Molecular Soil Biology 2025, Vol.16, No.2, 73-82 http://bioscipublisher.com/index.php/msb 76 4 Screening of Disease Resistance Germplasm Resources 4.1 Collection and evaluation of germplasm resources The first step in screening disease resistant germplasm of Leonurus japonicus var. hunanensis is to collect germplasm resources from different ecological regions. Identify its main growth areas in China, and analyze its habitat characteristics and environmental adaptability. These areas include areas with different climatic conditions and disease pressures, so as to ensure the diversity of collected resources and help understand its population dynamics and migration patterns (Figure 2) (Wang et al., 2023b). Germplasm samples were collected from natural populations, cultivation sites and off-season experimental fields to comprehensively capture their genetic variability. Figure 2 Geographical map of the distribution point of Leonurus japonicus (Adopted from Wang et al., 2023b) The preliminary evaluation mainly focused on phenotypic traits, including growth rate, plant vigor and apparent resistance to powdery mildew, gray mold and leaf spot. In addition, the genetic characteristics of the collected germplasm were analyzed by molecular markers to determine the variability of the collected germplasm. The combination of phenotypic data and genetic data enables researchers to select potential Germplasms for further evaluation (Sun et al., 2022). 4.2 Evaluation method of disease resistance The field experiment was used to analyze the difference of disease resistance of germplasm under natural conditions. These tests were conducted in areas with high disease incidence to ensure that plants were exposed to the pressure of natural diseases. The disease resistance performance was determined by evaluating the incidence and severity of powdery mildew and leaf spot disease. In order to achieve more accurate evaluation, artificial inoculation technology is also used. The pathogen (such as powdery mildew pathogen Podosphaera xanthii, Botrytis cinerea, Cercospora spp.) was inoculated on the germplasm samples. This method can directly compare the disease resistance under standardized conditions. Germplasms with low susceptibility were selected for further study (Liang et al., 2018). The disease resistance was quantified by incidence, disease index (DI) and disease resistance coefficient. The disease index is calculated according to the severity of plant population symptoms, and the disease resistance
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