Culture And Identification Of Chlorella Sp. And Its Effects On The Leaf Photosynthesis In Torreya Grandis 'Merrillii'

Torreya grandis‘Merrillii'is a peculiar and rare Chinese economic tree species.It integrates fruit,oil and medicinal use with very high economic value.In recent years,with the development of T.grandis‘Merrillii'industry,the incidence of Chlorella sp.on T.grandis‘Merrillii'is getting higher and higher,which has seriously affected the growth of T.grandis‘Merrillii'and caused huge economic losses to the farmers.However,the research on the Chlorella sp.is still in its infancy,the mechanism of its damage is not yet clear,and the types of pathogen microbes are still inconclusive.In this paper,the annual leaves of 10-year-old grafted T.grandis‘Merrillii'seedlings infected by Chlorella sp.in different degrees under natural conditions were used as experimental objects.To explore the effects of Chlorella sp.on photosynthesis and growth of T.grandis‘Merrillii'leaves,the physiological and biochemical indexes such as photosynthetic rate,specific leaf weight,chlorophyll and nitrogen concentration were measured.The species and types of Chlorella sp.on T.grandis‘Merrillii'.from three different places were further identified by morphological and living habits observation and molecular biological techniques such as 18S rDNA and ITS gene sequence analysis.Meanwhile,to explore more effective prevention methods six control agents commonly used in the field were used to control Chlorella sp.in the laboratory,which provide theoretical basis for comprehensive control of Chlorella sp.on T.grandis‘Merrillii'.The results of this study are as follows:1.With the increase of infection degree of Chlorella sp.,photosynthetic rate,chlorophyll concentration,nitrogen concentration,water content,specific leaf mass,and number of leaflet of T.grandis‘Merrillii'leaves showed a downward trend,and curvature of leaflet showed an upward trend.However,the photosynthetic rate,chlorophyll concentration and nitrogen concentration of uninfected leaves of infected T.grandis‘Merrillii'trees were significantly higher than that of control leaves.2.According to the results of morphological identification,the A-type Chlorella sp.was similar to the morphology of Chlorella ellipsoidea which is a cause of green algae disease in tomato,the B-type Chlorella sp.was similar to the morphology of Ulothrix sp.which could lead to green algae disease in cucumber.However,the response of Chlorella sp.to pH was similar to that of Scenedesmus obliquus.The sequence alignment showed that the 18S rDNA and ITS gene sequences of the two forms of Chlorella sp.also had a high homology with Asterarcys quadricellulare of the Scenedesmaceae family with the similarity rate being 100%.3.Chlorella sp.is resist to strong alkali and shade.It grows well in the environment with pH value of 9.0 to 10.0.Moderate shading is beneficial to the growth of Chlorella sp.in heterotrophic environment.Lime sulphur,CuSO₄·5H₂O,quicklime and soap powder can effectively control Chlorella sp.on T.grandis‘Merrillii',the control rate can reach 89.80%,98.86%,91.44%and 97.27%,respectively.This study analysis the pathogens and hazards of Chlorella sp.,providing a theoretical basis for future scientific researchers to understand the Chlorella sp.on T.grandis‘Merrillii'.Comparing the effects of different anti-green-algae medicines on Chlorella sp.,providing an important guarantee for the healthy development of T.grandis‘Merrillii'industry.