Fertilization with beneficial microorganisms decreases tomato defenses against insect pests

The 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

Fertilization with beneficial microorganisms decreases tomato defenses against insect pests

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

Effective Microorganisms (EM®) is a "biofertiliser” soil inoculant, marketed as a crop yield enhancer. However, the literature has neither comprehensively reviewed its purported effects on harvests across multiple species nor investigated its effects on plant herbivore defence other than this group's previous research on tomatoes. Here a meta-analysis of 39 journal articles and a greenhouse experiment with nine crop species afforded a nuanced assessment of Effective Microorganisms' effects on plant growth and yield. Overall, in line with predictions, Effective Microorganisms showed significant positive effect on yield and growth (0.03 effect sizes increase) in the meta-analysis, and increased growth 16% in the greenhouse, but with strong, and at times negative, species-specific responses. An additional potential benefit of Effective Microorganisms includes increased defence against herbivore attack, but inoculated corn (Zea mays) in a field and a greenhouse experiment exhibited decreased defences. Specifically, the field experiment demonstrated that Effective Microorganisms treatment corresponded to a 26% reduction in predatory insect diversity on corn plants, while not improving growth or yield but did increase water uptake. A subsequent greenhouse experiment suggested likely physiological mechanisms behind the loss of predator diversity. When non-inoculated control corn plants were set upon by caterpillars of the herbivorous insect Spodoptera littoralis, the plants increased production of defensive volatile organic compounds (VOCs) by 272%. Surprisingly, inoculation with Effective Microorganisms rendered greenhouse corn plants 51% more palatable to S. littoralis. Further localised studies are, therefore, needed to efficiently incorporate Effective Microorganisms with either conventional or sustainable agricultural management systems