Morphological characteristics analysis and leaf area growth model construction of wrapper tobacco leaves under shading conditions based on image geometric information

【Objective】The key morphological characteristics of wrapper tobacco leaves under shading were screened， the area growth model of wrapper tobacco leaves was established，and the dynamic development regulation of wrapper to-bacco leaves under shading conditions was clarified，in order to provide theoretical reference for the precise cultivation of domestic wrapper tobacco leaves.【Method】The cigar variety CX81 was used as the experimental material，and three shading treatments were set up，which were light transmittance 60%（T1），light transmittance 70%（T2）and no shading with light transmittance 100%（CK）. Based on the image geometric information，the morphological characteristics of tobacco leaves were extracted，and the dynamic growth indexes of leaves at three leaf positions（upper，middle and lower positions） were determined. The morphological characteristics of tobacco leaves under different light transmittance were analyzed by partial least squares discriminant analysis（OPLS-DA），and the leaf area growth model was established.【Result】OPLS-DA results showed that there were obvious differences in the morphological characteristics parameters of upper，middle and lower tobacco leaves under different light transmittance treatments. With the increase of leaf position，the morphological indexes affected by shading gradually decreased. The common indexes of the three parts were leaf area growth rate，leaf area，leaf circumference and stem-leaf angle. Under shading conditions，the relationship between leaf area and shading time conformed to Richards model，and the equation was y=a/ （1+eb-cx）1/d. The model had good stability，high fitting degree and biological significance. With the increase of light transmittance，the leaf area increased first and then decreased，the leaf area of T2 treatment was the largest，and when shading for 45 d，the leaf area of T2 treatment increased by 4.7%-17.4% compared with CK. The average growth rate of tobacco leaves in the same position showed a slow-fast-slow change regulation，and the average growth rate of leaf area under T2 treatment was the highest， which was 5.5%-13.4% higher than that of CK.【Conclusion】The leaf area growth rate，leaf area，leaf circumference and stem-leaf angle are the key indexes affecting the leaf morphology of wrapper tobacco leaves under shading conditions. Richards model can effectively predict the area growth of wrapper tobacco leaves under shading conditions. 70% light transmittance can accelerate the growth rate of leaf area and effectively increase leaf area.