Fertilization with beneficial microorganisms decreases tomato defenses against insect pests

Abstract

International audienceThe adverse effects of chemical fertilizers on agricultural fields and the environment are compelling society to move toward more sustainable farming techniques. “Effective microorganisms” is a beneficial microbial mixture that has been developed to improve soil quality and crop yield while simultaneously dramatically reducing organic chemical application. Additional indirect benefits of beneficial microorganisms application may include increased plant resistance to herbivore attack, though this has never been tested till now. Tomato plants were grown in controlled greenhouse conditions in a full-factorial design with beneficial microorganisms inoculation and commercial chemical fertilizer application as main factors. We measured plant yield and growth parameters, as well as resistance against the generalist pest Spodoptera littoralis moth larval attack. Additionally, we measured plant defensive chemistry to underpin resistance mechanisms. Overall, we found that, comparable to chemical fertilizer, beneficial microorganisms increased plant growth fruit production by 35 and 61 %, respectively. Contrary to expectations, plants inoculated with beneficial microorganisms sustained 25 % higher insect survival and larvae were in average 41 % heavier than on unfertilized plants. We explain these results by showing that beneficial microorganism-inoculated plants were impaired in the induction of the toxic glycoalkaloid molecule tomatine and the defense-related phytohormone jasmonic acid after herbivore attack. For the first time, we therefore show that biofertilizer application might endure unintended, pest-mediated negative effects, and we thus suggest that biofertilizer companies should incorporate protection attributes in their studies prior to commercialization

Soil microbial inoculation increases corn yield and insect attack

“…4b). We found similar results with tomatoes in a separate study, in which Effective Microorganisms soil application interfered with plant signalling pathways that trigger upregulation of inducible defences after herbivore attack (Megali et al 2014). This inhibition of innate plant defences renders Effective Microorganisms not only ineffective as a means of pest management, but could also potentially endanger efforts in safeguarding the harvest against herbivory.…”

“…Pineda et al (2010) has highlighted the importance of microbial-mediated positive effects on induction of both direct and indirect plant defences. And while previous research found that Effective Microorganisms reduced defence and resistance in tomatoes (Megali et al 2014), Effective Micoorganisms' effects on other traits (such as growth and yield) appear to be highly species-specific (see for instance the meta-analysis presented here). We therefore hypothesise this specificity may hold true for traits associated with plant defence as well.…”

“…Indeed, it is difficult to separate the effects of the Bokashi organic substrate and beneficial microorganisms in the inoculant for Effective Microorganisms treatment on plant performance (Megali et al 2014). Mayer et al (2010) demonstrated that the mineral and carbon resources in Bokashi alone are sufficient to increase crop yield, while beneficial microorganism application by itself had no measurable impact on yield for crop species in their investigations.…”

“…In addition, these studies and others have not assessed Effective Microorganisms' potential for enhancing or reducing plant defence and resistance against herbivore pests. To our knowledge, only one recent paper has shown that Effective Microorganisms inoculation of tomato plants not only promotes increased yield but also increases susceptibility to Spodoptera littoralis caterpillars via inhibition of chemical defence production (Megali et al 2014).…”

Exploiting of honey-associated Bacillus strains as plant-growth promoting bacteria for enhancing barley growth in rare earth tailings

“…They are widely used in improving efficiency of phytoremediation or enhancing plant growth (Qin et al 2014;Sarma and Saikia 2014). However, in the past, there were few attempts to employ bacteria isolated from the nonrhizosphere for improving plant growth (Megali et al 2014). Recently, many honey-associated Bacillus strains have been exploited for producing an antibiotic substance to improve plant resistance to diseases (Esawy et al 2011;Zhao et al 2013).…”