<em>In Vivo</em> Leaf Inoculation: An Alternative Method to Assess the Disease Resistance of Hybrid Clones in Poplar Breeding of Stem Canker Disease

Stem canker diseases caused by the pathogen Cytospora chrysosperma (Pers.) Fr.) and Botryosphaeria dothidea (Moug. ex Fr.) Ces. & de Not. are the two major forest diseases in the poplar plantations in China, sometimes which can destroy all the poplar seedlings or severely damage mature poplar forests. Hybrid breeding is the most direct and efficient method of controlling and managing tree diseases. However, assessing disease resistance or selecting disease-resistance clones based on In vitro stem inoculation is inefficient, time-consuming, and expensive, limiting the development of hybrid breeding of poplar stem canker disease. In this study, we proposed an alternative method to assess disease resistance to stem canker pathogens through in vivo leaf inoculation. The test materials used in this method can be on 1-year-old poplar saplings or the annual branches of perennial poplars in the greenhouse or the field. The critical step of this alternative method is the selection of inoculating leaves: the 5-7^th newly matured leaves might be the most suitable. The second critical step of the leaf inoculation method is to make wounds on plant leaves through needle pierces, providing sufficient lesions to measure disease severity. For the adequate number of leaves produced in the early stage of poplar breeding, this in vivo leaf inoculation contributes to the rapid, accurate, and large-scale screening of the disease-resistance poplar clones to stem canker pathogens. Moreover, this leaf inoculation method will also serve as an efficient method for screening pathotypes of stem canker disease pathogen C. chrysosperma, B.dothidea, or other poplar stem canker pathogens.