,higher IAA/ABA ratio,ZR/ABA ratio,GA3/ABA ratio,and(GA3+ZR+IAA)/ABA ratio are beneficial to the fertilization process of Lagerstroemia indica ’Ebony Embers’♀× Lagerstroemia excelsa(Dode)Chun ♂ hybrid;higher IAA/ZR ratio,IAA/ABA ratio,GA3/ABA ratio,and(GA3+ZR+IAA)/ABA ratio are beneficial to the fertilization process of Lagerstroemia excelsa(Dode)Chun ♂ × Lagerstroemia indica ’Ziyun’♀ hybrid.(5)The results of the study on the effects of gibberellin and temperature on the germination of Lagerstroemia indica and the growth of seedlings showed that under the constant temperature of 25℃,the optimum concentration of gibberellin for treatment of Lagerstroemia excelsa(Dode)Chun was 200 mg · L-1～300 mg · L-1,and the optimum concentration of gibberellin for treatment of Lagerstroemia indica ’Ebony Embers’ was 50 mg·L-1～500 mg·L-1,and the optimum concentration of gibberellin to treat Lagerstroemia indica’Ziyun’ is 500 mg·L-1;in the day(12h)25℃/night(12h)18℃ variable temperature condition The optimum concentration of gibberellin for treatment of Lagerstroemia excelsa(Dode)Chun was 50 mg·L-1,and the suitable concentration of gibberellin for treatment of Lagerstroemia indica ’Ebony Embers’ was 200 mg·L-1 and 500 mg·L-1.The suitable concentrations of Lagerstroemia indica ’Ziyun’ were 50 mg·L-1 and 500 mg·L-1.Appropriate gibberellin concentration treatment of Lagerstroemia excelsa(Dode)Chun,Lagerstroemia indica ’Ebony Embers’,and Lagerstroemia indica ’Ziyun’ seeds can promote seed germination and promote seedling growth.