Molecular Pathogens, 2025, Vol.16, No.3, 121-133 http://microbescipublisher.com/index.php/mp 128 5.3 Host resistance and pathogen evolution factors The disease resistance level of the host plant itself and the evolutionary dynamics of the pathogenic bacteria are also important factors that affect the occurrence of disease symbiosis. Variety resistance directly determines whether the plant can resist the invasion of multiple pathogens at the same time. If the rapeseed varieties are not resistant to the main diseases, a "comprehensive susceptibility" may occur in the fields. Once the environment is suitable, multiple diseases will go straight in and cause disasters. In this variety, as long as the climate matches, these types of diseases often occur at the same time. If the variety carries resistance genes for certain diseases, the disease symbiosis pattern can be significantly changed. For example, the anti-Leptosphaeria maculans variety promoted in Canada has greatly reduced the proportion of Leptosphaeria maculans in compound diseases, and other diseases such as white frost disease may be relatively prominent (Hasan and Rahman, 2016). It can be seen that variety resistance will "reshape" the field disease spectrum: varieties that resist a certain disease will selectively inhibit the occurrence frequency of the disease in the field, thereby changing the structure of coexistence of multiple diseases. Secondly, the evolution of pathogenic bacteria will also affect symbiosis. On the one hand, the emergence of new high-virulence strains or physiological species may break through breed resistance, make the originally controlled disease popular again, and form a new combination with other diseases. On the other hand, community structure changes may also occur between different pathogenic species through competition and adaptation. Latest research shows that gene flow may even occur between pathogenic bacteria. Some pathogens have increased virility after obtaining exogenous genes, and are more likely to win under co-infection conditions (Figure 2) (Qayyum et al., 2025). This kind of evolution will profoundly affect the future symbiotic pattern of disease. Figure 2 Schematic diagram of the potential signalling and regulatory gene network during the R-Avr interaction in Brassica napus–Leptosphaeria. maculans pathosystem producing a hypersensitive response. The arrows indicate the pathways and the regulatory factors activated during the immune response. Abbreviations: CAZys, Carbohydrate active enzymes; CWDEs, Cell wall-degrading enzymes; PL, Pectin lyases; SA, Salicylic acid; JA, Jasmonic acid; ET, Ethylene; ICS1, Isochorismate synthase 1 (Adopted from Qayyum et al., 2025) 6 Comprehensive Prevention and Treatment in The Context of Multiple Diseases of Rapeseed 6.1 Breeding and application of anti-multiple disease varieties Cultivating and planting rapeseed varieties that are resistant to multiple diseases is one of the fundamental ways to prevent and control the occurrence of complex diseases in the field. Traditional breeding mostly focuses on improving resistance to a single disease, and in the face of the coexistence of multiple diseases, new varieties need to have broad-spectrum resistance to major pathogens. In recent years, with the deepening of plant diseases
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