In Situ Root Observation System Designing And Root Research For Plants In Greenhouse

Root is the principal part of plant to absorb water and nutrient,anchor root system,and affect yield and quality.Real-time aciquisition of root architecture parameter is necessary to phenomics research,plant nutrition research and physiological ecology.Non-destructive detection of root system architecture is difficult to perform due to the hidden nature of the root in soil.In this study,a micro root observation named microrhizotron was designed.It could be installed around root system in situ for a long time and monitor growth of roots.It was applied to nondestructive observation on roots,and analysis dynamic changes of root development in response to salt stress and root nematode infection.The research was detailed below.(1)Designing a kind of nondestructive micro root observation and processing system(microrhizotron).The microrhizotron consisted of a micro camera,an optical amplifier,LED,a power supply and wireless module integrated in the camera,and image processing part.The size of the micro camera was 1.1 cm × 1.1 cm × 1.2 cm.The co llected root image was transmitted to the terminal receiving device through the WIFI signal formed by the wireless control module.(2)An Inception-Unet method was proposed to enable root image segmentation.The encoder-decoder architecture and skip connection in Unet helped to combine low-level features of roots with high-level features.Adding GoogLenet Inception in Unet will strengthen root traits of different size,and also increase width of the architecture.The proposed method was trained,validated and tested with root images from in situ observation with microrhizotron.Root axes and root hairs were separated,and then root parameters were extracted.The result showed that Inception-Unet significantly outperformed the previous algorithms on the accuracy(0.972).(3)Maesuring root system architecture with digitalizer,and obtaining the optimal preset position and pattern of microrhizotron.In order to figure out root system architecture traits and provide scientific evidence for microrhizotron installation,the spatial structure after root elongation was analyzed in circumferential direction,radial direction,and vertical direction.The results showed that for pepper,such as lateral roots initiated from two opposite poles of protoxylem pole pericycle cell,most lateral roots were constrained to 45°in horizontal direction to root initial position after elongation.According to the analysis of root initiate principle and root elongation discussed before,8 installation patterns for pepper root and 4 installation patterns for tomato root were tested and verified to determine high probability of root interception.The result showed that,for pepper,if installation of microrhizotron were at random,interception probability might be only 73.5%,while presetting pattern horizontal angle 45°+radius 30 mm+vertical angle 45°according to root architecture features increase this value to 96.7%.(4)In situ observation for pepper root under Ca(NO3)2 stress.The adding of Ca(NO3)2 causes changes in root hairs.There was little difference in root hair length between low concentration stress and the control group.Root hair was rare or almost absent under the conditions of 100mmol/L and 150mmol/L Ca(NO3)2.Root hair began to decrease under conditions of 100mmol/L salt stress since DAT 25,and root hair reduction under the conditions of 150mmol/L was observed salt stress since DAT 10.Through the observation of microrhizotron,it was found that root system was affected by higher concentration of Ca(NO3)2 stress earlier than the shoot part,and the change of root hair length was slightly earlier than the change of root system architecture.(5)In situ observation for tomato root development infected with Meloidogyne incognita.The result showed that root began to swell since 25 days after infection.Compared with CKs,diameter of root-knot showed a dramatic increase since 30 days after infection,and it could reach a very high value,about 3-5 times than that in CK groups.Root hair length in swelling parts was observed elongation in 20 days.The defense mechanism was not only limited to rootknot part,but also to Noknot parts in the nematodes inoculation plants.The effect seemed to spread since DAI 25,and root hair elongation gradually increased from near to far along the root knot.In DAI 35,2 mm far from root-knot and 4 mm far from root-knot all produced root hairs more than 1.4 mm,while root hairs in CK groups didn’t exceed 0.6 mm,indicating defense mechanism to nematodes infection a wide range of influence and response.