Coinfection in rice worsens diseases and compromises productivity, study finds

Research reveals that the interaction between viruses, fungi and bacteria intensifies symptoms in crops, highlighting the importance of defense genes in the rice immune response

06.09.2024 | 16:14 (UTC -3)
Cultivar Magazine

Plant co-infection, characterized by the presence of multiple pathogens in the same host, can both aggravate and mitigate the effects of diseases. A recent study investigated the impacts of this complex interaction on rice plants exposed to different pathogens. The research focused on pathogens from three groups: fungi, bacteria and viruses.

Coinfection between Rice necrosis mosaic virus (RNMV), the fungus magnaporthe oryzae (MO), responsible for brusone, and the bacteria Xanthomonas oryzae p.v. oryzae (XO), which causes leaf burn, was highlighted. The results show that simultaneous infections increase the growth of pathogens and the severity of lesions in plants, generating greater productivity losses.

Coinfection as an aggravating factor

The study demonstrated that co-infection of RNMV with other pathogens intensified symptoms in plants. The interaction between RNMV and rice blast (MO), for example, resulted in greater accumulation of the fungus and worsening of leaf lesions. This positive synergy was also observed in the interaction of RNMV with the bacterium leaf blight (XO) and with the cucumber mosaic virus (CMV), although the latter is only used in laboratory experiments. CMV, although not common in rice plantations, showed a similar behavior in co-infections, demonstrating that interactions between these pathogens are not restricted to the natural environment.

The research also investigated the role of the RNA silencing pathway in mediating these synergistic interactions. By analyzing rice mutants deficient in the RNA-dependent RNA polymerase 1 (OsRDR1) and 6 (OsRDR6) genes, the scientists observed the loss of positive synergy. This suggests that these genes play a key role in regulating plant immune responses to multiple infections.

Impacts on productivity and food security

Blast, caused by the fungus magnaporthe oryzae, and leaf burn, caused by bacteria Xanthomonas oryzae, are two of the main diseases affecting rice production worldwide. The losses caused by rice blast can reach 50% or more, depending on the growing conditions and the application of fungicides. In the case of leaf blight, the reduction in productivity can reach up to 80% in severe outbreaks. Co-infection with RNMV increases these impacts, making the plants more vulnerable and worsening the symptoms.

Rice, a staple food for more than half of the world’s population, is extremely susceptible to attacks by multiple pathogens. The combination of fungi, viruses and bacteria in the same host requires greater attention from scientists and farmers. Understanding these interactions is essential for developing more effective management strategies.

Full material on the study can be read at doi.org/10.1016/j.plantsci.2024.112244

Illustration of experimental procedures for RNMV infection: (A) Seedling preparation and inoculum. In vitro rice seed germination and soil preparation containing RNMV (PG) fungi; (B) 1st pathogen infection, RNMV transmission to Nipponbare, OsRDR1, and OsRDR6 mutants by growing seedlings in PG-infested soil for 20 days. Confirmation of RNMV infection in Nipponbare, OsRDR1, and OsRDR6 mutants using RT-qPCR and transfer to the new bucket with commercial soil; (C) 2nd pathogen co-infection, detached leaf assay performed to investigate co-infection of MO, XO and CMV pathogens, analysis of disease symptom development (lesion sizes) and quantification of fungal and bacterial biomass, and the effect of the interaction of RNMV and the second pathogen (MO, XO and CMV) within the host on RNMV accumulation in the mutant lines Nipponbare, OsRDR1 and OsRDR6 was evaluated by RT-qPCR analysis
Illustration of experimental procedures for RNMV infection: (A) seedling preparation and inoculum. In vitro rice seed germination and soil preparation containing RNMV fungi Polymyxa graminis (PG); (B) 1st pathogen infection, RNMV transmission to Nipponbare, OsRDR1 and OsRDR6 mutants by growing seedlings in PG-infested soil for 20 days. Confirmation of RNMV infection in Nipponbare, OsRDR1 and OsRDR6 mutants using RT-qPCR and transfer to the new bucket with commercial soil; (C) co-infection of 2nd pathogen, detached leaf assay performed to investigate co-infection of MO, XO and CMV pathogens, analysis of disease symptom development (lesion sizes) and quantification of fungal and bacterial biomass, and the effect of the interaction of RNMV and the second pathogen (MO, XO and CMV) within the host on the accumulation of RNMV in the mutant lines Nipponbare, OsRDR1 and OsRDR6 was evaluated by RT-qPCR analysis

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