Study On The Characteristics Of Autotetraploid Of Plumbago Auriculata Lam.

Plumbago auriculata Lam.is a perennial evergreen semi-shrub native of South Africa,which has good ornamental and medical value.Based on artificially induced polyploid is an effective breeding technology which can change the biological characteristics of plants,create new garden germplasm materials,and develop new varieties.In this study,the autotetraploid Plumbago auriculata Lam.came from previous trials.Using diploid as control,the field agronomic traits and main physiological characteristics of autotetraploid were observed,and the differences in morphological growth,flowering characteristics,photosynthetic characteristics,temperature tolerance and content of secondary metabolite plumbagin were compared and analyzed,for assessing the value of polyploid breeding.The research results have important practical significance for the cultivation and promotion of its new varieties.The main findings are as follows:（1）Compared with the diploid,the leaves of the autotetraploid plants became larger,thicker,greener,more round,and obvious leathery.The internodal distance became shorter,basal stems became thicker,plant width became narrower,and more anti-lodging.（2）Compared with the diploid,the leaves of the autotetraploid plants had significantly different anatomical structure and stomatal features.The thickness of upper and lower epidermal cells cuticle,palisade tissue and sponge tissue,and the ratio of palisade tissue to sponge tissue increased by more than 20%,which difference was extremely significant.SR decreased by 11.38%,and the difference was significant.The size of the stomata increased,the density of the stomata decreased,the number of guard cells increased,and the number of chloroplasts in a single guard cell increased.In addition,the contents of chlorophyll a,chlorophyll b,chlorophyll a/b and total chlorophyll all increased significantly.（3）Compared with the diploid,the growth kinetics of the autotetraploid plants showed that during the first year,the growth was slow in March to June,and the plants were shorter,until in July the growth rate accelerated to exceed the diploid,which reached a significant level.（4）In the first year of planting,compared with the diploid,the inflorescence and single flowering duration of autotetraploid plants increased by 10.46%and 10.90%,respectively.The initial and full flowering periods were delayed,and the final flowering period was advanced,resulting in that the flowering duration was shortened by 19.08%（29d）.The single flower and inflorescence size increased by more than 14%,and the difference was extremely significant;the number of inflorescences per plant decreased significantly by 44.61%.The absolute values of petal redness（a^*）,yellowness（b^*）,and chroma（C^*）decrease,which meant that the degree of blue-violet was lower,and the color was lighter and brighter.The pollen was larger,but the vitality of pollen was extremely reduced by 35.01%.（5）Compared with the diploid,the maximum net photosynthetic rate of autotetraploid plants increased by more than 21%under the condition of light saturation or CO₂saturation,which meant stronger photosynthetic efficiency and efficiency of assimilating CO₂.（6）Autotetraploid plants had higher potential PSⅡactivity,stronger resistance to photoinhibition,and PSⅡresponse center had faster recovery ability after suffering reversible damage.The maximum PSⅡlight energy conversion efficiency（F_v/F_m）increased significantly,showing that it had certain advantages under dark adaptation conditions.The light saturation point increased by 10.17%and the compensation point decreased by 7.09%.The saturation intercellular CO₂concentration increased by 12.11%and the CO₂compensation point decreased by 15.62%.This showed that it had a wider adaptation range to light intensity and CO₂concentration.（7）Compared with the diploid,autotetraploid plants increased their semilethal temperature by 1.41℃in high temperature and 2.01℃in low temperature,indicating that they are more tolerant to both high and low temperature stress.（8）Compared with the diploid,the content of plumbagin in the aboveground and underground parts of the autotetraploid plants decreased by 51.74%and 10.63%,respectively,and the difference was significant.To sum up,the preliminary conclusion is that the autotetraploid Plumbago auriculata Lam.has increased photosynthetic characteristics,increased temperature tolerance,increased plant upright,enlarged flower organs,but reduced plumbagin.The potential for breeding value in ornamental is greater than that of medicinal.Therefore,autotetraploid Plumbago auriculata Lam.is expected to provide the market with a better uprightness and new varieties with larger flowers.It also provides a suitable plant material for global warming with its good heat resistance.