Medicinal Plant Research 2024, Vol.14, No.6, 345-357 http://hortherbpublisher.com/index.php/mpr 348 Figure 1 Representative pictures for aphid settlement at 3 d, 7 d and 10 d after aphid inoculation on selfrooted grafted chrysanthemum (Cm / Cm) and the graftedArtermisia-chrysanthemum (Cm / As) (Adopted from Wang et al., 2024) Image caption: The figure shows the comparison of aphid colonization on leaves of self-rooted chrysanthemum (Cm/Cm) and chrysanthemum grafted on Artermisia (Cm/As) at 3, 7, and 10 days after aphid inoculation. The results show that over time, the number of aphids on Cm/Cm plants increased significantly, while the aphid expansion on Cm/As plants was limited and showed a slow growth trend (Adapted from Wang et al., 2024) In terms of biochemical markers, flavonoid and phenolic acid content, antioxidant enzyme activity, and secondary metabolite composition can serve as important resistance response indicators when attacked by pests and diseases (Gong et al., 2019; Lu et al., 2024; Wang et al., 2024). Molecular resistance indicators include the expression of defense-related genes (e.g., WRKY, bHLH, NPR1, CmWD40), differentially expressed genes (DEGs) identified in transcriptome analysis, and resistance-related alleles detected by SSR, ISSR or SNP markers (Guo et al., 2014; Zhang et al., 2019; Ding et al., 2023; Miao et al., 2023a;b; Li et al., 2024a). The application of these markers not only helps early screening, but also accelerates the breeding process of resistant varieties. 4 Methods for Screening Disease and Pest Resistant Varieties 4.1 Field-based evaluation under natural infection Field evaluation is still one of the core methods for screening disease and insect resistance of Chrysanthemum morifolium. Multi-location trials usually plant candidate varieties in different ecological and environmental regions to expose their true performance under diverse pathogens and pests. This method can capture the interaction effect between genotype and environment, thereby screening out resistant varieties with stable performance under different climatic conditions and pathogen groups. For example, a large-scale field trial conducted by Sidhya et al. (2024) on 40 Chrysanthemumgenotypes showed that there were large differences in the degree of infestation of aphids, mealybugs and mites among different varieties, and it was mainly due to genetic differences. Similarly, resistance to white rust and leaf blight is often verified through cross-regional and cross-season field evaluations to ensure that the selected varieties have broad-spectrum and stable resistance (Sumitomo et al., 2021; Seliem et al., 2024). To be closer to the challenges in actual planting environments, resistance screening is often combined with other environmental stresses such as drought, salinity or poor soil. This helps to identify varieties with multiple stress resistance, as environmental stress often affects the susceptibility of plants to diseases and insects. Studies have found that under combined stress conditions, some anatomical traits (like cuticle thickness and stem thickness) and the physiological responses of plants are closely related to their enhanced resistance to diseases such as bacterial blight (Li et al., 2024b; Seliem et al., 2024).
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