Abstract: As an important organ of absorbing water and nutrients for crops, root system architecture (RSA) has become a bottleneck in-depth study of crop roots due to the observing obstacles of soil. Three dimensional and visualization are important methods for studying and recognizing the morphological and structural traits of plants. In the aspect of crop root phenotype, these methods have a significance for characterizing the growth appearance of roots and for the influence of water, nutrients and other substances in the soil on RSA. In this paper, from the three dimensional perspective, the research progresses in detecting methods, three dimensional reconstruction and visualization of RSA in recent years were reviewed. Destructive and in situ detection methods of RSA were introduced. Destructive detecting methods mainly include (i) direct mining, (ii) protective soil block mining and cleaning, (iii) root scanning and image analysis, etc. These destructive methods have great advantages in obtaining global or local topology and extracting the plane geometric parameters. Meanwhile, in situ method mainly include six classes: (i) installation of root observation windows in field, (ii) ground penetrating radar, (iii) cultivation in controllable environment, (iv) CCD camera imaging, (v) 3D digitizing and (vi) X-ray computed tomography (CT), etc. These in situ methods retained the distribution information of RSA in space. However, most of the in situ detecting methods are only available for young or grown in controllable environment roots. Because a great deal of the detected data of RSA exist in the form of two-dimensional image, studies on extraction and analysis of plane geometry RSA parameters from two dimensional images were introduced as well, including root identification and parameter extraction algorithms and manual extraction software. Analysis showed that, the crop root data acquisition still exist some problems, such as time-consuming and laborious, redundant limitations, low integrity, difficult to integrate of each other, etc. Therefore, detecting and analyzing morphological traits of roots will still be the focus of RSA research. On the basis of RSA detecting technology, 3D modeling and visualization methods of RSA were reviewed on the aspects of 3D static modeling and dynamic growth simulation. 3D static modeling of RSA includes two kinds of methods: 3D modeling based on simulating algorithms and 3D reconstruction based on in situ detecting. Combining the computer simulation algorithms and understanding of RSA, the 3D modeling methods using simulating algorithms construct virtual roots with high morphological similarity of the real one. In contrast, 3D reconstruction based on in situ detection, which mainly includes XCT and 3D digital methods, could reflect the actual morphological structure of the RSA. Finally, the paper prospected the research on 3D reconstruction of crop roots under the condition of data missing. It was considered that 3D measurement and analysis of root topology could be realized using current technical means, while the 3D reconstruction of spatial distribution of RSA was difficult, especially in the premise of in situ measurement of crop roots in field. In addition, current 3D root data mainly have the data missing and low integration problems, so it is necessary to introduce the statistical methods like small sample theory and data fusion method into the research of 3D reconstruction of crop root to achieve a better reconstruction strategy by using multiple RSA data effectively in the premise of data missing.

Key words: crop, root system architecture, detecting method, 3D reconstruction, visualization