Mixed rhizobia and Herbaspirillum seropedicae inoculations with humic acid-like substances improve water-stress recovery in common beans

António Da Piedade Melo,Leonardo Barros Dobbss,Luciano Pasqualoto Canellas,Fábio Lopes Olivares,Leonardo Oliveira Médici,Alena Torres-Neto

doi:10.1186/s40538-017-0090-z

Abstract

BackgroundCommon beans are a staple food in many developing countries. However, changes in global precipitation patterns, particularly short droughts during the rainy season, have affected crop production because nodulation is greatly affected by water shortages. Plant growth-promoting bacteria, together with humic substances, can alleviate the negative effects of soil stresses, including drought.AimsThis work aimed to evaluate the effects of co-inoculations of rhizobia and Herbaspirillum seropedicae in the presence of humic acid-like substances isolated from vermicompost on the recovery of common beans after a controlled water stress.MethodsTwo independent experiments were conducted in a greenhouse using Phaseolus vulgaris cv. Grafite and cv. Bonus, which originated in Brazil and Mozambique, respectively. The soil humidity was maintained at field capacity in pots, and the water suppression was induced at the pre-flowering stage. After 12 days, the water was restored, and the beans were evaluated.ResultsIn the first experiment with ‘Grafite’ beans, the relative water content of the foliar disks was significantly higher in the co-inoculated treatment, as were the numbers and masses of nodules. The phenylalanine ammonia lyase activity was induced by drought, and its activity was higher in co-inoculated plant leaves. In the second experiment, the rate of net photosynthesis and stomatal conductance were also evaluated. The recuperation of common beans after water stress was improved by co-inoculation with rhizobia and H. seropedicae in the presence of humic acid-like substances.Graphical abstractThe relative water content increased (RWC%) with co-inoculation.

Highlights

Common beans are a staple food in many developing countries
The phenylalanine ammonia lyase activity was induced by drought, and its activity was higher in co-inoculated plant leaves
The recuperation of common beans after water stress was improved by co-inoculation with rhizobia and H. seropedicae in the presence of humic acid-like substances

Summary

Introduction

Common beans are a staple food in many developing countries. changes in global precipita‐ tion patterns, short droughts during the rainy season, have affected crop production because nodulation is greatly affected by water shortages. Plant growth-promoting bacteria, together with humic substances, can allevi‐ ate the negative effects of soil stresses, including drought. Biological nitrogen fixation (BNF) can reduce the use of fertilizers but the. (2017) 4:6 former involves the direct transfer of nutrients by BNF and increases the phosphorus (P) availability by mineral phosphate solubilization [5]. Decreases in drought stress-induced damage after the inoculation of different bacteria were observed [12, 13]. These effects were attributed to a reduction in the ethylene production by the bacterial enzyme aminocyclopropane-1-carboxylate deaminase and the maintenance of a normal level of plant endogenous abscisic acid [14]. Some reports on mixed inoculations of rhizobia and Azospirillum on common beans showed enhanced levels of nodulation [15, 16] and higher crop yields [7, 17]

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