Coinfection in rice worsens diseases and compromises productivity, study finds

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