Excessive inorganic fertilizers applied to pineapple crops in Mexico cause the progressive degradation and pollution of soils in the short- and long-term, and they also increase production costs. An alternative to reduce excessive fertilization is its partial substitution by nutrition and growth enhancing arbuscular mycorrhizal fungi (AMF). The goal of this research was to compare the effect of AMF inoculation combined with different fertilizer doses and full chemical fertilization on pineapple yield variables in a commercial plantation. We used a randomized block design with six treatments: a non-inoculated control with 100% chemical fertilization, and five treatments with AMF inoculation and fertilization doses of 0%, 25%, 50%, 75%, and 100% chemical fertilization. There were four replicates of each treatment containing 30 plants in each experimental unit (plot). We measured the dry weight of the D-leaf 9 months after planting, and the root mycorrhizal colonization percentage, yield, and fruit quality after 18 months. Mycorrhizal inoculation equated to 100% chemical fertilization already when combined with 25% fertilization and surpassed it when combined with 50% fertilization in most of the yield variables measured. The fruit mass and organoleptic variables were significantly higher in mycorrhizal plants with 50% fertilization than in the non-inoculated control and the treatments inoculated with AMF and combined with 0%, 25%, 75%, and 100% of a dose of chemical fertilizer. Inoculation with mycorrhizal fungi in the field could reduce chemical fertilizer application by 50%, with no yield loss and with improved fruit quality.

Biocontrol traits of arbuscular mycorrhizal fungi (AMF), in terms of single and mixed species inoculum, against the root knot nematode Meloidogyne incongita in Impatiens balsamina L., were examined with and without mineral fertilization in a greenhouse pot experiment. At harvest, 60 days after sowing, general plant growth parameters and plant defense response in terms of antioxidant activity and content of phenolic compounds in roots and leaves were measured. Also AMF root colonization and abundance ofnematode root-knots were determined. Mineral fertilization increased all plant growth parameters measured, which coincided with an increased disease development caused by M. incognita. Inoculation with AMF mitigated the observed plant growth reduction caused by M.incognita, though, higher abundance of M. incognita root knots was found in mycorrhizal plants. Plant defense responses in terms of antioxidant activity and content of phenolic compounds did not seem to be linked to the observed biocontrol traits of AMF against M. incognita. However, roots inoculated with a consortium of AMF, which presented less nematode root knots than roots with the single species inoculum, had the highest level of phenolic compounds. The results from the present study suggest that AMF induce tolerance in I. balsamina against the root knot nematode M. incognita.

<![CDATA[Plants stressed by pathogens activate a variety of defense mechanisms to survive. The osmoprotector amino acids, including proline, are among these defense mechanisms. In this work, the effects of arbuscular mycorrhizal fungi on plants infested by root-knot nematodes were evaluated with regard to the accumulation of the osmoprotectant proline. A 2x3 factorial design was established with 8 treatments -with and without nematodes, with and without mycorrhizae, and with and without fertilizer application - with 4 replicates. Two weeks after inoculation with arbuscular mycorrhizal fungi, the plants were infested with 4 nematode egg masses, and 8 weeks later, the plants were harvested. The inoculation with the arbuscular mycorrhizal fungi significantly reduced the proline content, with the non-inoculated plants exhibiting a higher concentration. Neither the infestation of the nematodes nor the addition of fertilizer significantly affected the proline content. Plant height, stem diameter, leaf area, number of leaves, and fresh weight were significantly improved by the presence of the arbuscular mycorrhizal fungi. The interaction of the fungi and the fertilizer did have a significant effect for height and leaf area. The nematode infestation and the fertilization did not affect mycorrhizal colonization.]]>

A strategy to increase the productivity of pineapple agricultural systems is the excessive application of chemical fertilizers. In the state of Veracruz, Mexico, pineapple fields are being fertilized with P (180 to 240 kg ha-1) to maximize yields so that fertilizer applications keep increasing. We assessed the interaction between chemical phosphorus fertilizers, the establishment of mycorrhizal associations and biomass production of Cayenne, Champaka, and MD2 cultivars of pineapple in a greenhouse experiment. Plants were inoculated with a mycorrhizal consortium and grown with 0, 80, 200, 300, 500, and 600 mg phosphorus kg-1 soil additions in 8 kg pots for 8 months. Phosphorus reduced mycorrhizal colonization already at the lowest phosphorus fertilization dose in two of the three cultivars and became minimal for all cultivars from 200 mg P kg-1 soil. At the two highest phosphorus fertilization levels, shoot dry biomass and the dry weight of leaf D was reduced in all cultivars. The results show that the farmer´s practice of adding excessive fertilizer as an insurance principle is reaching the levels where fertilization is becoming detrimental for production and mycorrhizal benefits for the crop and the soil are being eliminated.