Abstract al., 2009; Grover et al., 2011, Glick, 2012).

Abstract

Plant
growth promoting rhizobacteria (PGPR) are bacteria found in the rhizosphere of
plants that have been shown by a number of studies to enhance plant growth by a
number of mechanisms both directly and directly for instance by production of
plant growth promoting hormones, phosphate and mineral solubilization,
production of volatile organic compounds and nitrogen fixation. The potential use
of such microorganisms in agriculture is currently feign explored worldwide as
alternative ways to replace the use of chemical fertilizers and pesticides. The
understanding of the diversity of PGPR in different plant rhizospheres as well
as their colonization ability and mechanisms of action will enable their rapid
application in agriculture for sustainability of the environment. This article
reviews the studies which have been done to assess the potential of PGPR for
improved crop production and productivity in Africa.

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Keywords: PGPR,
Rhizosphere bacteria, Plant-microbe interactions, crop production, agriculture

 

Introduction

Over
the past few decades, there have been increase in intensive and extensive
agricultural activities worldwide in an attempt to feed the ever-rising
population of people. Along with this, unanticipated environmental problems
have come up due to the continuous usage of chemical fertilizers and pesticides
to enhance crop productivity and control crop pests respectively (Alves et al.,
2004; Hungria et al., 2013).  In an
attempt to move towards sustainable agricultural practices and to maintain the
ecosystems and biodiversity, interests have been shifted towards the potential of
indigenous plant growth promoting rhizobacteria for improved and sustainable crop
production and productivity (Alves et al., 2004; Hungria et al., 2013). Several studies have been done
on the potential of these microbes even in crops.

The
term Plant Growth Promoting Rhizobacteria (PGPR) is used to refer to soil
bacteria that colonize the rhizosphere of plants, growing in or around plant
tissues and that stimulate plant growth by different mechanisms (Dimpka et al.,
2009; Grover et al., 2011, Glick, 2012). The direct mechanisms by which PGPR promote
plant growth include biofertilization, stimulation of root growth,
rhizoremediation and plant stress control, while indirect mechanisms include
bio-protection by means of antibiosis, induction of systemic resistance, and
competition against plant pathogens for nutrients and niches (Lugtenberg and
Kamilova, 2009).  Common PGPR genera that
have been found to be commonly associated with different crops include Acinetobacter,
Alcaligenes, Arthrobacter, Azospirillum, Azotobacter,
Bacillus, Beijerinckia, Burkholderia, Enterobacter,
Erwinia, Flavobacterium, Rhizobium and Serratia
(Anandarai and Dinesh, 2008).

In
this article, we review the different mechanisms of plant growth promotion, we
look at examples of crops whose rhizobacteria have been studied for growth
promotion and we also look at the gaps which exist in the studies of PGPR.

Mechanisms of growth
promotion

Bio-protection

Numerous
studies have reported plant growth promotion potential of PGPR as a result of
controlling plant pests. Recently, Son et al., (2014) found that among selected PGPR isolates,
four significantly decreased gray leaf spot disease severity with PGPR Brevibacterium iodinum KUDC1716
providing the highest disease suppression in pepper (Capsicum annuum). It was also found
that P. polymyxa increased plant growth
of pepper (C. annuum) by decreasing the
severity of Xanthomonas axonopodis pv. Vesicatoria (Quyet-Tien et al., 2010).

 

Studied
crops

Research exploring the
potential of PGPR for increased crop production and productivity has beed done
by several researchers. The common knowledge now is that all plants harbor a
diverse community of indigenous bacteria in their rhizosphere which help
stimulate their growth naturally. Studies have shown that PGPR had
positive effects on cereals (Shararoona et al., 2006), fruits (Kavino et al.,
2010), vegetables (Kurabachew and Wydra, 2013), flowers (An et al, 2010) and
spices like black pepper (Diby and Sarma, 2006).

 

Gaps
in knowledge

It
is apparent that numerous studies have been done on isolation of PGPR and how
they affect growth and yield of many crops worldwide. However, several knowledge
gaps still remain to be filled. For example, very little has been done but
little is known concerning potassium solubilization while potassium is the
third major macronutrient for plant growth.

 

Conclusions

The
most urgent need of the world today is to increase the output and yield of
crops by means of soil fertilization and control of pests. The application and
use of PGPR can help achieve these two necessities while maintaining the ecosystems
at the same time.

 

References

Y. An, S. Kang, K.D. Kim, B.K.
Hwang, Y. JeunEnhanced defense responses of tomato plants against late
blight pathogen Phytophthora infestans by pre-inoculation with
rhizobacteria

Crop Prot, 29 (2010), pp. 1406-1412

 

M. Anandaraj, R. DineshUse of
microbes for spices production

V.A. Parthasarathy, K. Kandiannan,
V. Srinivasan (Eds.), Organic spices, New India Publishing Agency, New Delhi
(2008), pp. 101-132

 

P. Diby, Y.R. SarmaPlant growth
promoting rhizhobacteria (PGPR)-mediated root proliferation in black pepper (Piper
nigrum L.) as evidenced through GS Root software

Arch Phytopathol Plant Prot, 39
(2006), pp. 311-314

 

R. Dinesh, M. Anandaraj, A. Kumar,
V. Srinivasan, Y.K. Bini, K.P. Subila, et al.Effects of plant growth
promoting rhizobacteria and NPK fertilizers on biochemical and microbial
properties of soils under ginger (Zingiber officinale Rosc.) cultivation

Agric Res, 2 (2013), pp. 346-353

 

M. Kavino, S. Harish, N. Kumar, D. Saravanakumar,
R. SamiyappanEffect of chitinolytic PGPR on growth, yield and physiological
attributes of banana (Musa spp.) under field conditions

Appl Soil Ecol, 45 (2010), pp. 71-77

 

H. Kurabachew, K. WydraCharacterization
of plant growth promoting rhizobacteria and their potential as bioprotectant
against tomato bacterial wilt caused by Ralstonia solanacearum

Biol Control, 67 (2013), pp. 75-83

 

P. Quyet-Tien, Y.M. Park, K.J. Seul,
C.-M. Ryu, S.H. Park, J.C. Kim, et al.Assessment of root-associated Paenibacillus
polymyxa groups on growth promotion and induced systemic resistance in
pepper

J Microbiol Biotechnol, 20 (2010),
pp. 1605-1613

 

B. Shaharoona, M. Arshad, Z.A.
Zahir, A. KhalidPerformance of Pseudomonas spp. containing
ACC-deaminase for improving growth and yield of maize (Zea mays L.) in
the presence of nitrogenous fertilizer

Soil Biol Biochem, 38 (2006), pp.
2971-2975

 

J.-S. Son, M. Sumayo, Y.-J. Hwang,
B.-S. Kim, S.-Y. GhimScreening of plant growth-promoting rhizobacteria as
elicitor of systemic resistance against gray leaf spot disease in pepper

Appl Soil Ecol, 73 (2014), pp. 1-8

 

B. Lugtenberg, F. KamilovaPlant-growth-promoting
rhizobacteria

Ann Rev Microbiol, 63 (2009), pp.
541-556

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