Effects of field inoculation with VAM and bacteria consortia on root growth and nutrients uptake in common wheat

This study investigated the effects of a commercial biofertilizer containing the mycorrhizal fungus Rhizophagus irregularis and the diazotrophic N-fixing bacterium Azotobacter vinelandii on root and shoot growth, yield, and nutrient uptake in common wheat (Triticum aestivum L.) in order to improve the sustainable cultivation of this widespread crop. The trials were carried out in controlled conditions (rhizoboxes) and in open fields over two years to investigate the interaction between inoculation and three doses of nitrogen fertilization (160, 120 and 80 kg ha1) in a silty-loam soil of the Po Plain (NE Italy). In rhizoboxes, efficient root colonization by R. irregularis was observed at 50 days after sowing with seed inoculation, together with improved root tip density and branching (+~30% vs. controls), while the effects of post-emergence inoculation by soil and foliar spraying were not observable at plant sampling. In the open, field spraying at end tillering significantly increased the volumetric root length density (RLD, +22% vs. controls) and root area density (+18%) after about two months (flowering stage) in both years under medium and high N fertilization doses, but not at the lowest N dose. In absence of inoculation, RLD progressively decreased with increased N doses. Inoculation had a negligible effect on grain yield and N uptake, which followed a typical N dose-response model, while straw Zn, P, and K concentrations were seldom improved. It is concluded that medium-high N fertilization doses are required to achieve the target yield and standards of quality (protein contents) in wheat cultivation, while the use of this mixed VAM-PGPR biofertilizer appears to be a sustainable mean for minimizing the adverse effects of chemical N fertilizers on root expansion and for improving the uptake of low-mobility nutrients, which has potentially relevant environmental benefits

Morphological changes and expressions of AOX1A, CYP81D8, and Putative PFP genes in a large set of commercial maize hybrids under extreme waterlogging.

Waterlogging is a severe abiotic stressor causing significant growth impairment and yield losses in many crops. Maize is highly sensitive to the excess of water, and against the background of climate change there is an urgent need for deeper insights into the mechanisms of crop adaptation to waterlogging. In the present study, changes in maize morphology at the 4\u20135 leaf stage and the expression of three candidate genes for flooding tolerance in plants subjected to six continuous days of waterlogging were recorded in 19 commercial hybrids and in the inbred line B73, with the aim of investigating the current variability in cultivated hybrids and identifying useful morphological and molecular markers for screening tolerant genotypes. Here it was demonstrated that root parameters (length, area, biomass) were more impaired by waterlogging than shoot parameters (shoot height and biomass). Culm height generally increased in stressed plants (by up to C24% vs. controls), while shoot biomass was significantly reduced in only two hybrids. Root biomass was reduced in all the hybrids, by an average of 30%, and significantly in 7 hybrids, while root length and area were even more severely reduced, by 30\u201355% vs. controls, depending on the hybrid. The earlier appearance of aerial roots seemed to be associated with greater root injuries. In leaves, the transcript of the PFP enzyme (phosphofructokinase), which is involved in glycolytic reactions, was markedly up-regulated (up to double the values) in half the waterlogged hybrids, but down-regulated in the others. The transcript of CYP81D8 (ROS-related proteins) in waterlogged plants exhibited relevant increases or strong decreases in level, depending on the hybrid. The transcript of the AOX1A gene, coding for a mitochondrial respiratory electron transport chain-related protein, was markedly down-regulated in all the treated hybrids. Expression analysis of these genes under extreme waterlogging only partially correlate with the shoot and root growth impairments observed, and AOX1A seems to be the most informative of them

Effects of Foliar-Applied Mixed Mineral Fertilizers and Organic Biostimulants on the Growth and Hybrid Seed Production of a Male-Sterile Inbred Maize Line

Plants of inbred maize lines are characterized by low vigor due to their high rates of homozygosity and may, therefore, benefit from additional nutrients and biostimulants supplied via foliar spraying. The present study innovatively investigated the effects of foliar treatment with three commercial organic-mineral fertilizers/biostimulants on a male-sterile inbred line of maize at the five-leaf stage. The three fertilizers were characterized by their following content: (i) NPK + hydrolyzed animal epithelium + micronutrients (named 'NPK + Hae + micro'), (ii) NK + humified peat (named 'NK + Hp'), and (iii) PK + Ascophyllum nodosum extracts (named 'PK + An'). The resulting shoot and root growth and seed yield and quality were compared to a control (C). Both NPK + Hae + micro and PK + An treatments enhanced root growth in the top 20 cm soil layer at the ten-leaf stage: root dry biomass increased by 80 and 24%, respectively, and the volumetric root length density by 61 and 17%. The two treatments also allowed for a larger number of commercial seeds to be produced (on average +16 bags per gross hectare vs. C) owing to a better seed caliber, which consequently reduced rates of seed disposal (-11 and -20% for PK + An and NPK + Hae + micro, respectively) and, in the case of NPK + Hae + micro, due to an increment in the number of kernels per ear (+5% vs. C). These effects were not associated with any significant changes in shoot growth, height, or leaf net CO2 assimilation. In this preliminary trial, peak commercial benefit was obtained with the use of hydrolyzed epithelium together with macro- and micronutrients. Further investigation into application timing and dose, and the means by which these products alleviate the effects of low vigor and stress conditions observed particularly under mechanical emasculation is, however, necessary for their full exploitation in the production of hybrid maize seeds

Effects of seed-applied biofertilizers on rhizosphere biodiversity and growth of common wheat (Triticum aestivum L.) in the field

In order to reduce chemical fertilization and improve the sustainability of common wheat (Triticum aestivum L.) cultivation, maintaining at the same time high production and quality standards, this study investigated the effects of three commercial biofertilizers on rhizosphere bacterial biomass, biodiversity and enzymatic activity, and on plant growth and grain yield in a field trial. The wheat seeds were inoculated with the following aiding microrganisms: (i) a bacterial consortium (Azospirillum spp. + Azoarcus spp. + Azorhizobium spp.); and two mycorrhizal fungal-bacterial consortia, viz. (ii) Rhizophagus irregularis + Azotobacter vinelandii, and (iii) R. irregularis + Bacillus megaterium + Frateuria aurantia, and comparisons were made with noninoculated controls. We demonstrate that all the biofertilizers significantly enhanced plant growth and nitrogen accumulation during stem elongation and heading, but this was translated into only small grain yield gains (+1%\u20134% vs controls). The total gluten content of the flour was not affected, but in general biofertilization significantly upregulated two high-quality protein subunits, i.e., the 81 kDa high-molecular-weight glutenin subunit and the 43.6 kDa low-molecular-weight glutenin subunit. These effects were associated with increases in the rhizosphere microbial biomass and the activity of enzymes such as b-glucosidase, a-mannosidase, bmannosidase, and xylosidase, which are involved in organic matter decomposition, particularly when Rhizophagus irregularis was included as inoculant. No changes in microbial biodiversity were observed. Our results suggest that seed-applied biofertilizers may be effectively exploited in sustainable wheat cultivation without alteringthe biodiversity of the resident microbiome, but attention should be paid to the composition of the microbial consortia in order to maximize their benefits in crop cultivation

Screening of crop varieties for agroforestry farming: the case of durum wheat in organic olive orchards in southern France

In this study, it was investigated a durum wheat/olive tree agroforestry model in the Mediterranean climate conditions of Southern France under organic farming system. It was studied two agroforestry treatments where the olive tree canopies intercepted the 33 % of PAR in one case and the 55% of PAR in the other case, due to different canopy size. The two agroforestry treatments were compared with a durum wheat control system, grown in full sun conditions. The following five topics were investigated: 1 - impact of agroforestry on the microclimate and the edaphic environment experienced by crops; 2 - impact of agroforestry on durum wheat phenology; 3 - impact of agroforestry on durum wheat yield, yield components and morphology; 4 - screening durum wheat varieties for agroforestry: searching for an appropriate test; 5 - impact of associated field crops on organic olive orchards production

Approcci agronomici ed ecosistemici innovativi per migliorare la resilienza e la qualità del frumento in risposta agli stress abiotici

L'obiettivo di questo progetto è stato quello di migliorare la resilienza e la qualità del frumento tenero, utilizzando sia un approccio agronomico che ecosistemico. Le due strategie innovative studiate sono (i) l’applicazione fogliare di citochinine dopo la fase di fioritura e (ii) l'implementazione di sistemi agroforestali. Per quanto riguarda l'approccio agronomico, lo studio bibliografico sugli effetti dell'applicazione di fitormoni nei cereali ha rivelato la possibile efficacia di questa tecnica per aumentare la tolleranza agli stress abiotici. Non sono invece disponibili indicazioni sull’epoca di applicazione in studi di pieno campo. Pertanto, è stata condotto una sperimentazione confrontando quattro epoche di applicazione di CKs a partire dalla fioritura. È stato dimostrato che, nel caso di elevate temperature e stress idrico a fine ciclo, l'applicazione di CKs va programmata in fioritura per ottenere un significativo prolungamento dell'attività fotosintetica fogliare. Il contenuto proteico è aumentato fino a +1,2% (incremento assoluto) rispetto a C, e la resa del 4%. È stata condotta una sperimentazione biennale per corroborare questi risultati in relazione alle diverse condizioni climatiche. Si è potuto concludere che in presenza di basse temperature e precipitazioni abbondanti a fine, l’epoca di applicazione più efficiente per la distribuzione di CKs è in pos-fioritura (10 giorni dopo). In questo caso, il contenuto di clorofilla fogliare è stato mantenuto elevato fino a inizio giugno, e sia la resa che la qualità hanno visto variazioni positive. Indipendentemente dall'anno di studio, la qualità tecnologica e il valore nutritivo delle cariossidi di frumento sono stati positivamente influenzati dall’applicazione di CKs, con un maggior rapporto glutenine/gliadine (fino a +14% nel 2018), senza osservare variazioni del contenuto totale di glutine. Per quanto riguarda l'approccio ecosistemico, è stata svolta una approfondita indagine bibliografica per valutare l’effetto degli alberi sulla resilienza delle colture nei sistemi agroforestali (AF). Il frumento e l'orzo hanno subito gli impatti sulla resa più limitati, rispetto a colture come il mais. Per simulare l'effetto degli alberi, è stata implementata una sperimentazione di ombreggiamento artificiale con diversi livelli di riduzione della radiazione fotosinteticamente attiva (-30% e -50% PAR) al fine di osservare gli effetti su varietà di frumento moderne e vecchie. L'ombreggiamento moderato (-30% PAR) ha ritardato favorevolmente la senescenza fogliare e aumentato il contenuto proteico di +1,8%, con miglioramenti della resa (+8%) nella varietà moderna Bologna. Le vecchie varietà, di taglia elevata, sono state danneggiate dalle abbondanti precipitazioni e allettamento in primavera, e hanno mostrato significative perdite di resa (fino a -67%). Tuttavia, questi risultati dovranno essere confermati in reali sistemi AF, dove il riparo degli alberi potrebbe ridurre l'impatto di condizioni climatiche avverse. Infatti, all'interno di un sistema alley-cropping con filari di pioppo distanziati 40 m, sono state osservate variazioni positive sia della resa che della qualità della granella nella zona di interazione con gli alberi. Sono state nuovamente osservate risposte contrastanti in funzione della varietà, in quanto una varietà biscottiera ha presentato un aumento di resa maggiore rispetto ad una varietà panificabile in prossimità di alberi. Sono stati identificati alcuni key traits dell’adattabilità all'AF, come il rapporto tra l'indice di area fogliare e di area dei culmi, e la persistenza dell'attività fotosintetica fogliare durante il riempimento della granella, che contribuiscono ad una migliore intercettazione della radiazione.Heat stress and drought during the late stages of the wheat cycle promote the acceleration of crop phenology through the anticipation of leaf senescence, leading to grain yield and quality impairments. The objective of this PhD project was to enhance resilience and quality of common wheat, by investigating both an agronomic and an ecosystem approach. The two innovative strategies proposed here are (i) foliar spraying of cytokinins after wheat flowering, and (ii) implementation of agroforestry systems. As regards to the agronomic approach, a systematic review work on the effects of the exogenous application of phytohormones in cereals revealed the promising potential of this technique to enhance tolerance to various abiotic stress. Summarizing the available knowledge allowed to highlight the effectiveness of cytokinins (CKs) exogenous supply in delaying leaf senescence and promoting stress tolerance. However, indications on the time of application in open field are still lacking. Therefore, it was conducted a field study with the aim at investigating four times of CKs application starting from flowering, and three doses, using a commercial product containing 6-benzyladenine (6-BA). Here it was demonstrated that, under high temperatures and drought (like in 2018 season), CKs application should be scheduled at flowering to achieve a significant prolonging of leaf photosynthetic activity during grain filling. With 100 ppm of 6-BA, grain protein content was improved by up to 1.2%, as absolute increment vs. C, and yield by 4%. A two-year field trial was carried out to corroborate these findings in relation to different climatic conditions. When low temperatures and abundant rainfall occur during grain filling (like in 2019 season), the most efficient timing of CKs spraying was after flowering (10 days). In this case, leaf chlorophyll content was maintained high until early-June, and both grain yield and protein content were improved, although not significantly. Regardless the year of study, the technological quality and nutritional value of wheat grains were positively impacted by CKs, as showed by the higher glutenins/gliadins ratio (+14% in 2018 and +7% in 2019), with no changes in the total gluten content, and higher minerals concentration (+10% of P, Ca, Mg and K). As regards the ecosystem approach, a synthesis work was carried out to disentangle the potential of tree rows to improve resilience of grain crops within temperate agroforestry (AF) systems. Common wheat revealed the least negative impacts on crop yield when placed close to trees, as compared to light-demanding crops such as maize. To mimic the effect of trees, artificial shading was implemented with different levels of photosynthetic active radiation reduction (-30% and -50% PAR) in order to investigate the effects on modern and old wheat varieties. Moderate shading (-30% PAR) positively delayed leaf senescence and increased grain protein content by +1.8% vs. C, together with slight improvements of grain yield (+8%) in the modern var. Bologna. The old high-size varieties were damage by abundant rainfall and lodging in spring, and showed significant yield losses (up to -67%). However, these finding should be corroborated in real AF, where the shelter of trees might reduce the impact of adverse climatic conditions. Indeed, within a poplar alley-cropping system with 40 m apart tree rows, it was observed positive variations in both grain yield and quality of wheat in the interaction zone with trees. Contrasting responses, depending on variety choice, were again observed, as a “biscuit-making” wheat variety showed higher yield gain than a “bread making” variety (+14% and +4% respectively, vs. C) in the proximity of trees. Some key traits of adaptability to AF were revealed, such as the ratio between leaf and culm area indexes, and the lengthening of flag leaf photosynthetic activity during grain filling, thereby contributing to better light harvesting