Browsing by Person "Mamun, Abdullah Al"

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Bio-effector based fertilization strategies to improve drought stress tolerance and phosphate efficiency in potato
(2024) Mamun, Abdullah Al; Neumann, Günter
Due to shallow root systems, potato is considered as a drought sensitive crop. To counteract these limitations, application of plant growth-promoting microorganisms (PGPMs) is discussed as a strategy to improve nutrient acquisition and biotic and abiotic stress resilience. However, particularly initial root colonization by PGPMs can be affected by stress factors with negative impact on root growth and activity or the survival of PGPMs in the rhizosphere. Initial screening experiments (Chapter 3) investigated drought-protective effects of six fungal and bacterial inoculants and ten combinations thereof (microbial consortia) on vegetative growth, nutritional status and tuberization of potato under controlled conditions. It was hypothesized that microbial consortia would offer improved drought protection as compared with single strains due to complementary or synergistic effects, with a differential impact also of the N fertilization management. Under nitrate fertilization, a 70% reduction in water supply over six weeks reduced shoot and tuber biomass by 30% and 50%, respectively and induced phosphate (P) limitation. The P-nutritional status was significantly increased above the deficiency threshold by three single strain inoculants and eight consortia. This was associated with the presence of the arbuscular mycorrhizal (AM) inoculant Rhizophagus irregularis MUCL41833 (5 cases) and stimulation of root growth (5 cases). Additionally, Bacillus amyloliquefaciens FZB42 and an AM + Pseudomonas brassicacearum 3Re2-7 combination significantly reduced irreversible drought-induced leaf damage after recovery to well-watered conditions. However, despite beneficial effects on vegetative growth, the microbial inoculants did not mitigate drought-induced limitations in tuber formation, neither in greenhouse culture nor in field experiments. Contrary to nitrate supply, ammonium dominated fertilization significantly increased tuber biomass under drought stress, which was further increased by additional AM inoculation. This was associated with (i) improved enzymatic detoxification of drought-induced reactive oxygen species (ROS), (ii) improved osmotic adjustment in the shoot tissue (glycine betaine accumulation), (iii) increased shoot concentrations of ABA, jasmonic acid and indole acetic acid (IAA), known to be involved in drought stress signaling and tuberization, and finally (iv) reduced irreversible drought-induced leaf damage. Additional application of the bacterial inoculants FZB42, 3Re2-7 or Herbaspirillum further improved ROS detoxification by increased production of antioxidants. However, this resulted in stimulation of biomass allocation towards shoot growth at the expense of tuber development. The results demonstrated that compared with single strain inoculants, microbial consortia used as inoculants can increase the probability for complementary plant-protective effects under environmental stress conditions. However, the absolute effect size is not always different. Drought-protective effects on vegetative growth do not necessarily translate into yield benefits and are affected by the form of N supply and the selected inoculant strains. Application of silicatic soil conditioners to improve soil water relationships under drought stress may be strategy to support rhizosphere establishment of PGPM inoculants with drought-protective potential under conditions of water deficit. In Chapter 4, perspectives for the use of commercial silicatic soil conditioners (SC) supposed to improve soil water retention, were investigated. The SC products were based on combinations of silicatic rock powder with lignocellulose polysaccharides (Sanoplant® = SP) or polyacrylate (Geohumus® = GH). It was hypothesized that SC applications would support beneficial plant-inoculant interactions with Rhizophagus irregularis MUCL41833 & Pseudomonas brassicacearum 3Re2-7 on a silty loam soil-sand mixture under water deficit conditions. Although no significant SC effects on WHC and total plant biomass were detectable, the SC-inoculant combinations increased the proportion of leaf biomass not affected by drought stress symptoms (chlorosis, necrosis) by 66% (SP) and 91% (GH). Accordingly, osmotic adjustment (proline, glycine betaine accumulation) and ROS detoxification (ascorbate peroxidase, total antioxidants) were increased. This was associated with elevated levels of phytohormones involved in stress adaptations (abscisic-, jasmonic-, salicylic-acids, IAA) and reduced ROS (H2O2) accumulation in the leaf tissue. In contrast to GH, the SP treatments additionally stimulated AM root colonization. Finally, the SP-inoculant combination significantly increased tuber biomass (82%) under well-watered conditions and a similar trend was observed under drought stress, reaching 81% of the well-watered control. The P status was sufficient for all treatments and no treatment differences were observed for stress-protective nutrients, such as Zn, Mn, or Si. By contrast, GH treatments had negative effects on tuber biomass, associated with excess accumulation of Mn and Fe in the leaf tissue close to the toxicity levels. The findings suggest that inoculation with the PGPMs in combination with SC products (SP) can promote physiological stress adaptations and AM colonization to improve tuber yield of potato, independent of effects on soil water retention. However, this does not apply for SC products in general. Chapter 5 investigated an optimized PGPM application technology based on granulated organic fertilizer formulations (Minigran®), specifically adapted to improve the shelf life of selected microbial consortia. Microbial consortia were based on selected strains of Pseudomonas brassicacearum (Cons1), Paraburkholderia phytofirmans (Cons2) and Paraburkholderia phytofirmans+ Trichoderma asperelloides (Cons3) in combinations with arbuscular mycorrhizal fungi (Rhizophagus irregularis), applied in the protective organic Minigran® formulations with or without additional application of the silicatic lignocellulose soil conditioner (Sanoplant®). At the end of a two-weeks recovery period from six weeks drought stress at a soil moisture level of 25% soil water holding capacity, all tested Minigran-Consortia formulations reduced the proportion of irreversibly drought-damaged leaves by 35-88%, irrespective of the soil conditioner treatments. Already the Minigran blank formulations had a certain beneficial effect on enzymatic (ascorbate peroxidase) and particularly non-enzymatic (total antioxidants) detoxification of reactive oxygen species (ROS), indicated by a significantly reduced ROS (H2O2) accumulation in the leaf tissue. This effect was further improved by introduction of the microbial consortia. Both, the Mingran blank formulations and the Minigran-consortia combinations, affected the hormonal status in the leaf tissue towards increased ABA/Gibberellic acid (GA) ratios and increased IAA levels, known to support tuber initiation and tuber growth and increased the jasmonic acid concentrations involved in abiotic stress signalling. The Minigran blank formulations also increased the root colonisation with AM fungi, which was further increased by introduction with the consortia, particularly in combination with the soil conditioner. Beneficial effects of the consortia on tuber biomass were mainly recorded in combination with the soil conditioner and even reached the values of well-watered controls with NPK fertilisation in case of Cons1. This was associated with a compensation of drought-induced reductions in P and K accumulation in the shoot tissue. Tuber quality was improved by increased starch concentrations with a simultaneous reduction of soluble sugars. The findings suggest that application of selected organic microbial consortia formulations in combination with silicatic soil conditioner has potential to improve the drought tolerance of potato and requires further investigation under field conditions.
Microbial consortia versus single-strain inoculants as drought stress protectants in potato affected by the form of N supply
(2024) Mamun, Abdullah Al; Neumann, Günter; Moradtalab, Narges; Ahmed, Aneesh; Dupuis, Brice; Darbon, Geoffrey; Nawaz, Fahim; Declerck, Stephane; Mai, Karin; Vogt, Wolfgang; Ludewig, Uwe; Weinmann, Markus
This study investigated the drought protection effects of six fungal and bacterial inoculants and ten consortia thereof on vegetative growth, nutritional status, and tuberization of potato under controlled and field conditions. It was hypothesized that microbial consortia offer improved drought protection as compared with single strains, due to complementary or synergistic effects, with differential impacts also of N fertilization management. Under NO3− fertilization, a 70% reduction in water supply over six weeks reduced shoot and tuber biomass of non-inoculated plants by 30% and 50%, respectively, and induced phosphate (P) limitation compared to the well-watered control. The P nutritional status was significantly increased above the deficiency threshold by three single-strain inoculants and eight consortia. This was associated with the presence of the arbuscular mycorrhizal fungus (AMF) inoculant Rhizophagus irregularis MUCL41833 (five cases) and stimulation of root growth (five cases). Additionally, Bacillus amyloliquefaciens FZB42 and AMF + Pseudomonas brassicacearum 3Re2-7 significantly reduced irreversible drought-induced leaf damage after recovery to well-watered conditions. However, the microbial inoculants did not mitigate drought-induced reductions in tuber biomass, neither in greenhouse nor in field experiments. By contrast, NH4+-dominated fertilization significantly increased tuber biomass under drought stress (534%), which was further increased by additional AMF inoculation (951%). This coincided with (i) improved enzymatic detoxification of drought-induced reactive oxygen species (ROS), (ii) improved osmotic adjustment in the shoot tissue (glycine betaine accumulation), (iii) increased shoot concentrations of ABA, jasmonic acid, and indole acetic acid, involved in drought stress signaling and tuberization, and (iv) reduced irreversible drought-induced leaf damage. Additional application of bacterial inoculants further improved ROS detoxification by increasing the production of antioxidants but stimulated biomass allocation towards shoot growth at the expense of tuber development. The results demonstrated that microbial consortia could increase the probability of drought protection effects influenced by the form of N supply. However, protective effects on vegetative growth do not necessarily translate into yield benefits, which can be achieved by adequate combination of inoculants and fertilizers.