Soil salinization is one of the most serious abiotic stress factors affecting plant productivity through reduction of soil water potential, decreasing the absorptive capacity of the roots for water and nutrients. A weighted meta-analysis was conducted to study the effects of arbuscular mycorrhizal fungi (AMF) inoculation in alleviating salt stress in C
3
and C
4
plants. We analyzed the salt stress influence on seven independent variables such as chlorophyll, leaf area, photosynthetic rate (
Amax
), stomatal conductance (
Gs
), transpiration rate (
E
), relative water content (RWC), and water use efficiency (WUE) on AMF inoculated plants. Responses were compared between C
3
and C
4
plants, AMF species, plant functional groups, level of salinity, and environmental conditions. Our results showed that AMF inoculated plants had a positive impact on gas exchange and water status under salt stress. The total chlorophyll contents of C
3
plants were higher than C
4
plants. However, C
3
plants responses regarding
Gs, Amax
, and
E
were more positive compared to C
4
plants. The increase in
G
s
mainly maintained
E
and it explains the increase in
Amax
and increase in
E
. When the two major AMF species (
Rhizophagus intraradices
and
Funnelliformis mosseae
) were considered, the effect sizes of RWC and WUE in
R. intraradices
were lower than those in
F. mosseae
indicating that
F. mosseae
inoculated plants performed better under salt stress. In terms of C
3
and C
4
plant photosynthetic pathways, the effect size of C
4
was lower than C
3
plants indicating that AMF inoculation more effectively alleviated salt stress in C
3
compared to C
4
plants.
Salinity is one of the major factors contributing to the loss of crop productivity and thereby impacting livelihood of people in more than 100 countries of the world and the area of land affected by salinity is increasing day by day. This will worsen due to various factors such as drought that might result in high soil salinity. Use of plant growth promoting rhizobacteria is one of the promising eco-friendly strategies for salinity stress management as part of sustainable agricultural practices. However, it requires selecting rhizobacteria with good survivability and adaptation to salt stress. In this study we report aggregation of Methylobacterium oryzae CBMB20 cells grown in media containing high C/N ratio (30:1) than in media containing low C/N ratio (7:1). Aggregated Methylobacterium oryzae CBMB20 cells exhibited enhanced tolerance to UV irradiation, heat, desiccation, different temperature regimes, oxidative stress, starvation and supported higher population in media. Poly-β-hydroxybutyrate accumulation, exopolysaccharide production, proline accumulation and biofilm formation were good at 100 mM salt concentration with good microbial cell hydrophobicity at both 50 and 100 mM than other concentrations. Both the aggregated and non-aggregated cells grown under 0–200 mM salt concentrations produced IAA even at 200 mM salt concentration with a peak at 100 mM concentration with aggregated cells producing significantly higher quantities. ACC deaminase activity was observed in all NaCl concentrations studied with gradual and drastic reduction in aggregated and non-aggregated cells over increased salt concentrations.
Arbuscular mycorrhizal fungi (AMF) spore propagation and long term maintenance is still a complicated technique for farmers. The use of AMF for their ability to promote plant growth and protect plants against pathogen attack and environmental stresses demands AMF propagation for large scale application. This study aimed to propagate AMF spores by trap culture technique and assess their ability to propagate with different host plants in a continuous plant cycle. Mycorrhizal inoculation by trap culture in maize resulted in longer shoots and roots than sudangrass plants. Increase in dry weight with higher percentage also was observed for maize plants. After first and second plant cycle, maize plants had the higher percentage of mycorrhizal response in terms of colonization and arbuscules than sudangrass. Maximum in spore count also achieved in the pots of maize plants. The results show that maize plant is more suitable host plant for AMF spore propagation and trap culture technique can be used effectively to maintain the AMF culture for long time.
Soil salinization refers to the buildup of salts in soil to a level toxic to plants. The major factors that contribute to soil salinity are the quality, the amount and the type of irrigation water used. The presented review discusses the different sources and causes of soil salinity. The effect of soil salinity on biological processes of plants is also discussed in detail. This is followed by a debate on the influence of salt on the nutrient uptake and growth of plants. Salinity decreases the soil osmotic potential and hinders water uptake by the plants. Soil salinity affects the plants K uptake, which plays a critical role in plant metabolism due to the high concentration of soluble sodium (Na + ) ions. Visual symptoms that appear in the plants as a result of salinity include stunted plant growth, marginal leaf necrosis and fruit distortions. Different strategies to ameliorate salt stress globally include breeding of salt tolerant cultivars, irrigation to leach excessive salt to improve soil physical and chemical properties. As part of an ecofriendly means to alleviate salt stress and an increasing considerable attention on this area, the review then focuses on the different plant growth promoting bacteria (PGPB) mediated mechanisms with a special emphasis on ACC deaminase producing bacteria. The various strategies adopted by PGPB to alleviate various stresses in plants include the production of different osmolytes, stress related phytohormones and production of molecules related to stress signaling such as bacterial 1-aminocyclopropane-1-carboxylate (ACC) derivatives. The use of PGPB with ACC deaminase producing trait could be effective in promoting plant growth in agricultural areas affected by different stresses including salt stress. Finally, the review ends with a discussion on the various PGPB activities and the potentiality of facultative halophilic/halotolerant PGPB in alleviating salt stress.
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