Abstract
Witchweeds (Striga sp.) are parasitic weeds of great agricultural significance, parasitizing the roots of their hosts. Striga, like all other root parasitic weeds, drain essential organic and inorganic resources from their hosts leading to poor crop development and low yield. In Africa, about 50 million ha in over 30 countries are infested by Striga spp. causing grain loss of cereals. Estimated yield losses of maize, sorghum, millets and upland rice are between 30 and 90%. The parasite, therefore, is ranked as the leading biotic constraint to cereal production in the continent. Plant growth promoting rhizobacteria (PGPR) are promising components for integrated solutions to agro-environmental problems because inoculants possess the capacity to promote crop growth and reduce the population of deleterious microbes in the rhizosphere. Although there are numerous studies on crop growth promotion and biological control of diseases, weeds, nematodes and parasitic weeds using PGPR, little is known about the potential of some Bacillus subtilis, B. amyloliquefaciens and Burkholderia phytofirmans strains in sorghum growth promotion and resistance against Striga infection. The main objective of the study was to assess the effect of B. subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans PsJN on growth promotion of sorghum crop and suppression of Striga development, thus providing a basic understanding on the sorghum-PGPR-Striga interaction. This study opens with an elaborate review of the state-of-the-art knowledge on the tripartite interactions between Striga, sorghum and different species of PGPR. Prior to this, bipartite relationship between sorghum and Striga, PGPR-sorghum and PGPR-Striga are reviewed with a focus on understanding Striga impact on sorghum, sorghum defence responses to infection, plant growth and disease suppression benefits by PGPR on sorghum, and the effect of PGPR on Striga development. Knowledge gaps in both bipartite and tripartite relationships are described, and future research recommendations given. A key recommendation from the review is to conduct experiments under controlled environmental conditions using Bacillus subtilis, B. amyloliquefaciens and Burkhoderia phytofirmans strains in order to understand their relationship with sorghum and Striga at bipartite and tripartite levels. Petri dish bioassays and root chamber experiments under controlled conditions were conducted at the Institute of Plant Production and Agroecology in the Tropics and Subtropics, University of Hohenheim between 2012 and 2014. B. subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans strain PsJN inocula and their corresponding cell culture supernatants were evaluated for their growth promotion potential on sorghum and suppressiveness on Striga development. Sorghum root exudates and synthetic stimulant GR24 were used to induce Striga seed germination. Bacillus subtilis Bsn5 supernatant, which showed the greatest inhibitory activity on Striga germination and radicle elongation, was separated by ethyl acetate into lipophilic and hydrophilic phases. The purpose of this extraction was to try and identify the polarity of the inhibitor. Protein composition by mass spectrometry (MS) was also done on the supernatant with a view of establishing the presence of peptides because peptides have been associated with Orobancheceae germination and radicle inhibition in previous studies. In addition, determination of plant growth hormones in bacteria supernatants was also conducted using Radio-Immuno-Assay (RIA) in order to relate PGPR hormone production and sorghum growth enhancement. Burkholderia phytofirmans PsJN significantly (<0.05) induced a higher vigor index (VI) on sorghum seedlings (>18,000) compared to other PGPR and control treatments. The lowest VI (7626) was recorded in seeds inoculated with Bacillus amyloliquefaciens FZB42. Complete Striga germination inhibition (0% germination) occurred in seeds exposed to all PGPR inocula suspended while the highest germination (>60%) occurred in control treatments (10% Luria Bertani (LB) + GR24 and sterile distilled water (SDW) + GR24). The effect of bacterial supernatants on the germination percentage and radicle length of Striga seeds was also significantly (<0.05) different among treatments. The least germination (7.4 %) was observed in Bacillus subtilis Bsn5 + GR24 while the highest (66 %) was observed in SDW + GR24 control. Bacillus subtilis Bsn5 supernatant produced the lowest mean radicle lengths (0.1 mm) while the highest radicle lengths were observed in SDW + GR24 (2.2 mm). Therefore, Bacillus subtilis Bsn5 supernatant was selected for further investigation of compounds causing inhibition of Striga germination and preventing radicle elongation. The supernatant was separated into hydrophilic and hydrophobic fractions using ethyl acetate. Each fraction was then prepared in 1%, 25%, 50%, 75% and 100% concentrations before being evaluated for their inhibitory activity in Striga germination and radicle elongation. The highest germination percentage (63%) and radical length (2.9 mm) was observed in SDW + GR24 control treatment. The ethyl acetate (lipophilic) fraction at both 100% and 1% concentration + GR24 produced a germination percentage of >40% which was similar to 10% LB + GR24 and ethyl acetate + GR24 controls. There was complete inhibition of Striga seed germination after exposure to either Bacillus subtilis Bsn5 supernatant + GR24 or 100% hydrophilic fraction of the supernatant + GR24. However, at 25% and 1% concentration + GR24, Striga germination percentage increased to 34% and 49%, respectively. Light microscopy examination of Striga radicles exposed to Bacillus subtilis Bsn5 supernatant + GR24 revealed that stunting of the radicles was due to reduction in cell sizes at the radicle elongation zone. Extended agar gel assays (EAGA) experiments showed a similar trend of results with B. subtilis Bsn5 showing the highest inhibitory activity on Striga germination and radicle elongation compared to other PGPR and control treatments. Results from root chamber experiments demonstrated significant (p<0.05) differences in biomass production between Striga-free and Striga-infected sorghum. Total biomass yield in uninoculated Striga-free plants was 40% higher than uninoculated Striga-infected sorghum plants. Bacillus amyloliquefaciens FZB42, B. subtilis GBO3 and Burkholderia phytofirmans PsJN inoculated Striga-free sorghum showed a 75%; 142% and 158% increase in biomass yield, respectively, compared to uninoculated Striga-free sorghum. There were no significant differences in biomass yield observed between inoculated and uninoculated Striga-infected plants. All PGPR supernatants and 10% LB media showed production of phytohormones cytokinin, IAA, GAs and ABA. Cytokinin content in PGPR supernatants was significantly (>0.05) higher than blank 10% LB control media. There was a significant negative correlation (r= -0.96) between IAA and cytokinins. However, there was no significant positive correlation between any phytohormone and sorghum plant height, SPAD values, biomass production, Striga germination, attachment and tubercle death. Finally, this study shows that Bacillus subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans PsJN might accelerate sorghum growth and suppress key stages of Striga development under laboratory conditions. Greenhouse and field experiments are recommended to better understand these interactions under natural conditions where other biotic and abiotic factors come into play. These findings could contribute to a better understanding of sorghum and beneficial bacteria interactions and provide novel information of the long-term effects of a PGPR on sorghum development, opening new avenues for Striga control and sustainable, ecofriendly sorghum production.
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Claims 20
Claim · model-written summary
Burkholderia phytofirmans PsJN increased sorghum seedling vigor relative to other bacteria and controls, exceeding 18,000.
- Treatment
- Burkholderia phytofirmans PsJNe0
- Interactor
- Burkholderia phytofirmans PsJNParaburkholderia phytofirmans PsJNe0symbiont
- Outcome
- vigor index (VI)e0
- Direction
- highere0
- Value
- >18,000e0
- Comparator
- other PGPR and control treatmentse0
SorghumOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Burkholderia phytofirmans PsJN significantly (<0.05) induced a higher vigor index (VI) on sorghum seedlings (>18,000) compared to other PGPR and control treatments”
Claim · model-written summary
Bacillus amyloliquefaciens FZB42 inoculation gave the lowest sorghum vigor index, 7626.
- Treatment
- inoculated with Bacillus amyloliquefaciens FZB42e0
- Interactor
- Bacillus amyloliquefaciens FZB42Bacillus velezensis FZB42e0symbiont
- Outcome
- VIe0
- Direction
- loweste0
- Value
- 7626e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“The lowest VI (7626) was recorded in seeds inoculated with Bacillus amyloliquefaciens FZB42”
Claim · model-written summary
All tested PGPR inocula completely inhibited Striga seed germination compared with controls above 60%.
- Treatment
- all PGPR inocula suspendede0
- Outcome
- Striga germinatione0
- Direction
- Complete Striga germination inhibitione0
- Value
- 0% germinatione0
- Qualifier
- >60%e0
- Comparator
- control treatmentse0
StrigaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Complete Striga germination inhibition (0% germination) occurred in seeds exposed to all PGPR inocula suspended while the highest germination (>60%) occurred in control treatments (10% Luria Bertani (LB) + GR24 and sterile distilled water (SDW) + GR24)”
Claim · model-written summary
Bacillus subtilis Bsn5 supernatant with GR24 reduced Striga germination to 7.4% versus 66% in the water and GR24 control.
- Treatment
- Bacillus subtilis Bsn5 + GR24e0
- Outcome
- germinatione0
- Direction
- leaste0
- Value
- 7.4 %e0
- Qualifier
- 66 %e0
- Comparator
- SDW + GR24 controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“The least germination (7.4 %) was observed in Bacillus subtilis Bsn5 + GR24 while the highest (66 %) was observed in SDW + GR24 control”
Claim · model-written summary
Bacillus subtilis Bsn5 supernatant reduced Striga radicle length to 0.1 mm versus 2.2 mm in the water and GR24 control.
- Treatment
- Bacillus subtilis Bsn5 supernatante0
- Outcome
- radicle lengthse0
- Direction
- loweste0
- Value
- 0.1 mme0
- Qualifier
- 2.2 mme0
- Comparator
- SDW + GR24e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Bacillus subtilis Bsn5 supernatant produced the lowest mean radicle lengths (0.1 mm) while the highest radicle lengths were observed in SDW + GR24 (2.2 mm)”
Claim · model-written summary
The 100% lipophilic fraction allowed Striga germination above 40%.
- Treatment
- 100% and 1% concentration + GR24e0
- Outcome
- germination percentagee0
- Value
- >40%e0
- Comparator
- 10% LB + GR24 and ethyl acetate + GR24 controlse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“The ethyl acetate (lipophilic) fraction at both 100% and 1% concentration + GR24 produced a germination percentage of >40% which was similar to 10% LB + GR24 and ethyl acetate + GR24 controls”
Claim · model-written summary
Bacillus subtilis Bsn5 supernatant completely inhibited Striga germination.
- Treatment
- Bacillus subtilis Bsn5 supernatant + GR24e0
- Second interactor
- Bacillus subtilis Bsn5
Bacillus subtilis BSn5e0biocontrol_agent - Outcome
- Striga seed germinatione0
- Direction
- complete inhibitione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“There was complete inhibition of Striga seed germination after exposure to either Bacillus subtilis Bsn5 supernatant + GR24 or 100% hydrophilic fraction of the supernatant + GR24”
Claim · model-written summary
The 100% hydrophilic fraction completely inhibited Striga germination.
- Treatment
- 100% hydrophilic fraction of the supernatant + GR24e0
- Outcome
- Striga seed germinatione0
- Direction
- complete inhibitione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“There was complete inhibition of Striga seed germination after exposure to either Bacillus subtilis Bsn5 supernatant + GR24 or 100% hydrophilic fraction of the supernatant + GR24”
Claim · model-written summary
At 25% hydrophilic fraction concentration, Striga germination increased to 34%.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“However, at 25% and 1% concentration + GR24, Striga germination percentage increased to 34% and 49%, respectively”
Claim · model-written summary
At 1% hydrophilic fraction concentration, Striga germination increased to 49%.
- Treatment
- 1% concentration + GR24e0
- Outcome
- Striga germination percentagee0
- Direction
- increasede0
- Value
- 49%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“However, at 25% and 1% concentration + GR24, Striga germination percentage increased to 34% and 49%, respectively”
Claim · model-written summary
Bsn5 supernatant stunted Striga radicles through reduced cell size in the elongation zone.
- Treatment
- Bacillus subtilis Bsn5 supernatant + GR24e0
- Outcome
- stunting of the radiclese0
- Qualifier
- reduction in cell sizes at the radicle elongation zonee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Light microscopy examination of Striga radicles exposed to Bacillus subtilis Bsn5 supernatant + GR24 revealed that stunting of the radicles was due to reduction in cell sizes at the radicle elongation zone”
Claim · model-written summary
B. subtilis Bsn5 showed the greatest inhibition of Striga germination and radicle elongation in extended agar gel assays.
- Treatment
- B. subtilis Bsn5e0
- Second interactor
- B. subtilis Bsn5Bacillus subtilise0biocontrol_agent
- Outcome
- Striga germination and radicle elongatione0
- Direction
- highest inhibitory activitye0
- Comparator
- other PGPR and control treatmentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Extended agar gel assays (EAGA) experiments showed a similar trend of results with B. subtilis Bsn5 showing the highest inhibitory activity on Striga germination and radicle elongation compared to other PGPR and control treatments”
Claim · model-written summary
Uninoculated Striga-free sorghum had 40% greater biomass than uninoculated infected sorghum.
- Treatment
- Striga-freee0
- Outcome
- Total biomass yielde0
- Direction
- highere0
- Value
- 40%e0
- Comparator
- Striga-infected sorghum plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Total biomass yield in uninoculated Striga-free plants was 40% higher than uninoculated Striga-infected sorghum plants”
Claim · model-written summary
FZB42 inoculation increased Striga-free sorghum biomass by 75% versus uninoculated plants.
- Treatment
- Bacillus amyloliquefaciens FZB42e0
- Interactor
- Bacillus amyloliquefaciens FZB42Bacillus velezensis FZB42e0symbiont
- Outcome
- biomass yielde0
- Direction
- increasee0
- Value
- 75%e0
- Comparator
- uninoculated Striga-free sorghume0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Bacillus amyloliquefaciens FZB42, B. subtilis GBO3 and Burkholderia phytofirmans PsJN inoculated Striga-free sorghum showed a 75%; 142% and 158% increase in biomass yield, respectively, compared to uninoculated Striga-free sorghum”
Claim · model-written summary
GBO3 inoculation increased Striga-free sorghum biomass by 142% versus uninoculated plants.
- Treatment
- B. subtilis GBO3e0
- Interactor
- B. subtilis GBO3Bacillus subtilise0symbiont
- Outcome
- biomass yielde0
- Direction
- increasee0
- Value
- 142%e0
- Comparator
- uninoculated Striga-free sorghume0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Bacillus amyloliquefaciens FZB42, B. subtilis GBO3 and Burkholderia phytofirmans PsJN inoculated Striga-free sorghum showed a 75%; 142% and 158% increase in biomass yield, respectively, compared to uninoculated Striga-free sorghum”
Claim · model-written summary
PsJN inoculation increased Striga-free sorghum biomass by 158% versus uninoculated plants.
- Treatment
- Burkholderia phytofirmans PsJNe0
- Interactor
- Burkholderia phytofirmans PsJNParaburkholderia phytofirmans PsJNe0symbiont
- Outcome
- biomass yielde0
- Direction
- increasee0
- Value
- 158%e0
- Comparator
- uninoculated Striga-free sorghume0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Bacillus amyloliquefaciens FZB42, B. subtilis GBO3 and Burkholderia phytofirmans PsJN inoculated Striga-free sorghum showed a 75%; 142% and 158% increase in biomass yield, respectively, compared to uninoculated Striga-free sorghum”
Claim · model-written summary
Bacterial inoculation did not yield a significant biomass difference in Striga-infected sorghum.
- Treatment
- inoculatede0
- Outcome
- biomass yielde0
- Direction
- no significant differencese0
- Comparator
- uninoculated Striga-infected plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“There were no significant differences in biomass yield observed between inoculated and uninoculated Striga-infected plants”
Claim · model-written summary
PGPR supernatants and LB medium contained cytokinin, IAA, GAs and ABA.
- Outcome
- production of phytohormones cytokinin, IAA, GAs and ABAe0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“All PGPR supernatants and 10% LB media showed production of phytohormones cytokinin, IAA, GAs and ABA”
Claim · model-written summary
IAA and cytokinin concentrations were strongly negatively correlated.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“There was a significant negative correlation (r= -0.96) between IAA and cytokinins”
Claim · model-written summary
The authors recommend greenhouse and field experiments to examine bacterial effects on sorghum and Striga in natural conditions.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“sorghum growth and biotic suppression of striga infestation”
e0“Greenhouse and field experiments are recommended to better understand these interactions under natural conditions where other biotic and abiotic factors come into play”
The same questions in other papers
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See all 9 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.