| Trachycarpus fortunei is an evergreen tree belonging to the genus Trachycarpus in Palmae family with strong resistance to adversity.It is an important economic and ecological tree species in karst area of southwest China,and is widely used in rocky desertification control.However,due to the lack of basic research,the genetic improvement and industrial development of T.fortunei has been limited.In order to reveal the key link and characteristic structure of sexual reproduction of T.fortunei and enrich people’s understanding of the reproductive process of Palmae family,the natural populations of T.fortunei in Huaxi District,Guiyang City,Guizhou Province were selected as the research objects,and the reproductive biological characteristics of T.fortunei were systematically studied by field observation and conventional sectioning techniques.It includes the development process of inflorescence and single flower,flowering dynamic and phenological characteristics,pollen daily vitality,stigma receptivity,pollination system,biological characteristics of seeds and karyotype characteristics of chromosomes.The main conclusions are as follows:(1)The results showed that the leaf primordia of the apical meristem occurred continuously throughout the year,and the angle of divergence was about 1 / 3.With the differentiation of leaf primordium,an inflorescence developed simultaneously at the base of petiole.Its mature structure was a large panicle compound inflorescence formed by multiple branches of spike,with developed vascular system and mechanical tissue.The whole development process of inflorescence can be divided into six main stages: inflorescence meristem formation stage,prophyll development stage,inflorescence axis development stage,single flower morphology differentiation stage,floral sex organ development stage and flowering stage,which lasted for 30 to 35 months.There were multiple inflorescences in the mature trees at the same time,and there was no obvious cycle interval,which was significantly different from that of the temperate dormant trees.(2)It is clear that the development of single flower of T.fortunei was Ⅰ type.The single flower was hermaphroditic at the initial stage of stamen and pistil primordium development,and then parthenogenesis occurred due to the selective abortion of stamen and pistil.Aborted stamens stop developing soon after filament and anther differentiation without anther parietal structure and microspores,and then shrivel and atrophy and lose cellular activity.Aborted pistils gradually stagnate in late flower development,which has double integument and no embryo sac and megaspores.(3)The results showed that the anther parietal structure of fertile stamens in the late stage of secondary sporopoietic cells of palmetto is characterized by secretory tapetum,successive cytokinesis and bicellular pollen.The fertile pistil of T.fortunei was formed by a single detached carpel curling towards the center of radiating symmetry of the flower.It has the characteristic structure of dry stigma,hollow style,basal placentation,anatropous ovule,crassinucellate,double integmental and tegmental tapetum.(4)The results showed that the T.fortunei was strictly dioecious,cross-pollinated and wind-pollinated.The flowering of the T.fortunei population was concentrated in April and lasted for 16 days.The flowering synchronization index was high(0.68±0.11),and there was no missed flowering period.Single plant blooms for 10 days.The inflorescences in the middle and upper part of the plant opened first,and the lower part of the inflorescences opened later,showing the characteristics of stage opening.The inflorescence blooms for 5 to 10 days,showing a "concentrated mass flowering" pattern.The flowering of a single flower lasts 2 to 4 days,and the flowering is not significant.The main characteristic of the flower opening is the maturation and exposure of the sexual organs to ensure the minimum reproductive function.The results also showed that the flowering characteristics of each level of T.fortunei had certain plasticity,which could improve the reproductive success rate and fitness by adjusting their reproductive strategies to cope with adverse environment.(5)It is found that palm fruit is not a drupe in the strict sense because it has no lignified endocarp.Photoneutral seed,there are morphological and physiological dormancy.The average germination time of seeds was 55.8 ± 4.69 d,and the germination type was long distance unsheathed.(6)The results showed that the centromeric type of T.fortunei chromosome was2n=36=24m+12sm,the chromosome length type was 2n=8L+10M2+4M1+14S,the karyotype was "2C",and the nuclear asymmetry coefficient was 60%.No appendages,secondary constrictions and heteromorphic chromosomes were found. |
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