Molecular Pathogens, 2025, Vol.16, No.3, 121-133 http://microbescipublisher.com/index.php/mp 126 preceded by a specific part of the host or consumed key nutrients, the post-invasion pathogen may be suppressed by “no place to gain a foothold” or lack of required resources. For example, on the leaves of rapeseed seedlings, early infection of the black spot bacteria takes up most of the leaf space and triggers local necrosis, which may hinder the subsequent germination and invasion of the Leptosphaeria maculans spores flying in the leaves. Therefore, the attenuated virus disease that occurs first suppresses the strong virus disease that occurs later to a certain extent. Recent studies provide direct evidence: Alternaria brassicae pre-inoculated can induce defense responses of plants, thereby reducing the success rate of infection of subsequent inoculation of pelvic bacteria (Leptosphaeria maculans pathogen). This experimental results show that plant defense activated by the initial infectious pathogen has a cross-protective effect on the second pathogen within a certain time window, manifested as a decrease in the latter's pathogenicity (Qayyum et al., 2025). In this study, the researchers speculated that resistance induced by the black spot bacteria may be related to elevated plant secondary metabolites (Leptosphaeria maculans). When the two pathogens coinfect, the metabolites of one of the parties are inadvertently toxic to the other party and are also an antagonistic form. It is worth noting that plants sometimes "leverage" antagonism to protect themselves: some studies have found that in certain dual infection situations, hosts will promote the expansion of pathogens that are less harmful to themselves, thereby inhibiting the reproduction of more destructive pathogens, which is an interesting strategy for plants to adapt to resist multiple diseases. 4.3 The impact of composite infection on epidemics and prevention Multi-pathogen composite infection has a profound impact on the epidemic course and prevention and control strategies of rapeseed diseases. Under compound infestation conditions, the total disease burden borne by the plant is often higher than that of a single disease situation. This includes both the superposition of yield loss and the changes in the rate of disease prevalence. When synergistic effects dominate, multiple infections may lead to earlier outbreaks of diseases and a steep epidemic curve, posing challenges to gaining time in field prevention and control (Neik et al., 2020). Even if there is an antagonistic effect, one pathogen is suppressed and the other pathogen may still spread widely, and the final level of harm to the plant may not be reduced. Therefore, on a field scale, composite infection usually means more complex and difficult to control the flow dynamics. Secondly, compound infection raises difficulties in the prediction and early warning of routine diseases. Traditional prediction models based on meteorological and historical data mostly target a single disease, and when multiple diseases intertwined, the single disease model may be inaccurate. This requires the development of a more comprehensive disease prediction model that takes into account the main pathogen synergistic/antagonistic effects to improve forecasting accuracy in multi-disease settings (Daval et al., 2020). Third, compound infection has a huge impact on prevention and control decisions. On the one hand, the coexistence of multiple diseases limits the effectiveness of a single prevention and control measure. For example, spraying agents targeting one pathogen may not prevent and control another disease, and may even indirectly contribute to the main disease by inhibiting antagonistic pathogen. On the other hand, there may be conflicts or compatibility issues in the prevention and control measures of different diseases and require overall arrangements (Qayyum et al., 2025). From the perspective of breeding, the existence of compound diseases puts forward higher requirements for disease breeding. In the past, breeding focused on the introduction of single disease resistance genes, but in reality, new varieties may have to face multiple challenges such as Sclerotinia sclerotiorum, Leptosphaeria maculans, and viral diseases at the same time. If you only choose for resistance to a certain disease, you may lose sight of one thing. Therefore, it is now proposed that attention should be paid to cultivating multi-resistant or broad-spectrum disease-resistant varieties, and the combined infection pressure should be included in the breeding evaluation system. 5 Factors That Affect the Occurrence of Disease Symbiosis 5.1 Environmental and climate factors Environmental conditions, especially climatic factors, play a decisive role in the symbiosis of rapeseed diseases. Factors such as temperature, humidity and rainfall not only affect the prevalence intensity of a single disease, but
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