Arbuscular mycorrhiza protects soybean plants against Macrophomina phaseolina even under nitrogen fertilization

Abstract

The capacity of arbuscular mycorrhizal fungi (AMF) to alleviate the negative effects incited by root pathogens in a range of plant hosts has been established. On the other hand, accumulated evidence also shows that fertilization practices can negatively impact AMF. Nevertheless, the interaction between AMF, pathogens and fertilizers, especially nitrogen (N) fertilizers, has not been previously reported. In this work, the effect of nitrogen on both the severity of the pathogen Macrophomina phaseolina (charcoal root rot) and the protection by the arbuscular mycorrhiza fungi (AMF) Rhizophagus intraradices was investigated in greenhouse experiments using soybean (Glycine max) as a host. The treatments were two levels of N (0 and 92 kg of urea ha −1 ), inoculation and non-inoculation with the AMF, and infection and non-infection with the pathogen. Soybean was harvested at R4 phenological stage (completed pod formation). Plant biomass, numbers of pods and leaves, plant height, root length, greenness index, mycorrhizal colonization and disease severity were measured. Pathogen infection reduced soybean biomass and negatively affected the greenness index, but co-inoculation with AMF improved these parameters. Nitrogen fertilization reduced AMF colonization but not arbuscules percentage. N fertilization increased disease severity but mycorrhizal symbiosis was able to reduce it. These results demonstrate that severity of charcoal root-rot disease in N fertilized soybean can be reduced by AMF inoculation. The implication of these results is that N fertilization could increase the risk of diseases in soybean but mycorrhiza could contribute to soybean charcoal root rot control even if the crop is under N fertilization.

Effect of Root Colonization by Arbuscular Mycorrhizal Fungi on Growth, Productivity and Blast Resistance in Rice

“…In other studies, different levels of Glomus versiforme colonization were observed in sorghum genotypes which conferred either beneficial or detrimental effects to the host plant, regardless of the level of root colonization (Grace et al 2009). Several pieces of evidence support that root colonization by AM fungi confers disease resistance in several plant species, but most of these studies focused on resistance to root pathogens (Azcón-Aguilar and Barea 1997; Sikes et al 2009;Jacott et al 2017;Spagnoletti et al 2020). Different results are found in the literature on the impact of the AM symbiosis on foliar pathogens which might well depend on the identity of the AM fungus, the host plant, and the interacting organism (Fritz et al 2006;Pozo and Azcón-Aguilar 2007;Jung et al 2012;Pozo et al 2013;Jacott et al 2017).…”

Macrophomina phaseolina: General Characteristics of Pathogenicity and Methods of Control

“…Finally, fertilization has shown different effects on the severity of M. phaseolina. Phosphorus fertilization have shown a reduction, while nitrogen increased disease severity (Spagnoletti et al, 2018(Spagnoletti et al, , 2020.…”

“…Although mycorrhizal symbiosis is not able to avoid infection M. phaseolina or any other pathogens, a reduction in root infection by M. phaseolina and disease symptoms severity have been reported (Doley and Jite, 2013;Oyewole et al, 2017;Spagnoletti et al, 2017Spagnoletti et al, , 2020Marquez et al, 2018). These observations were associated with a decreased oxidative damage and the boosting of defense response mechanisms, including a significant increase in total phenol and proline contents, and superoxidase activity (Doley and Jite, 2013;Spagnoletti et al, 2017).…”

“…Eventually, even though phosphorus fertilization have shown a reduced disease severity of M. phaseolina, a partial reduction of the AMF protection was observed when both combined treatments where applied (Spagnoletti et al, 2018). Conversely, AMF protects soybean plants against M. phaseolina even under nitrogen fertilization (Spagnoletti et al, 2020). Hence, its important to consider the effect of integrated management in agricultural practices.…”

Roles of Arbuscular Mycorrhizal Fungi on Plant Growth and Performance: Importance in Biotic and Abiotic Stressed Regulation

“…Numerous studies have proven that AMF reduces the damage caused by various plant pathogens [144][145][146] (Table 6). For example, studies carried out by [147] demonstrate that the severity of charcoal root-rot disease in soybean can be reduced by AMF inoculation. In the presence of Fusarium, arbuscular colonization increased shoot dry weight [144].…”