**4. PGPR reduce chemical fertilization**

and Labandera-Gonzalez reported that 60–70% of the experiments showed yield increases due

*Pseudomonas* strains significantly increased grain yield of wheat [23, 49, 143, 166]. Similarly, Shaharoona et al. reported that N use efficiency increased in response to inoculation with *Pseudomonas fluorescens* at all fertilizer levels in wheat [167]. PGPR isolates significantly increased shoot and root length, shoot and root dry weight, grain weight per spike, shoot and root N content and also enhanced the N contents of inoculated wheat seedlings [168]. Barneix et al. reported that inoculation of wheat with *Bacillus simplex* and *Bacillus firmis* resulted in consistent increase in dry matter and wheat grain quality. A number of other *Bacillus* spp. isolated from wheat rhizosphere have also been investigated for their growth-promoting property in wheat having similar effects on dry weight [10, 40, 169], the latter focusing on isolating and characterizing PGPRs. Trials with rhizosphere-associated plant growth-promoting


Inoculation with mixed different strains could be an alternative to inoculation with individual strains, likely reflecting the different mechanisms used by each strain in the consortium [173].

tive than a single microorganism for providing a more balanced nutrition for plants [19, 174]. There are numerous examples in wheat whereby synergistic effects of multiple PGPRs are observed [97, 175, 176]. Among those, notable is the combined inoculation of mixtures and biofilmed bio-inoculants (*Anabaena torulosa* + *Pseudomonas striata* and/or *Anabaena torulosa* + *Azotobacter chroococcum*) were superior over single inoculation and chemical fertilizer control in term of plant growth and nutrient uptake [177]. The benefits can be on nutrient uptake, but also in root physiology as exemplified by Manjunath et al. as co-inoculation of wheat with two proteobacterial (*Providencia* sp. and *Alcaligenes* sp.) and two cyanobacterial (*Anabaena* 

Seed bacterization with both strains, *P. fluorescens* BAM-4 and *B. cepacia* BAM-12 single or combined significantly enhanced growth and yield, but increase in bacterial population, spike length, P content of shoots and grain yield was more in co-inoculation treatment than single. The best among the bioinoculation treatments was *B. cepacia* BAM-12 + TCP and *B. cepacia* BAM-12 + *P. fluorescens* BAM-4 + TCP for P content with free and immobilized cells [180].

Several authors conducted experiments on wheat either under pot and field conditions to examine the effect of co-inoculations of PGPR on the growth and yield of wheat. Kumar et al. found that *B. megaterium, A. chlorophenolicus* and *Enterobacter* significantly increased plant height, grain yield and straw yield [181]; Baris et al. concluded that *Bacillus megaterium* M3 and Mixed (*Bacillus subtilis* 05U142, *B. megaterium* M3, *Azospirillum brasilense* Sp245) inoculation provided greater plant nutrient element concentrations than mineral fertilizer application


to inoculation, with statistically significant increases in yield from 5 to 30% [31].

ing grain yield, grain protein concentration or both [3, 135, 140, 164, 172].

*oscillarioides* and *Anabaena torulosa*) inoculants, similarly in Ref. [178, 179].

**3. Co-inoculation of multiple PGPRs**

Combined inoculation with N<sup>2</sup>

130 Wheat Improvement, Management and Utilization

N2

Due to high cost of chemical fertilizers and negative environmental effects, the use of PGPR as biofertilizer is advantageous for development of sustainable agriculture, increasing agronomic efficiency, once the use of chemical fertilizers can be reduced or eliminated if the inoculants are efficient [6]. The use of bio-fertilizers with a good management can decrease the leaching loss of nitrate and phosphate from the agricultural land and improve the ground water quality [190]. Also, the use of PGPR with low-fertilizer rate is also an environment friendly step and would be a viable supplementary strategy for further increasing crop yields [71, 78, 191].

Trials conducted under greenhouse conditions showed that most of PGPR in the absence of any fertilizer application achieved increases in root and shoot weight [3], corresponding to nitrogen treatment at the rate of 40 and 80 kg N ha−1 in wheat. Furthermore, co-inoculation of N<sup>2</sup> -fixing and P-solubilizing bacteria always gave equal or higher grain yield than conventional application of nitrogen.

Rosas et al. studied the promotion effect of *Pseudomonas aurantiaca* SR1 on maize and wheat in field treatments that included phosphorus and nitrogen fertilization [166]. Both crops, when inoculated with the SR1 strain, presented significant promoting effect in growth parameters and higher yields with lower fertilization doses than conventionally applied. Additionally, PGPR are also important with respect to an efficient use of resources such as P and N, as illustrated by a 95% increased P use efficiency of wheat grains [163].

It could be concluded that application of PGPR with low-fertilizer rates could be a viable supplementary strategy for maximum benefits and should be employed with appropriate doses of fertilizers to get maximum benefit in terms of fertilizer savings and better growth in any yield of crops. Experiments as field trials with dry land areas, the co-inoculations of PGPR strains for wheat, maize and barley with chemical fertilizers gave improved response [3, 183, 192–197].
