Bacterial inoculation positively affects the quality and quantity of flax under deficit irrigation regimes

AIM

The present research was conducted to investigate the effect of plant growth-promoting rhizobacteria (PGPR) and deficit irrigation on quality and quantity of flax under field and pot conditions to determine bacterial efficiency and to decrease water deficit effects.

METHODS AND RESULTS

Initially, in vitro experiments were performed to determine the growth-promoting characteristics of bacteria. Then in the field, the effects of bacterial inoculation (control, Azotobacter chroococcum, Azospirillum lipoferum, Bacillus amyloliquefaciens, Bacillus sp. strain1 and Pseudomonas putida) on flax traits were evaluated at different irrigation levels (100, 75 and 50% crop water requirement). Bacterial treatments in the pot experiment were selected based on the field experiment results. The irrigation regimes in the pot and field experiments were the same and bacterial treatments included single, doublet and triplet applications of the bacteria. All the bacterial strains could solubilize phosphate, produce ammonia (except for Bacillus sp. strain1), indole acetic acid and siderophore (except P. putida). Field results indicated that the bacteria significantly mitigated the effects of water deficit. Compared with control plants, bacterial treatments increased the oil, linolenic acid, protein and sulphur content; the number of shoots and capsules; and the harvest index in the flax plants. Pot experimental results revealed that the combined inoculations were more effective than single inoculum treatments.

CONCLUSIONS

Bacterial inoculation alleviates deficit irrigation effects in flax plants.

SIGNIFICANCE AND IMPACT OF THE STUDY

The effectiveness of applying A. chroococcum, B. amyloliquefaciens and Bacillus sp. strain1 was confirmed, especially as a combination to protect flax against water deficit and to improve its nutritional quality and growth.

Stress tolerance in flax plants inoculated with Bacillus and Azotobacter species under deficit irrigation

Drought stress affects not only crop growth but also its morpho-physiological and biochemical traits to reduce crop productivity. The study reported in this article was designed and implemented to determine the effects of deficit irrigation and bacterial inoculation on flax plants. For this purpose, seeds were inoculated with Bacillus amyloliquefaciens (B₁ ), Bacillus sp. Strain1 (B₂ ), and Azotobacter chroococcum (A) as plant growth promoting rhizobacteria (PGPR). The individual inoculated plants were then grown under field conditions in 2015, while individually and in combination in pots in 2016. The irrigation regimes in either experiments included 50, 75 and 100% crop water requirement. Bacterial cultures were observed to produce ammonia (except B₂ ), indole acetic acid and siderophores. Results showed that the PGPRs significantly mitigated the effects of water deficit. Compared with the control plants, the bacterially-inoculated plants had an enhanced relative water content, plant height, water-soluble carbohydrate and proline contents and antioxidant enzyme activities, but a decreased malondialdehyde content. B₁ exhibited greater effects on most of the traits investigated under the field conditions rather than those with moderate and severe drought stress, while application of the triple bacteria in pots had greater effects on relative water content, carbohydrate and proline contents as well as malondialdehyde. The significant differences in abiotic stress indicators in PGPR-treated plants suggest that these bacteria could be used as biofertilizers to assist plant growth and to reduce the adverse effects of deficit irrigation.

Subject: UV-B radiation and low temperature promoted hypericin biosynthesis in adventitious root culture of Hypericum perforatum

The hypericin is assumed as a highly demanded and key bioactive compound, which has antiviral, antimicrobial, antioxidant, and antitumor properties isolated from Hypericum perforatum. Nowadays, increasing bioactive molecules' contents through generating novel compounds is one of the major research objectives of H. perforatum biotechnology; however, this plant remains recalcitrant and unmanageable to Agrobacterium mediated transformation and genetic improvement programs. In order to overcome these challenges, many researchers have focused on this unruly herb using biotic and abiotic eliciting strategies. Therefore, two experiments were separately designed for the evaluation of two types of abiotic elicitors, aiming at increasing the productivity of hypericin in the adventitious root suspension culture of H. perforatum. The first one was accomplished to evaluate the effect of UV-B light elicitors (the exposure time of 30, 60, and 90 min) and the recovery treatment (with or without) on hypericin content while the second one was assessed the effect of various temperatures (4°C, 8°C, 16°C, and 25°C) in three different exposure times (24 h, 72 h, and 7 d). Based on the results, UV-B (60 min) treatment followed by the recovery produced 0.430 µg/g DW hypericin and was distinguished as the most effective UV-B elicitation treatment. In addition, a temperature of 4°C for a period of 72 hours is required to get the highest amount of hypericin content. These findings indicate the fact that hypericin biosynthesis is notably affected by UV-B exposure time and Low-temperature. The data also clearly elucidate further mechanisms of hypericin production in H. perforatum adventitious root culture.

Fast Quality Assessment of German Chamomile (Matricaria chamomilla L.) by Headspace Solid-Phase Microextraction: Influence of Flower Development Stage

For an adequate quality evaluation of aromatic plants grown under different conditions, a rapid, simple and sensitive method for the analysis of volatile constituents is indispensable. The main objective of the present study was to compare fast screening of German chamomile ( Matricaria chamomilla L.) by means of headspace solid-phase microextraction (HS-SPME) with conventional isolation of the essential oil (steam distillation-solvent extraction (SDSE)) for the differentiation of chamomile essential oil constituents. Flowers were harvested at two distinct development stages: stage I, when ligulate flowers start to develop and tubular flowers are still closed, and stage II, when tubular flowers are partially to completely opened.

Dried chamomile flowers at two development stages were extracted by means of both SDSE and HS-SPME, followed by GC-MS analysis. Among 30 compounds detected, ( E)-β-farnesene (49%), artemisia ketone (10%) and germacrene D (9%) were the predominant volatile components in the HS-SPME-extract, while α-bisabolol oxide A (42%), chamazulene (21%) and ( Z)-spiroether (8%) were the main essential oil constituents among the 13 compounds obtained by SDSE. After statistical analysis of the data, both techniques enabled the same conclusion: ( E)-β-farnesene was the only compound which showed significant differences between the two flower development stages.

These results suggest that HS-SPME-GC-MS can be used as a sensitive technique for the rapid screening and quality assessment of M. chamomilla.

Fast quality assessment of German chamomile (Matricaria chamomilla L.) by headspace solid-phase microextraction: influence of flower development stage

For an adequate quality evaluation of aromatic plants grown under different conditions, a rapid, simple and sensitive method for the analysis of volatile constituents is indispensable. The main objective of the present study was to compare fast screening of German chamomile (Matricaria chamomilla L.) by means of headspace solid-phase microextraction (HS-SPME) with conventional isolation of the essential oil (steam distillation-solvent extraction (SDSE)) for the differentiation of chamomile essential oil constituents. Flowers were harvested at two distinct development stages: stage I, when ligulate flowers start to develop and tubular flowers are still closed, and stage II, when tubular flowers are partially to completely opened. Dried chamomile flowers at two development stages were extracted by means of both SDSE and HS-SPME, followed by GC-MS analysis. Among 30 compounds detected, (E)-beta-farnesene (49%), artemisia ketone (10%) and germacrene D (9%) were the predominant volatile components in the HS-SPME-extract, while alpha-bisabolol oxide A (42%), chamazulene (21%) and (Z)-spiroether (8%) were the main essential oil constituents among the 13 compounds obtained by SDSE. After statistical analysis of the data, both techniques enabled the same conclusion: (E)-beta-farnesene was the only compound which showed significant differences between the two flower development stages. These results suggest that HS-SPME-GC-MS can be used as a sensitive technique for the rapid screening and quality assessment of M. chamomilla.