Azospirillum brasilense and Zinc Rates Effect on Fungal Root Colonization and Yield of Wheat-Maize in Tropical Savannah Conditions

Abstract

A successful microbial inoculant can increase root colonization and establish a positive interaction with native microorganisms to promote growth and productivity of cereal crops. Zinc (Zn) is an intensively reported deficient nutrient for maize and wheat production in Brazilian Cerrado. It can be sustainably managed by inoculation with plant growth-promoting bacteria and their symbiotic association with other microorganisms such as arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE). The objective of this study was to evaluate the effect of Azospirillum brasilense inoculation and residual Zn rates on root colonization and grain yield of maize and wheat in succession under the tropical conditions of Brazil. These experiments were conducted in a randomized block design with four replications and arranged in a 5 × 2 factorial scheme. The treatments consisted of five Zn rates (0, 2, 4, 6 and 8 kg ha−1) applied from zinc sulfate in maize and residual on wheat and without and with seed inoculation of A. brasilense. The results indicated that root colonization by AMF and DSE in maize–wheat cropping system were significantly increased with interaction of Zn rates and inoculation treatments. Inoculation with A. brasilense at residual Zn rates of 4 kg ha−1 increased root colonization by AMF under maize cultivation. Similarly, inoculation with A. brasilense at residual Zn rates of 2 and 4 kg ha−1 reduced root colonization by DSE under wheat in succession. The leaf chlorophyll index and leaf Zn concentration were increased with inoculation of the A. brasilense and residual Zn rates. The inoculation did not influence AMF spore production and CO2-C in both crops. The grain yield and yield components of maize–wheat were increased with the inoculation of A. brasilense under residual Zn rates of 3 to 4 kg ha−1 in tropical savannah conditions. Inoculation with A. brasilense under residual Zn rates up to 4 kg ha−1 promoted root colonization by AMF and DSE in the maize cropping season. While the inoculation with A. brasilense under 2 and 4 kg ha−1 residual Zn rates reduced root colonization by AMF and DSE in the wheat cropping season. Therefore, inoculation with A. brasilense in combination with Zn fertilization could consider a sustainable approach to increase the yield and performance of the maize–wheat cropping system in the tropical savannah conditions of Brazil.

Importance of Dark Septate Endophytes in Agriculture in the Face of Climate Change

“…Thus, the combined use of Agrobacterium pusense isolated from the DSE Veronaeopsis simplex in tomatoes resulted in an increased number of roots colonised by the fungus. The same finding was observed by Silva et al [158], who described that the root colonisation by AMF and DSEs can be increased by the application of Azospirillum brasilense. Wu et al [172] observed a high colonisation rate of mycorrhizal fungi with DSEs in C. korshinskii roots, which indicated the existence of symbiotic relationships between them, as well as with Rhizobium under desert conditions.…”

Interaction of Zinc Mineral Nutrition and Plant Growth-Promoting Bacteria in Tropical Agricultural Systems: A Review

“…Several Zn solubilizing bacteria are being reported as sustainable alternatives that could not only improve Zn content but also enhance phosphorous and potassium solubilization; nitrogen fixation; and production of phytohormones (kinetin, indole-3-acetic acid, and gibberellic acid), as well as the synthesis of siderophores; hydrogen cyanide; and ammonia. All these factors together discourage the use of synthetic fertilizers by promoting plant growth, productivity, and soil fertility status [ 21 , 93 , 94 ]. Thus, inoculation with PGPBs could be one of the best transmission tools to optimize the harnessing of climate change to better understand the establishment of sustainable agriculture.…”

Azospirillum brasilense Inoculation in a Maize–Urochloa–Rice Cropping System Promotes Soil Chemical and Biological Changes and Increases Productivity

“…Bacteria, such as those of the genus Azospirillum, have been recommended for their ability to synthesize plant growth phytohormones such as auxins, gibberellins and cytokinins, in addition to acting on phosphate solubilization and inducing the intrinsic systemic resistance of the plant to abiotic and biotic stresses [11,12]. The increase in the root system due to the synthesis of phytohormones allows plants to exploit a larger area of soil for water and nutrients, increasing crop productivity [13,14].…”