**4. Bacteria in biological weed control**

A number of bacterial species have been studied due to their potential against weed management (**Table 3**). Two major classes of rhizobacteria that show herbicidal activity are *Pseudomonas* and *Xanthomonas* sp. Different rhizobacterial species have been investigated as weed control agents on different crops based on their secondary metabolites [115, 116]. As stated earlier *Pseudomonas* have gained much importance as an agent in biological weed management; there are many strains of this genera, some are plant beneficial [117] and others can have inhibitory effects on plants [118] and so can be applied in biological weed control. Production of extracellular metabolites from these strains is a key mechanism in inhibition of plant growth or germination inhibition [118–120]. However several other mechanisms showing herbicidal activity of bacteria are shown in **Figure 2**.

A strain of *Pseudomonas fluorescens* (D7) isolated from wheat and downy brome rhizosphere has shown inhibitory effects on a number of grassy weeds especially downy brome by virtue of production of a phytotoxin [116, 119, 121]. Kremer et al. [122] tested the phytopathogenic ability of different *fluorescent* and non*fluorescent pseudomonads* which were isolated from the rhizosphere of seven important weeds. About 18% of the strains show phytopathogenecity. However, the ratio of isolates that inhibited seedlings was ranged between 35 and 65%. The mechanism behind is the production of antibiotics, and about 75% of the isolates were active in siderophore production.

Kennedy et al. [121] reported the differential weed inhibition ability of *Pseudomonads* for downy brome and winter wheat. When the culture filtrates were tested on agar, about 8% of the isolates reduced the root growth of downy brome but have no effects on the root growth of wheat. However, under soil application only less than 1% inhibited the growth of downy brome. In the field study, only 0.2% of the total 1000 isolates inhibited the growth of downy brome but increased the growth of winter wheat by 18–35%. Kremer [123] worked with different cover crops associated with deleterious rhizobacteria. Seed bacterization with DRB reduces growth and biomass in weeds associated with cover crops. Adam and Zdor [124] described that rhizobacteria isolated from the rhizosphere of *Abutilon theophrasti* Medik caused growth inhibition of different weeds.

Weissmann and Gerhardson [125] suggested that the application of strain (A153) on *Chenopodium album* suppressed the growth of plants for 10–14 days; however in field conditions, this effect lasts for 2 months. Similarly Weissmann et al. [126] demonstrated excellent growth inhibition ability of a strain (A153) belonging to soil bacteria *Serratia plymuthica* when sprayed on a number of broadleaved weeds. However, in field experiment this strain showed differential effects on *C. album*, *Stellaria media*, *Polygonum convolvulus*, and *Galeopsis speciosa*. Li and Kremer [127] suggested that the inoculation of *Pseudomonas fluorescens* strain (G2–11) inhibited the growth of *Ipomoea* sp. and *Convolvulus arvensis* weeds and increased the growth of wheat and soybean crops. Zermane et al. [128] in a study stated that *P. fluorescens* has the possible potential to control *Orobanche crenata* and *O. foetida* (*Broomrape*).

**Microbe(s)**

**255**

*Pseudomonas*

*Streptomyces*

*Streptomyces* sp. 0H-5093

*Streptomyces* sp. *Thermoactinomyces*

*Streptomyces*

*Fusarium* and *Flavobacterium* sp.

*Enterobacter*

*Pseudomonas*

*Streptomyces*

*Pseudomonas*

*Pseudomonas*

 *syringae* pv. *tagetis*

Annual bluegrass

Field

 ND

 *syringae* strain 3366

 Corn spurry and fireweed

 Pot

Phytotoxin

 production

 *saganonensis*

Barnyard grass, goose grass,

ND

 Herbicidine

 (vi)

> and tufted manna grass

 *fluorescens*

Leafy spurge

Field

 Auxin production

 to phytotoxic levels

 Reduced cell membrane integrity, inhibited

root growth Biocontrol activity

Germination

shoot growth Greater than 70% weed control

 inhibition, reduced root, and

[79]

[57]

 *taylorae*

Bindweed

Axenic

 IAA production

Sugar beet

Axenic

 IAA production

*Rhizoctonia* sp.

Leafy spurge

Greenhouse

production

Exopolysaccharide

 and HCN

 *hygroscopicus*

*Barnyard grass*

Pot

Antimicrobial

due to

 and herbicidal activity

Germination

reduction in stem, and leaf structure of

weed

Biocontrol activity on leafy spurge leading

[76]

*Application Potentials of Plant Growth Promoting Rhizobacteria and Fungi as an Alternative…*

[67]

[77]

[60]

[78]

to significant growth suppression Decreased root elongation and increased

shoot to root ratio 90.5% reduction in root growth, phytotoxic

activity

 inhibition, significant

[75]

hydantocidine

 production

 sp. A-6019

*Lemna minor*

Axenic

 Herbicidal activity and 5<sup>0</sup>

deoxyguanosine

 production


ND

 *chromofuscus* cluster

 Barnyard grass

Reddish Reddish

Axenic

 Cellulose inhibition and

production

phthoxazolin

 A

Significant growth inhibition due to

cellulose inhibition

 *fluorescens*

Sour cherry

 **involved**

**Target weed(s)**

 **Growth**

**Mechanism(s)**

**Observed** 

**effects/comments**

 **References**

[71]

[72]

[73]

[74]

*DOI: http://dx.doi.org/10.5772/intechopen.86339*

[72]

**condition(s)**

Pot Axenic

Axenic

 Antifungal activity and production

chlorothreonine

 Antibiosis and H2S production

IAA production

Significant loss in root weight

 ND

> of 4-

Significant growth inhibition


#### *Application Potentials of Plant Growth Promoting Rhizobacteria and Fungi as an Alternative… DOI: http://dx.doi.org/10.5772/intechopen.86339*

non-inoculated plants, hence positively influencing plant growth. Ambrosini et al. [114] suggested that sunflower-associated *Burkholderia* strains were found to be solubilizing Ca3(PO4)2, hence availing phosphorus for plant use. The management of soil, plant, and environmental interactions evidenced by boosted crop yields is gaining much attention globally. Moreover, agricultural inoculants (cultures) contain plant beneficial bacteria that help plants to meet the demands for nutrients.

A number of bacterial species have been studied due to their potential against weed management (**Table 3**). Two major classes of rhizobacteria that show herbicidal activity are *Pseudomonas* and *Xanthomonas* sp. Different rhizobacterial species have been investigated as weed control agents on different crops based on their secondary metabolites [115, 116]. As stated earlier *Pseudomonas* have gained much importance as an agent in biological weed management; there are many strains of this genera, some are plant beneficial [117] and others can have inhibitory effects on plants [118] and so can be applied in biological weed control. Production of extracellular metabolites from these strains is a key mechanism in inhibition of plant growth or germination inhibition [118–120]. However several other mechanisms

A strain of *Pseudomonas fluorescens* (D7) isolated from wheat and downy brome rhizosphere has shown inhibitory effects on a number of grassy weeds especially downy brome by virtue of production of a phytotoxin [116, 119, 121]. Kremer et al. [122] tested the phytopathogenic ability of different *fluorescent* and non*fluorescent pseudomonads* which were isolated from the rhizosphere of seven important weeds. About 18% of the strains show phytopathogenecity. However, the ratio of isolates that inhibited seedlings was ranged between 35 and 65%. The mechanism behind is

Kennedy et al. [121] reported the differential weed inhibition ability of *Pseudomonads* for downy brome and winter wheat. When the culture filtrates were tested on agar, about 8% of the isolates reduced the root growth of downy brome but have no effects on the root growth of wheat. However, under soil application only less than 1% inhibited the growth of downy brome. In the field study, only 0.2% of the total 1000 isolates inhibited the growth of downy brome but increased the growth of winter wheat by 18–35%. Kremer [123] worked with different cover crops associated with deleterious rhizobacteria. Seed bacterization with DRB reduces growth and biomass in weeds associated with cover crops. Adam and Zdor [124] described that rhizobacteria isolated from the rhizosphere of *Abutilon theophrasti* Medik

Weissmann and Gerhardson [125] suggested that the application of strain (A153) on *Chenopodium album* suppressed the growth of plants for 10–14 days; however in field conditions, this effect lasts for 2 months. Similarly Weissmann et al. [126] demonstrated excellent growth inhibition ability of a strain (A153) belonging to soil bacteria *Serratia plymuthica* when sprayed on a number of broadleaved weeds. However, in field experiment this strain showed differential effects on *C. album*, *Stellaria media*, *Polygonum convolvulus*, and *Galeopsis speciosa*. Li and Kremer [127] suggested that the inoculation of *Pseudomonas fluorescens* strain (G2–11) inhibited the growth of *Ipomoea* sp. and *Convolvulus arvensis* weeds and increased the growth of wheat and soybean crops. Zermane et al. [128] in a study stated that *P. fluorescens* has the possible potential to control *Orobanche crenata* and

the production of antibiotics, and about 75% of the isolates were active in

**4. Bacteria in biological weed control**

*Sustainable Crop Production*

siderophore production.

*O. foetida* (*Broomrape*).

**254**

caused growth inhibition of different weeds.

showing herbicidal activity of bacteria are shown in **Figure 2**.


**Microbe(s)**

**257**

*Pseudomonas*

*syringae*, and

*T.*  and *T. viride* *Trichoderma*

*Trichoderma*

*Trichoderma*

*Trichoderma*

*Trichoderma*

composted chicken manure and rye

*ND = not described.*

**Table 3.** *Features of* 

*opportunistic*

 *bacteria and fungi in weed control under varying growth conditions.*

 *virens*

combined with

Multiple broadleaf and

Field

 Viridiol

and

2,4-dihydroxy-1,4-(2H)

benzoxazine-3-one

production

 (DIBOA)

(3H)-benzoxazolinone

 (BOA)

Significant reductions in the emergence of

broadleaf and grassweeds reductions in weed biomass was resulted with all treatments as compared to control

 and higher

[93]

*Application Potentials of Plant Growth Promoting Rhizobacteria and Fungi as an Alternative*

*…*

grassweeds

 *viride* Pers

 *reesei*

*pseudokoningii*

 Rifai, Simmons, and

 *harzianum* Rifai,

*Phalaris minor* L. and

Laboratory

 Synthesis of butanol, n-hexane,

chloroform,

 and ethyl acetate

*Rumex dentatus* L.

*harzianum*,*T.*

*pseudokoningii*,*T.*

 *reesei*,

*Avena fatua* L.

Laboratory

 ND

 *aeruginosa*, *Pseudomonas*

 *alcaligenes*

*Pseudomonas*

Broad-leaved

common lambs' quarter

 dock,

Pot and field HCN production,

 IAA production,

Grain yield losses of infested wheat were

recovered up to 11.6 to 68% in pot trial, and

17.3 to 62.9% in field trial, respectively

Culture filtrates of four

significantly

and biomass of *Avena fatua*

Original

root and shoot length and biomass of *Rumex*

*dentatus* growth of *Phalaris minor* was not significant

significantly,

 but effect on shoot

concentration

 of filtrates reduced

[92]

*DOI: http://dx.doi.org/10.5772/intechopen.86339*

 reduced root, shoot growth,

*Trichoderma* spp.

[91]

antibiotic production

 **involved**

**Target weed(s)**

 **Growth**

**Mechanism(s)**

**Observed** 

**effects/comments**

 **References**

[34]

**condition(s)**


#### **Table 3.**

*Features of opportunistic bacteria and fungi in weed control under varying growth conditions.*
