Physiological And Spectral Changes Of Pinus Elliottii After Artificial Inoculation With Pine Wood Nematode

Bursaphelenchus xylophilus(Steiner & Buhrer)Nicher can kill pine trees in a short time and seriously threaten the health of pine forests.The disease caused by Bursaphelenchus xylophilus is the most serious disease of pine forests in China.Since the invasion of pine wood nematode was first found in Nanjing lodgepole pine in1992,the disease of pine wood nematode has seriously affected the native pine species such as Pinus thunbergia,Pinus massoniana,Pinus yunnanensis,Pinus tabulaeformis,Pinus sylvestris var.mongolica,Pinus koraiensis in China.Pinus elliottii,native to North America,has been introduced and cultivated in most areas of southern China and has important economic and ecological value.Previous studies showed that Pinus elliottii had high resistance to pine wood nematode disease.However,in 2008,a large number of dead trees of Pinus elliottii infected with pine wood nematode disease were found in Fujian Province for the first time,questioning this conclusion.In this paper,under the condition of artificial inoculation of pine wood nematodes,the variation rules of disease susceptibility characteristics,physiological indicators,and hyperspectral characteristics of Pinus elliottii under different time of disease were clarified.The main research results are as follows:1.Based on the changes in the appearance of Pinus elliottii infected with pine wood nematodes,the pathological characteristics of pine wood nematodes were determined as follows: discoloration starts from the base of needle leaves,and the color of needle leaves first changes from dark green to pale color,and then changes to brick red.2.The basic change characteristics of nematode quantity and physiological indexes of Pinus elliottii infected with pine wood nematode were determined,including water content,chlorophyll content,carotenoid content and malondialdehyde content.The general change trend of physiological indexes of Pinus elliottii was consistent with that of Pinus massoniana.The results showed that the amount of nematode in pine wood increased after the invasion.In the early stage of the disease,the growth rate of the pine nematode population increased continuously,and in the middle stage,the growth rate gradually decreased,and in the late stage of the disease,the pine nematode population remained stable.During the disease,water content has been decreasing.Chlorophyll and carotenoid contents increased slightly at first,then decreased continuously until the host died.Malondialdehyde content increased in the early stage of the course of disease and decreased rapidly in the middle stage.3.The spectral curve variation characteristics of Pinus elliottii disease were clarified.With the development of the disease,the peak value of the spectral reflectance of green light band(490nm-560nm)decreased gradually.The absorption valley of the spectral curve of red light(620nm-700nm)rises gradually until it disappears.In the near infrared band(760nm-800nm),the spectral reflectance decreases,and the spectral curve slope decreases in the red edge range(680nm-760nm),resulting in the phenomenon of "blue shift" of the red edge.4.Linear model,nonlinear model and stepwise regression model were constructed by combining physiological and biochemical indexes and spectral characteristic parameters of susceptible Pinus elliottii.By testing the accuracy of the model,the following conclusions were obtained: When using the same spectral characteristic parameters,the determination coefficient(R-square)and model accuracy(RSME)of the estimation model of carotenoid content in conifers were better than other physiological indexes.By establishing and testing different spectral characteristic parameter models of the same physiological index,the optimal singlefactor model for estimating the moisture content of susceptible Pinus elliottii needles was the quadratic polynomial model constructed by PRI,and the optimal single-factor model for estimating the chlorophyll content of susceptible Pinus elliottii needles was the quadratic polynomial model constructed by MSI.The optimal single factor model for estimating the carotenoids of pine needles in susceptible wetlands was the quadratic polynomial model constructed by Ratio975.In the multiple stepwise regression model,PRI and PSSRb had the best estimation effect on water content of affected Pinus elliottii,GVWI had the best estimation effect on chlorophyll content of affected Pinus elliottii,and Ratio975 and WI had the best estimation effect on carotenoid content of affected Pinus elliottii.In conclusion,the present study clarified the pathological features of Pinus elliottii after artificial inoculation with pine wood nematode,revealed the spectral variation characteristics of Pinus elliottii,and selected the optimal single-factor estimation model and stepwise regression model combined with the changes of host physiological indicators,providing scientific basis and support for the subsequent airborne(space-borne)remote sensing monitoring technology research.