Study On Flowering Biology And Breeding System Of Carya Illinoensis 'Shaoxing' In Huanjiang County

'Shaoxing',a thin shell hickory,has entered its flowering and fruiting period since it was introduced into Guangxi from Yunnan Province.However,it has many problems,such as low seed setting rate,low yield,serious falling flowers and fruits,which seriously restrict the process of poverty alleviation and prosperity of people in mountain area.The process of flowering and pollination is an important part of plant fruiting.In order to study the effects of flowering biology and breeding system on the seed setting of Carya illinoensis' Shaoxing',the flower bud differentiation,flowering process,stigma receptivity,pollen vigor,storage and pollination were studied,in order to provide scientific basis for artificial regulation and intervention of its seed setting.The results are as follows:1.The differentiation of male flower bud in 'Shaoxing' has experienced six stages:morphological differentiation,scale differentiation,bract differentiation,stamen primordium differentiation,stamen primordium differentiation and anther differentiation.The differentiation of female flower bud has five stages: the initial stage of morphological differentiation,the stage of inflorescence formation,the stage of pistil involucre formation,the stage of pistil formation and the stage of pistil development.The differentiation of male and female flower buds needs to go through two growth seasons.The morphological differentiation starts in the first ten days of May,and then enters the dormancy period in the last ten days of October.In the middle and late March of the second year,it continued to differentiate into mature male and female gametophytes,no abnormal development of male and female flower buds was found,and the flower structure was complete.2.'Shaoxing' is a monoecious flower,which does not secrete nectary and has no special smell.The growth and development of male and female flowers are basically synchronous,they all start to sprout in the late March,and the male flowers end in the early May and thefemale flower stigma withers,and the florescence of male and female flowers is similar to that of the full florescence.The growth of male flower bud experienced seven stages: bud germination stage,bract cracking stage,calyx cracking stage,anther yellowing stage,powder scattering stage,anther blackening stage and floret abscission stage.The growth of female flower bud has experienced seven stages: bud germination stage,leaf development stage,"delta" stage,"H" stage,"V" stage,"I" stage and withering stage.The peak period of male and female flowers falling was in the full bloom period,and the male flowers all fell after the powder scattering,and the female flowers remained 66.67%.3.During the period of powder dispersal,the pollen activity of 'Shaoxing' changed from high to low as follows: the peak of powder dispersal > the beginning of powder dispersal >the end of powder dispersal > the end of powder dispersal,the pollen activity of Shaoxing was the highest in the period of full bloom;the pollen activity of 'Shaoxing' during the period of powder dispersal decreased with the prolongation of the time of dry in the shade,and the pollen activity of 'Shaoxing' during the period of full bloom decreased the slowest with the prolongation of dry in the shade;the storage conditions of low temperature and dry were favorable to 'Shaoxing' The change of pollen vitality with time under different storage conditions was as follows:-80? sealed dry >-80? sealed >4? sealed dry > 4?sealed > normal temperature sealed dry > normal temperature sealed.The stigma can be given in V-type and I-type periods,which coincide with the flowering period when the pollen activity of male flowers is the strongest.4.The results of OCI value,P/O value and pollination test of 'Shaoxing' are different,but all of them prove that the breeding system of 'Shaoxing' is heterosexual.The OCI value is 3,which means self compatibility and sometimes pollination is needed;the P/O value is7234,which means specific cross;The results of pollination test showed that it was a mixture of selfing and heterogamy,and there might be apomixis.5.The pollen germination speed and pollen tube growth speed of 'Shaoxing' female flowers in different pollination ways are basically similar.After 4 hours of pollination,only a small amount of pollen grains germinated on the stigma;after 12 hours,the pollen grains began to germinate;after 24 hours,the pollen tube entered the style,after 48 hours,it entered the guide tissue and grew downward;after 96 hours of pollination,it began to grow along the embryo sac.Although the female flowers treated with sulfuric acid paper bags in'Shaoxing' had no pollen germination,they still had fruit,which indicated that there might be no fusion propagation.In the process of pollination,no obstacle was found in the natural state and the female flowers treated with net bags.The pollen grains can germinate on the stigma and the whole pollen tube can enter the embryo sac.Therefore,the serious falling of flowers and fruits has nothing to do with the fertilization process.6.The fruit setting rate and fruit bearing rate of 'Shaoxing' artificial pollination were lower than that of natural pollination.It was observed from the fluorescence microscope that the pollen grains of artificial pollination can germinate on the stigma and the pollen tube can reach into the embryo sac,which proved that artificial pollination is an effective auxiliary pollination method,but the sulfuric acid paper bag has a great influence on the growth of fruit,resulting in low fruit setting rate and fruit bearing rate of artificial pollination.7.The main pollinators in 'Shaoxing' are Episyrphus balteatus de Gee.,Apis cerana,Aulacophora indica,Micraspis satoi,etc.but none of them are effective pollinators.At the same time,through the observation of the amount of male flowers' daily powder dispersal and the 14.12% seed setting rate in the treatment of net bags,the main pollinators in'Shaoxing' are wind pollinators,and the transmission efficiency of wind pollinators is affected by male flowers' powder dispersal Period,climatic conditions,wind direction,etc.To sum up,the male and female flowers of the introduced C.illinoensis 'Shaoxing' from Huanjiang are well developed,the stigma is receptive,the pollen activity is high,and the amount of pollen is sufficient.The pollen can successfully germinate on the stigma and the pollen tube can successfully extend to the embryo sac through wind media transmission.Therefore,its flowering and pollination process has no direct relationship with its low seed setting rate and low yield.